Despite numerous investigations, the impact of tizanidine, an anti-spastic medication, on changes in reflex and muscle mechanical properties in spasticity remains unclear. This study was designed to help us understand the mechanisms of action of tizanidine on spasticity in spinal cord injured subjects with incomplete injury, by quantifying the effects of a single dose of tizanidine on ankle muscle intrinsic and reflex components.A series of perturbations was applied to the spastic ankle joint of twenty-one spinal cord injured subjects, and the resulting torques were recorded. A parallel-cascade system identification method was used to separate intrinsic and reflex torques, and to identify the contribution of these components to dynamic ankle stiffness at different ankle positions, while subjects remained relaxed.Following administration of a single oral dose of Tizanidine, stretch evoked joint torque at the ankle decreased significantly (p < 0.001) The peak-torque was reduced between 15% and 60% among the spinal cord injured subjects, and the average reduction was 25%. Using systems identification techniques, we found that this reduced torque could be attributed largely to a reduced reflex response, without measurable change in the muscle contribution. Reflex stiffness decreased significantly across a range of joint angles (p < 0.001) after using tizanidine. In contrast, there were no significant changes in intrinsic muscle stiffness after the administration of tizanidine.Our findings demonstrate that tizanidine acts to reduce reflex mechanical responses substantially, without inducing comparable changes in intrinsic muscle properties in individuals with spinal cord injury. Thus, the pre-post difference in joint mechanical properties can be attributed to reflex changes alone. From a practical standpoint, use of a single "test" dose of Tizanidine may help clinicians decide whether the drug can helpful in controlling symptoms in particular subjects. Spasticity can disrupt activities of daily life ,2, and h2 noradrenergic (NE) agonist, which is incompletely studied, but is thought to act to depress dorsal horn interneuron excitability [2 NE agonists ["Hypertonia" is one of the primary clinical features associated with spinal cord injury ,3. Hypertability . It has tability ,15-17 antability ,15,17,18tability ,12,13, mtability -12, and tability . Furtheragonists .2-adrenergic agonist and presumably acts on presynaptic terminals and on interneurons [Tizanidine is an αrneurons ,22 withirneurons ,23. ThusA number of studies have examined the therapeutic effects of tizanidine ,13,15,24More importantly, although hypertonia arises broadly from changes in the mechanical properties of passive tissues, muscles, and from abnormal reflexes -31, thesIn earlier publications, we described a system identification method to characterize joint dynamic stiffness and to separate it muscular (intrinsic) and reflex contributions to overall stiffness analytically ,32. We sForty individuals with incomplete spinal cord injured (37.6 ± 13.2 years) participated in this study. All subjects had chronic spinal cord injury of between 2 and 18 years (8.5 ± 4.7 years) duration, with different degrees of spasticity. Twenty subjects received tizanidine and repeated joint perturbations including tests before and after tizanidine administration. Twenty served as controls, receiving no tizanidine and a more limited set of joint perturbations. Two subjects in the tizanidine group were unable to complete data collection because of their time constraints, and their data are not included here.Patients had sustained a traumatic, motor incomplete non-progressive spinal cord injury, with an American Spinal Injury Association (ASIA) impairment scale classification of C or D indicating motor incomplete lesions. In addition, the neurological level of injury was above T10, spasticity was present in the leg, and the study was initiated a minimum of 1 year post-injury.Subjects gave informed consent to the experimental procedures, which had been approved by Northwestern University Institutional Review Board.All spinal cord injured subjects were evaluated clinically using the modified 6-point Ashworth scale to assess the severity of spasticity ,34.  and defined as zero.Electromyograms (EMGs) were recorded from tibialis anterior and lateral gastrocnemius for the ankle joint using bipolar surface electrodes . Position, torque, and EMGs were filtered at 230 Hz to prevent aliasing, and sampled at 1 kHz by a 16 bit A/D.We provided a single dose of 2 mg, a relatively small dose. This dose level usually shows effects, but does not cause major side effects. Thus, this can be tolerated by vast majority of patients. Subjects were tested before and after the administration of tizanidine. Tizanidine effects begin within 30 minutes, and last for up to 4 hours, so we began recording 60 minutes after drug administration..Isometric maximum voluntary conractions were determined by having subjects contract the ankle muscles maximally toward plantarflexion and dorsiflexion directions at neutral position (90°); torque and EMG were sampled for 5 sec. Measurements were repeated at least twice and the best measure was considered as maximum voluntary contraction.Range of motion was determined with the subject's ankle attached to the motor. The ankle range of motion was recorded using the goniometer built onto the motor, but under passive conditions, to guarantee safety Mean amplitude was estimated by slowly moving the joint until the examiner perceived rapidly increasing resistance or the subject reported discomfort. Measurements were done 3 times.To evaluate the peak-torque responses after tizanidine, a series of 5 large, rapid stretch and hold dorsiflexion perturbations was applied to the ankle joint with displacement amplitude of 30°, stretch velocity of 200 deg/s, and hold time of approximately 2.4 s. This movement velocity is routinely sufficient to elicit stretch reflex responses. Stretch trials were applied with the joint in 20° plantarflexion and the torque and EMG responses were ensemble-averaged.To identify overall stiffness properties and to separate the reflex and intrinsic components, we used pseudorandom binary sequence inputs with amplitude of 2° and a switching interval of 150 ms. These perturbations were applied to the ankle of drug recipients and to controls for a period of 30 s at each joint position. Trials were conducted at multiple different joint positions from full plantar flexion to maximum tolerable dorsiflexion at 5° intervals.These perturbations are appropriate to characterize the joint dynamic stiffness and to separate its neural and muscular components  and theyPulse trials were applied before and after pseudorandom binary sequence trials to control for changes in the subject's state, as quantified by the overall level of excitability of motoneurons. Five small pulses with an amplitude of 2° and pulse-width of 40 ms were applied to the ankle; EMGs from tibialis anterior and gastrocnemius and ankle torque were recorded and ensemble-averaged. The amplitudes of the reflex responses were used as an empirical measure of stretch reflex excitability. Changes in response amplitudes greater than 10% were taken as evidence of a change in the subject's state, due to fatigue or other factors, and data for the trial were discarded. This occurred very rarely; in most experiments no trials were discarded.We used a parallel cascade system identification technique to separate reflex and intrinsic contributions to ankle dynamic stiffness. This technique, described in detail in earlier publications ,35.The intrinsic stiffness was estimated in terms of a linear Impulse Response Function (IRF), which is a curve relating position and torque. The IRF characterizes the behavior of the system over its entire range of frequencies. The intrinsic IRF was convolved with the experimental input to predict the intrinsic torque.The reflex pathway was modeled as a differentiator in series with a delay, a half-wave rectifier (indicating the direction of stretch), and a dynamic linear element. Reflex stiffness was estimated by determining the IRF between half-waved rectified velocity as the input and reflex torque (the difference between the net joint torque and the predicted intrinsic torque) as the output. The reflex IRF was convolved with the half-waved velocity, as input, to predict the reflex torque.IRFs were assessed in terms of the percentage of the output (torque) variance accounted for.Intrinsic and reflex stiffness gains were calculated by fitting linear models to their IRF curves .We used two-way ANOVA analyses to test for significant main effects due to tizanidine, joint positions, or their interactions. The results can tell us if there were significant differences due to main effects and/or their interactions. Tukey post-hoc comparisons were performed to find at which positions the differences between pre- and post-tizanidine were significant.Standard t-tests procedures were used to test for significant changes in peak torque and maximum voluntary contractions due to tizanidine.Figure Figure In contrast to the peak torque, there was no significant difference in maximum voluntary contractions between Pre and Post tizanidine administration.The torque response has two distinct components Figure ; a compoGR, panel A) and intrinsic stiffness gain  of the spastic ankle post- versus pre-tizanidine for all spinal cord injured subjects, and for all positions. GR for all subjects were well located below the diagonal line, indicating that GR was significantly lower Post as compared with Pre drug administration (p < 0.001). In contrast, the points for the K were mostly clustered around the unity line, and did not show significant differences between post- and pre-tizanidine. These results demonstrate that the significant decrease observed in peak-torque responses after tizanidine  and K (panel B) as a function of ankle position for both Pre and Post treatment groups. There was a significant effect due to position on both the Pre and Post groups (p < 0.001). The differences increased when ankle was stretched toward dorsiflexion, reached its maximum at the first 5° dorsiflexion, and declined sharply with further dorsiflexion. Tukey post-hoc analysis confirmed that (GR) was significantly lower in Post vs Pre treatment group, from mid-plantarflexion (20° plantarflexion) to full-dorsiflexion (20° dorsiflexion) (p < 0.001).Figure The group position-dependent behavior was consistent but the inter-subject variability was high from mid-plantarflexion to full-dorsiflexion as demonstrated by the large standard error bars associated with the means.GR, there was no significant difference in K between Pre and Post treatment groups  as changes were more than 30% in most subjects (more than 75% of subjects), indicating consistent impact of the single dose on reflex mechanical responses. The small standard deviation error bars show that the changes were independent of position.Figure GR and K values between this final and initial measure. This indicates that the changes observed following tizanidine were attributable solely to the actions of the drug, and not to time or history dependent changes in reflex response.We did not find a significant change in control subjects' state over the course of each experiment, as evidenced by the absence of changes exceeding 10% in reflex torque. Because of this, we limited the pseudorandom binary sequence trials only at the neutral position in the control group. We found no significant changes in The focus of this study was to quantify the effects of single dose of tizanidine on the neuromuscular abnormalities associated with spasticity, with particular emphasis on the relative contributions of changes in reflexes versus changes in intrinsic neuromuscular properties.Prior studies on tizanidine have focused mostly on clinical measurements of spasticity or weakness. Many of these studies, have investigated the effects of tizanidine on spasticity using the Ashworth scale and the pendulum test ,24. Othe2 adrenergic agonist on stretch reflexes in spastic subjects are substantial, and that they take effect quickly, and at a relatively small dose. A single 2 mg dose of tizanidine was routinely effective, reducing joint torque substantially within 60 minutes, by a magnitude of 15% to 60%.Our study findings are that the actions of tizanidine, an αSecond, though perhaps to be anticipated, the study affirms that the effects of the agent on limb spasticity are mediated by reflex changes, rather than by direct changes in muscle contractility. Although this is the accepted view of tizanidine actions, there have been reports of loss of voluntary muscle strength ,10,12, wIt is likely that the actions of the agent are mediated, at least in part, at interneuronal sites ,22, and Finally, the findings of our systems identification methods affirm that changes in joint torque following a single dose of tizanidine are attributable almost entirely to changes in stretch reflex contributions, without changes in the intrinsic muscle contribution to net joint torque. Although these (reflex) changes conform with the known physiology/pharmacology of tizanidine ,23, it mThe authors declare that they have no competing interests.MMM designed the study, supervised data collection and analysis, and participated in interpreting and writing the manuscript. DC referred the patients and participated in interpreting data, and WZR participated in interpreting data and writing the manuscript. All authors read and approved the final manuscript.


A 66-year old female with HIV-negative classic Kaposi's sarcoma responded to mTOR targeting by rapamycin. The response was well documented by PET-CT. This case provides supporting evidence that the mTOR pathway may be important in the tumorigenesis of KS and that rapamycin may have activity in this disease. Kaposi's sarcoma (KS) is an indolent vascularized tumor that has been subdivided into several variants including classicKS, African endemic KS, iatrogenic (post transplantation) KS, and epidemic, acquired immunodeficiency syndrome-associated (AIDS-associated)KS. It behaves more aggressively in HIV-related or in post transplant patients,but its classic form may be more indolent althoughdisfiguring does not commonly result in early mortality. Clinically,KS forms dark blue or purplish macular lesions or spindle-shaped nodularlesions that occur in the skin, lymphoid, respiratory, and gastrointestinaltissues. Histological picture shows networks of spindle-shaped cells andvascular spaces surrounded by an endothelial cell layer. Therapy for localizeddisease is surgery or radiation therapy, while widespread disease may betreated by systemic chemotherapy . A novelA 66-year old otherwise healthyCaucasian female patient presented with metastatic HIV-negative Kaposi'ssarcoma (KS), diffusely involving the skin and soft tissues of the plantar surface, legs,and thighs. During a prolonged interval of palliative radiation therapy and variousineffective systemic chemotherapeutic regimens that included vinblastine,etoposide, doxorubicin, and alpha-interferon. The disease progressed and spreadto the bowel and to the soft tissues of the left arm and to the inguinal,mediastinal, axillary, and cervical nodes. Clinically, the patient had aKarnofsky's performance status of 80–70%, andcomplained of weakness, and pain in her lower limbs. Radiologically, the disease was welldocumented by PET-CT performed on October 18, 2006 . After oOur case points to two important observations. First is the role of mTORas a therapeutic target in HIV-negative classic KS. We observed thatrapamycin monotherapy was more active and better tolerated than systemic,conventional chemotherapy in this patient. The second is monitoring of theobjective response by PET-CT imaging. The clinical improvement correlated withmetabolic shutdown of glucose metabolism in the sarcoma nodules, as documentedby decrease in FDG uptake. PET-CT as atool for staging and monitoring of therapy has been suggested for vasculartumors .3. This in turn leads to activation of Aktfollowed by activation of mTOR. MTOR then phosphorylates and activates p70S6k,the kinase which phosphorylates the ribosomal protein S6 thereby promoting therecruitment of the 40S subunit into actively translating polysomes [Rapidly accumulating dataimplicate rapamycin, a natural product produced by Streptomyces hygroscopicusas a potential anticancer agent. While originally identified 20 years agoduring antibiotic screening and found to display remarkable antifungalactivity, rapamycin was subsequently recognized to possess highly potentimmunosuppressive properties  and has olysomes , 9. Therolysomes , 11.Rapamycin binds to itsintracellular receptor protein FKBP12 . NotablyThe antiproliferative activity ofrapamycin was first evaluated in variety of murine tumor cell lines and tumormodel systems. In those experiments, rapamycin was found to exhibit impressiveantitumor activity inhibiting the growth of lymphoma cell lines, small celllung cancer cell lines, rhabdomyosarcoma cell lines, pancreatic cancer celllines and more (reviewed in ). MoreovThe role of mTOR signaling pathway in pathogenesis of Kaposi's sarcomahas been elucidated . A humanThediscovery that the development of KS may be dependent on vGPCR dysregulationsuggests that the development of new mechanism-based therapeutic modalitiesspecifically targeting this viral protein (or its downstream targets) may proveto be an effective treatment strategy . SeveralInconclusion, this case provides supporting evidence that the mTOR pathway may beimportant in the tumorigenesis of KS and that rapamycin may have activity inthis disease. A phase II study for assessing the exact role of mTOR inhibitors inthis disease is warranted.


In this Surgery , was not Surgery , in ordeBeyond a doubt, a detailed description of the molecular neuropathology of TBI represents a challenging task, which is difficult to describe in just a few paragraphs. However, the authors could have expanded their article to include some of what we consider "key" pathways in the cellular and molecular pathophysiology of TBI Figure . For exa"missing link" between molecular mechanisms and therapeutic concepts in TBI. Unfortunately, the review article fails to provide a bridge between the two entities. In addition, many of the current therapeutic approaches and promising new strategies in search of the pharmacological "golden bullet" are missing [Finally, as a minor comment, the authors should pay more attention to accuracy in the citation of the pertinent literature. For example, reference #10 is claimed to support a statement on interleukins and cerebral edema, when in fact the citation refers to a publication on programmed cell death in nematodes. Several other examples of inadequate reference to the literature could be mentioned. Finally, the title chosen by the authors appears problematic. The authors claim to provide the  missing . While aet al. [In summary, we realize that providing an encompassing and scientifically accurate review on the topic represents a virtually impossible task. We are therefore grateful for the review by Veenith et al.  and we hThe authors declare that they have no competing interests.MAF and PFS wrote the manuscript. WRS and SJM critically revised the paper. All authors approved the final version of this manuscript.


Ductal stenting is an attractive alternative to conventional shunt surgery in duct dependent congenital heart disease as it avoids thoracotomy and its related problems. With today's generation of coronary stents which have better profile, flexibility and trackability, ductal stenting may be achieved safely and with considerably less difficulty than previously described.As in Blalock-Taussig (BT) shunt, ductal stenting is indicated mainly in duct-dependent cyanotic lesions chiefly in the neonatal period. Unlike the Patent ductus arteriosus (PDA) as an isolated lesion, the ductus in cyanotic heart disease has a remarkable morphologic variability. The ductus tends to arise more proximally under the aortic arch, giving rise to a vertical ductus or occasionally it may arise from the subclavian artery. It also tends to be long and sometimes very tortuous, rendering stent implantation technically impossible. The ductus in these patients may also insert onto one of the branch pulmonary arteries with some stenosis at the site of insertion. The ductus in Tetralogy of Fallot with pulmonary atresia (TOF-PA) tend to exhibit these morphologic features and to a lesser degree in transposition of great arteries with ventricular septal defect and pulmonary atresia (TGA-VSD-PA) and the more complex forms of univentricular hearts. In the preliminary angiographic evaluation, it is important to delineate these morphologic features as the basis for case selection.Ductal stenting may be done by the retrograde femoral artery route or the antegrade transvenous route depending on the ductus morphology and the underlying cardiac lesion. The detailed techniques and essential hardware are described. Finally, major potential complications of the procedure are described. Acute stent thrombosis is the most serious and potentially catastrophic. Emergent treatment with thrombolytic therapy and mechanical disruption of thrombus are required. With proper case selection, appropriate technique and the right hardware ductal stenting provides reasonable short-medium term palliation in duct-dependent cyanotic heart disease. Advances in surgical technique and post-operative care in the last two decades have led to improved survival and long-term outcome in children with complex cyanotic heart disease. Equally noteworthy, corrective surgery is increasingly performed at an earlier age and a lower body weight, obviating the need for palliative procedures in lesion-like Tetralogy of Fallot (TOF) in the more established centers. However, palliative Blalock Taussig (BT) shunt is commonly performed today in relatively complex duct-dependant lesions. Many of these conditions require staged palliation or can only be corrected at a later age. Hearts with single-ventricle physiology with pulmonary atresia and TOF with pulmonary atresia (TOF-PA) are examples of such conditions. Thus, in the modern era, BT shunt as a palliation is an operation that is almost exclusively performed in the neonatal period or early infancy.Ductus arteriosus stenting, although not widely accepted, is nevertheless attractive as a less invasive alternative for first-stage palliation.–4 The foMost of these patients are neonates or very young infants in whom the ducts are maintained open by PGE1 infusion. Our preference is to turn off the infusion the night before the procedure. The purpose of this is to have a reasonably constricted ductus arteriosus at the time of the procedure as ducts that are large (≥2.5 mm) will not be suitable for stenting. There would be a high risk of stent migration in such large ducts. However, a small number of patients cannot tolerate even a few hours without PGE1 infusion. In such cases, the PGE1 may be turned off just before or at the beginning of the procedure.We prefer that the procedure is done under general anaesthesia and special attention be given to minimize hypothermia. Bowls of saline for flushing and contrast media should be kept in a basin of warm water throughout. It is highly recommended that an arterial line and a central venous line be secured after induction of anaesthesia for monitoring and administration of drugs during and after the procedure.For the procedure itself, one femoral artery is cannulated with a 4-F sheath and one vein is accessed with 5-6 F sheath. Heparin 50 units/kg is given at the start of the procedure and repeated every 1-1½ hour. Baseline measurements of arterial blood pressure, central venous pressure (CVP) and blood gases are done.Extrapolating from adult practice in coronary stenting, starting antiplatelet agent(s) a day before the procedure may be a worthwhile measure to prevent acute thrombosis, but convincing data would not be forthcoming given the low numbers of this procedure.In most of the patients, the diagnosis would have been established by echocardiography. The role of angiography is to have a detailed evaluation of the ductus arteriosus morphology. As opposed to isolated persistence of the ductus arteriosus, in duct-dependent cyanotic congenital heart disease (CHD), the ductus arteriosus is markedly varied with regards to its origin from the aorta, size and shape, length, tortuosity and its insertion onto the pulmonary artery .5] The  The 5] TIt is thus crucial that the initial angiographic study gives adequate information with regards to where the ductus arises from the aorta, its shape, course and tortuosity, its site of insertion onto the pulmonary artery, presence of branch pulmonary artery stenosis (stenoses), especially those that insert onto the LPA. The projections that are most helpful are the straight lateral and the “4-chamber” view  to open up the pulmonary artery bifurcation and show the proximal LPA stenosis if this is present .From these angiograms, measurements of the narrowest part of the ductus , the size of the ampulla, the body of the ductus for the long tubular type and diameters of the branch pulmonary arteries are made.As elaborated above, our exclusion criteria are ductuses that are not sufficiently constricted at the pulmonary end (≥2.5 mm) because of the risk of stent migration and those in whom there is pre-existing branch pulmonary artery stenosis at the site of ductal insertion, especially in hearts with single-ventricle physiology.Our approach to ductal stenting is based largely on ductal morphology, particularly on how the ductus arises from the aorta. In the foregoing, we describe four broad techniques that would cover the vast majority of ductus arteriosus morphology, which are suitable for stenting. The group A ductus is the most amenable to stenting, the procedure generally being straightforward and the least likely to develop branch PA stenosis in the medium term. The first technique (A) is described in a detailed step-by-step manner including choice of guidewire, stent size and length, positioning and expansion of stent. Some aspects of this, such as repeated hand injections for accurate positioning, are also integral to the other techniques and they will not be repeated. The catheters, guidewires, balloon and stents that are deemed essential for the procedure are listed in These ductus arteriosus are seen more in PAIVS, critical pulmonary stenosis (PS) and tricuspid atresia. They often resemble the commonest form of isolated PDA, the Krichenko type A, i.e., having a wide ampulla and tapering down to a tight constriction. It ariseOnce preliminary angiograms have been performed with a 4-F pigtail catheter, the short 4-F sheath is replaced with a 4-F long sheath (Cook's). The tip of the long sheath is placed just below the ductal ampulla. A 4-F Judkins' Right (JR) catheter is maneuvered into the ampulla and a hand injection is done under fluoroscopy to guide the crossing of ductus. A 0.014″ coronary wire is used to cross the ductus and enter into the pulmonary artery. It is important to have a Y-connector (Tuohy Borst) secured at the hub of the catheter to prevent blood loss as the JR has a 0.035″ lumen. Our choice of wire is the choice PT extra support (Boston Scientific) as it has a short, floppy hydrophilic tip for negotiating the constriction and distal tortuosity if present and a relatively stiff body to enable tracking of balloon-stent across the ductus. The floppy tip and a sufficient length of the stiff body should be anchored securely in a distal branch pulmonary artery. Repeat the angiograms using small volume of contrast with hand injection via the side-port of the long sheath, in the straight lateral and four-chamber projections for measurements of the ductus. The guidewire across the ductus tends to straighten it. A more accurate measurement of the length of the ductus for selection of stent length is made (In this type of ductus not much “straightening” occurs with placement of guidewire as in the more tortuous forms).For patients weighing 3.0-4.0 kg, we choose a 4.0-mm diameter stent and for those weighing 4.0-5 kg, we would use a 4.5-mm diameter stent. For patients weighing <3.0 kg, we would choose a 3.5-mm diameter stent. Patients below 2.5 kg should be excluded as the 4-F long sheath may cause major damage to the femoral artery. The stent length chosen should ideally cover the entire ductus, expecting that 15-20% shortening will occur upon full expansion. We use pre-mounted stents in all cases.To prevent displacement of stent from balloon during insertion of the balloon-stent ensemble into the long sheath, the distal tip of short 4-F sheath used previously for the pigtail angiograms is cut and used to protect the stent as it is being pushed across the rubber valve. As the stent is advanced towards the ampulla, it is necessary to ensure that the guidewire remains as straight and taut as possible. Once the tip of the stent is across the narrowest part of the ductus , hand injections are repeated in the same projections and fine adjustments are made to position the stent accurately, such that enough stent length is in the main pulmonary artery and secondly there is no protrusion into the aorta at the other end. Stents protruding into the aorta may be difficult to re-cross at follow-up catheterization. Once satisfied with the positioning, the assistant inflates rapidly while the operator keeps the balloon catheter fixed and steady as the stent tends to jump forward during inflation (“melon-seeding”). Once fully expanded, the balloon is deflated and angiograms are repeated . It is iThese ducts are most commonly seen in TOF-PA, as well as more complex forms of cyanotic heart disease such as TGA-VSD-PA or hearts with single-ventricle physiology. They arise from the underside of the arch opposite the origin of the left subclavian artery (LSCA) or its equivalent in a right aortic arch. The ductus tapers down vertically and often forms a kink as it inserts onto the pulmonary artery in a tight constriction. Quite commonly, it inserts onto the proximal part of the LPA in a left aortic arch . KinkingThis type of ‘vertical’ ductus arteriosus generally is not amenable to stenting via the retrograde, femoral artery route as it is very difficult to engage the ampulla, and even more so, securing a stable guidewire position for tracking of balloon-stent ensemble. Unless one is familiar with axillary artery cannulation or carotid artery cut-down, stenting of this type of ductus may be achieved by the transvenous route except in hearts with single-ventricle physiology . A 5-F JIn this group, the ductus arteriosus arises more proximally than those in isolated persistent ductus arteriosus, but not as extreme as in group (B). They arise from the side opposite the origin of the LSCA; hence, a less vertical take-off than in group (B) ductus. These ducts tend to be long and tubular with a more tortuous course especially near its insertion onto the pulmonary artery . In geneAs in (A), after the preliminary angiograms with a 4-F pigtail catheter, a 4-F long sheath is placed in the aorta with its tip near the ductal ampulla. However, instead of a 4-F JR catheter, a 4-F pigtail with its tip cut off to form an inverted J, is often required to engage the ductal ampulla and perform selective angiograms of the ductus and pulmonary arteries. Due to its tortuosity and tight constriction at its pulmonary end, crossing it with choice PT extra-support may be very difficult or not possible. The BMW wire (Abbott Vascular) or others with a similar degree of floppiness are preferred. The tip of the wire is gently advanced through the ductus while simultaneously twisting it clockwise and anti-clockwise with a torquer. This may require several attempts as the tortuosity may force the wire tip to spring out the ductus. Once a good length of the wire is in the pulmonary artery and securely anchored, the tortuosity tends to straighten out and the ductus takes a more horizontal orientation. Repeat hand-shot angiograms via the side-port of the long sheaths in the projections above will show this well and this should be the basis of measurements for choice of stent length. The rest of the procedure is as in (A).Occasionally, the balloon-stent ensemble may not be able to track the softer BMW wire across the ductus. The balloon-stent should be taken out and a second, stiffer wire (Choice PT extra-support) may now be able to cross the straightened-out ductus. The BMW wire is then removed and the balloon-stent is tracked over the new wire, repeating the steps as in (A) above .In this least common of ductus arteriosus, comprising less than 5%, the ductus has the peculiar appearance of a BT shunt. The long tubular ductus arises from the left subclavian artery (LSCA) (or from the right subclavian artery in a right aortic arch) and joins the pulmonary artery in a roughly perpendicular fashion. There is usually a tight constriction at the site of pulmonary insertion. Stenting this type of ductus can be approached by the retrograde trans-arterial method as described in (A) above. The tip of a 4-F long sheath is placed near the origin of the LSCA. A 4-F JR catheter is used to engage the proximal part of the LSCA, through which an extra-support choice PT wire is used to cross the ductus and anchored deeply in a branch pulmonary artery. As described above, measurements for selection of stent length are best made with angiograms after guidewire positioning. With long tubular duct, a single long stent is likely to have great difficulty in tracking the wire. It is best to place a short stent in the distal part of the ductus to cover just enough of the ductal constriction and a second stent for the proximal part .This is not a common complication, perhaps a rate of 2-3% can be expected as more procedures are performed, but it is very serious and life threatening. It presents in a dramatic fashion and requires immediate action. Typically, the oxygen saturation reaches normal or near normal level immediately after stent expansion. In the few cases encountered, the oxygen saturation fell rapidly as preparations were made to wrap up the procedure. Angiography typically reveals thrombus occluding stent completely or partially . If the Fortunately, this is an uncommon complication (<1%) even in those ductuses that are severely constricted at the pulmonary end. It tends to occur with manipulation of guidewire and placement across the ductus. This is manifested by sudden deterioration in oxygenation as one is preparing the balloon-stent. If the guidewire is well positioned, it is a matter of rapidly going through the steps of stent implantation. However, if this occurs only at the stage of guidewire manipulation into the ductus, it is best to remove the wire and re-start the PGE1 infusion, recommencing the procedure after a period of stabilization. If the problem recurs, it is best to abandon the procedure and send the patient to surgery. Given its very low occurrence, it is not possible to predict which patient is likely to develop this complication. It is advisable to have the PGE1 infusion on standby in the catheterization laboratory.This is not a life-threatening complication, but nonetheless serious as the patient needs to go to surgery semi-electively for stent removal and construction of a BT shunt. This is likely to occur if the pulmonary end of the ductus is not sufficiently constricted (>2.5 mm). It is advisable not to proceed with catheterization and leave the patient without PGE1 infusion for a longer period if the patient is only mildly cyanosed and has evidence of significantly large ductal flow clinically and on echocardiography. Once an expanded stent has migrated to the pulmonary artery, it is not possible to remove it except surgically. .If stable hemodynamically, the patient is transferred to the ICU and kept ventilated for at least 12 h with arterial and central venous lines. It is common to have high, near-normal oxygen saturations in the first 48-72 h, but this is often well tolerated. Clinically severe heart failure from overshunting is uncommon and the patient should be extubated as early as possible. Heparin at 25 units/kg/h should be continued for 72 h and aspirin may be started the next day . Discharge and follow-up review are as per patients following creation of BT shunt. The durability of palliation by ductal stenting is generally less compared to that of surgical shunt; hence, a close follow-up is required and the definitive surgery should be planned within 6-18 months of ductal stenting. Re-crossing the stented ductus at follow-up catheterization, especially where a long stent was implanted and significant in stent stenosis has occurred, may be difficult. It is important to stent the entire length of the ductus as much as possible. There is a tendency for the unstented part of the ductus to become stenosed rapidly .Ductal stenting is a reasonable, less invasive alternative to BT shunt as first-stage palliation in neonates with duct-dependant cyanotic CHD. Crucial to the success of the procedure and medium-term outcome is case selection and choice of technique. This is largely based on the angiographic morphology of the ductus - its origin from the aorta, shape, length and size, tortuosity and its insertion onto the pulmonary artery.


A method is more important than a discovery, since the right method will lead to new and even more important discoveries.Lev D. Landau, Nobel Prize laureate-Molecular Cytogenetics. We are proud to introduce you to a new home for biomedical research focused on all aspects of chromosome biology and applications of molecular cytogenetic techniques in all areas of biomedicine. Molecular Cytogenetics [Molecular Cytogenetics will be a valuable resource for researchers all over the world, both those who are already experts and those entering the field.Welcome to genetics  represenMolecular Cytogenetics will provide multilateral coverage of numerous applied and basic aspects of current biomedicine.Molecular cytogenetics comprises a set of the techniques operating with either the entire genome or with specific DNA sequences to study genome structure and functions at the chromosomal level. Molecular cytogenetics can also be defined as a specific focus of biomedical sciences targeted at studying chromosomes at molecular and single-cell resolutions and at all stages of the cell cycle. Furthermore, the area of molecular cytogenetic technique applications has come to encompass almost everything from applied research in clinical and cancer genetics to basic studies in cellular and structural biology, genomics, genetics, and neurosciences. Thus, a journal focused on molecular cytogenetics is not limited to technical issues but will also address advances in current biomedical research. Taking into account the growing amount of biomedical journals available, one can argue whether we need another one. However, any scientist working on theoretical and practical aspects of chromosome biology would undoubtedly agree that there are few journals covering this area of biology, and that there are no journals providing immediate open access. We performed an informal analysis Figure  that shoMolecular Cytogenetics fills another gap in current biomedical publishing.Molecular cytogenetics is a rapidly evolving field of biomedicine. Throughout the last decade, significant breakthroughs in molecular cytogenetics have been made. This can be attributed in part to the establishment of new composite molecular cytogenetic technologies that have significantly enhanced diagnosis in medical and cancer genetics, for example the conception of molecular karyotyping using microarray (array-CGH) and more sophisticated digital karyotyping for identification of subtle genomic imbalances and copy number changes at molecular resolutions. New technologies are expected to follow at this rapid pace. Molecular cytogenetic techniques possess the potential not only to become more efficient through further enhancements and modifications, but also to lead to new and important discoveries in biomedicine. In this context, the lack of a journal exclusively dedicated to molecular cytogenetics can be considered an omission. Therefore, Molecular Cytogenetics aims to become a significant international participant in the fields of genetics and cell biology. The purpose of the journal is, therefore, to publish timely and high-quality articles concerning chromosome biology and the application of molecular cytogenetic techniques in all areas of biomedicine. To achieve this, the Editorial Board of Molecular Cytogenetics gathers well-known experts from all over the world [Molecular Cytogenetics, the Editors-in-Chief or corresponding specialists from the Editorial Board will immediately screen a submission and appropriate manuscripts will be sent for peer review to two independent reviewers. Based on their reports and scoring, a final decision will be made regarding acceptance of the manuscripts. Editors-in-Chief reserve the right to make final decisions concerning each manuscript submitted to the journal. At first sight our peer review system does not significantly differ from that proposed by other journals. However, we encourage our Editorial Board members as well as reviewers to be motivated critical advisers for improving a manuscript rather than rigorous censors for biomedical publishing, which is unfortunately a common experience for anyone who has ever tried to publish his or her original research results.he world . To makeMolecular Cytogenetics is published by the open access publisher, BioMed Central [Molecular Cytogenetics is that there are no limitations regarding space or color figures. Central . BioMed  Central , whereby Central . WaiversMolecular Cytogenetics possesses, we believe the journal to be of great benefit to the field of biomedicine. We invite you to work together with us to create this new and high-visibility open-access forum for the biomedical sciences.Considering all the advantages Molecular Cytogenetics, IYI is the managing editor, and SGV is a member of the Editorial board. The authors declare that they have no competing interests.YBY, TL, and LGS are the Editors-in-Chiefs of


Dopamine is a catecholamine that is used as a neurotransmitter both in the periphery and in the central nervous system. Dysfunction in various dopaminergic systems is known to be associated with various disorders, including schizophrenia, Parkinson's disease, and Tourette's syndrome. Furthermore, microdialysis studies have shown that addictive drugs increase extracellular dopamine and brain imaging has shown a correlation between euphoria and psycho-stimulant-induced increases in extracellular dopamine . These cWe construct a mathematical model of dopamine synthesis, release, and reuptake and use it to study homeostasis in single dopaminergic neuron terminals. We investigate the substrate inhibition of tyrosine hydroxylase by tyrosine, the consequences of the rapid uptake of extracellular dopamine by the dopamine transporters, and the effects of the autoreceoptors on dopaminergic function. The main focus is to understand the regulation and control of synthesis and release and to explicate and interpret experimental findings.We show that the substrate inhibition of tyrosine hydroxylase by tyrosine stabilizes cytosolic and vesicular dopamine against changes in tyrosine availability due to meals. We find that the autoreceptors dampen the fluctuations in extracellular dopamine caused by changes in tyrosine hydroxylase expression and changes in the rate of firing. We show that short bursts of action potentials create significant dopamine signals against the background of tonic firing. We explain the observed time courses of extracellular dopamine responses to stimulation in wild type mice and mice that have genetically altered dopamine transporter densities and the observed half-lives of extracellular dopamine under various treatment protocols.Dopaminergic systems must respond robustly to important biological signals such as bursts, while at the same time maintaining homeostasis in the face of normal biological fluctuations in inputs, expression levels, and firing rates. This is accomplished through the cooperative effect of many different homeostatic mechanisms including special properties of tyrosine hydroxylase, the dopamine transporters, and the dopamine autoreceptors. Dopamine is a catecholamine that is used as a neurotransmitter both in the periphery and in the central nervous system (CNS)-4. ImporDopamine is known to play an important role in many brain functions. Dopamine affects the sleep-wake cycle , it is cDysfunction in various dopaminergic systems is known to be associated with various disorders. Reduced dopamine in the pre-frontal cortex and disinhibited striatal dopamine release is seen in schizophrenic patients . Loss ofIn this paper we construct a mathematical model of dopamine synthesis, release, and reuptake and use it to study homeostasis in single dopaminergic neuron terminals. It is known that the enzyme tyrosine hydroxylase (TH), the rate limiting enzyme in dopamine synthesis, has the unusual property of being inhibited by its own substrate, tyrosine . Cytosoll-dopa) by tyrosine hydroxylase (TH) and l-dopa is converted into cytosolic dopamine (cda) by aromatic amino acid decarboxylase (AADC). Cytosolic dopamine is transported into the vesicular compartment by the monoamine transporter and vesicular dopamine (vda) is released from the vesicular compartment into the extracellular space at a rate proportional to the firing rate of the neuron. In the extracellular space, extracellular dopamine (eda) affects the autoreceptors, is taken up into the terminal by the DATs and is removed from the system by uptake into glial cells and the blood and diffusion out of the striatum. Dopamine is also catabolized both in the terminal and in the extracellular space.A schematic diagram of the model is indicated in Figure et al. eda means data in , figure Km of the transporter in the literature range  of the cellular dopamine is in the vesicular compartment. The vesicles take up a significant fraction of the volume terminal, perhaps 1/4 to 1/3 (reference). For simplicity we are assuming that the vesicular compartment is the same size as the non-vesicular cytosolic compartment. This assumption is unimportant since we take the cytosol to be well-mixed and we are not investigating vesicle creation, movement toward the synapic cleft, and recyling where geometry and volume considerations would be crucial.After dopamine is synthesized it is packaged into vesicles by the vesicular monoamine transporter, MAT. We take the ments in  and the ments in  suggest vda, is put into the synaptic cleft, where it becomes eda, by the term fire(t)(vda) in the differential equations for vda and eda (see above). fire is a function of time in some of our in silico experiments, for example in Results G where we investigate individual spikes. However, for most of our experiments fire = 1 μM/hr, which means that vesicular dopamine is released at a constant rate such that the entire pool turns over once per hour. This is consistent with a variety of experimental results on turnover and we will see in Results C that this choice gives decay curves after α-methyl-p-tyrosine (α-MT) inhibition of TH that match well the findings of Caron and co-workers  an an25] anVmax to zero), we see changes in steady state values that are qualitatively similar to those seen in  an an25] aneda after stimulation. In the model we can test this directly by raising the concentration of eda at time T = 0 to 10 times normal (for either WT or DAT-/-) and measuring the half-life of eda as the system relaxes back to equilibrium. See Figure One important focus of the experiments in , 25] an an25] aneda for WT mice is .067 seconds and the half-life for DAT-/- mice is approximately 6 seconds, giving a ratio of DAT-/- half-life to WT half-life of about 90. Caron and coworkers find similar numbers experimentally except that their ratio is about 300. We note that the ratio is sensitive, of course, to small changes in the small WT half-life that is determined both in experiments and in the model from a very steep curve.We find in the model that the half-life of eda in WT, DAT-/-, DAT-/-, and DAT-tg mice in response to pulse stimulation. Panel A of Figure +/-) lowers the eda peak compared to wild-type. Our investigations show that this behavior is due to two competing effects.Some of the most interesting experiments in ,25 and  measure Vmax of the transporter. We increased the Vmax by 50% for DAT-tg mice compared to wild type, decrease it by 50% for DAT+/- mice, and decrease it to zero for DAT-/- mice. However, vda, the pool available for release, has the following model values: vda = 98.9 μM (DAT-tg), vda = 81 μM (WT), vda = 59 μM (DAT+/-), vda = 11.4 μM (DAT-/-). In the model, the amount of dopamine released in response to a pulse small enough not to deplete the vda pool very much is proportional to vda. Thus more dopamine is released in DAT-tg compared to WT compared to DAT+/- compared to DAT-/-. If this were the only effect then one would expect the eda peak to be highest for DAT-tg, lower for WT, still lower for DAT+/-, and lowest for DAT-/-.The first effect is that the amount of dopamine available to be released in response to an external pulse is not strictly proportional to the number of DATs. In the model "the number of DATs" is represented by the eda back into the cell faster. Thus, if the amount released were the same in each case, we would expect the eda peak to be lowest for DATtg, somewhat higher for WT, still higher for DAT+/-, and highest for DAT-/-. However, as we have seen, the amount released is not the same but decreases as one progresses from DAT-tg to WT to DAT+/- to DAT-/-. These are the two competing effects that determine the heights of the peaks. The situation is even more complicated and interesting, however. The Km for the DAT has been measured in a number of experiments. A reasonable range of possible values is 0.2 μM to 2 μM; see eda back  μM; see  and 74]eda back Km = 0.2 μM. Notice that the peaks decrease as one goes from DATtg to WT to DAT+/- to DAT-/-. In each case the amount of stimulation was the same. This is what one would expect if the first effect, the amount of dopamine released, dominates. To test whether the saturation of the DATs causes this effect we did a model experiment in which the amount of stimulation was reduced to 1/10 of what it was before. The results can be seen in Panel C of Figure +/-. Note also how much narrower the peaks are because the DATs are operating on the linear parts of their response curves rather than the saturation part. Panels B and C show that the peaks can be either decreasing or increasing as one proceeds from DAT-tg to WT to DAT+/-, depending only on the amount of stimulation. The DAT-/- peak remains lowest because it is not affected by saturation effects on the DATs, since there aren't any.In Panel B of Figure Km of the DATs we will decrease the saturation effects seen in Panel B of Figure Km of the DATs has been raised to 1.6 μM and everything else remains the same as in the model experiments shown in Panel B. Now the WT peak is higher than both the DAT-tg peak and the DAT+/- peak. The differences are not great, but the non-monotone effect is clear. As before, the DAT-/- peak is the lowest since so little dopamine is released.If we increase the Kms, and the amount of stimulation.These model experiments show that the relative heights of the peaks depend on the size of the vesicular stores, the number of DATs, their f denote the fraction of striatal terminals still alive. With 20 Hz stimulation, the peaks of the resulting eda curves are almost independent of f until f = .15  extracellular concentration of dopamine in the striatum by E(t). We'll ignore removal from the system and catabolism because we are interested in events on a very short time scale. Compared to the concentrations we get after stimulation, E starts very small, so we'll assume E(0) = 0. Assume that dopamine is released from the cells at a total rate of C/sec for to seconds. In [to = 2, so the concentration E(t) will satisfy the differential equation:Bergstrom and Garris do not explain the reasons why the two cases (20 Hz and 60 Hz) are so different, although the reasons are implicit in their discussions. We give an explanation here using a simple model for duced in . As we wonds. In , to = 2,Km = 0.2 μM as in our large model. For t > 2 the C isn't there any more but that doesn't affect the maximum concentration of E(t), which occurs at t = 2. We want to calculate E(2) and then introduce our scale factor f and see how the value scales with f.where we take μM. Since the concentrations are below Km we can approximate (1) by:We will consider two cases. Suppose the release is relatively low as it is in the 20 Hz case where the peak concentrations are (on average) between 0.1 and 0.2 We easily solve this differential equation and findf of cells are still alive. Then C is replaced by fC and Vmax is replaced by fVmax, so the maximum is:Suppose, now, that only the fraction f depends on the size of Vmax close to 4 μM/sec and Km = 0.2 μM, so E(2) will be almost constant as f gets smaller from 1. Only when f gets very very small will E(2) plunge down to zero. This is the constant behavior of the peaks seen in [The shape of the graph of E(2) as a function of  seen in , figure μM for the intact striatum, far above the Km of the transporters. As long as the concentrations are well above the Km the transporters are saturated and we can approximate (1) byIn the case of 60 Hz stimulation the peaks are quite high, as much as 3 t = 2 is:so the solution at f of cells are left, then,If only the fraction f and that's what Bergstrom and Garris see in their figure Thus the maxima should decrease linearly with E stays well above Km. The complete behavior as f goes from 1 to 0 in the 60 Hz case should be: first, this linear decrease, then a middle range around the Km value where the rate of decrease is more modest, then a flat plateau as in the first case we considered, until, finally, E(2) should plunge to 0 for almost complete denervation. As the ability to take accurate voltametric measurements improves, it will be interesting to see if this prediction is correct.This calculation is correct as long as the concentration of It is well established that the expression levels of proteins vary substantially, even in genetically identical cells, and often vary substantially in time in individual cells . Some ofeda drops and downregulate TH when eda rises as it will do if the firing rate of the neuron increases [eda concentration provides feedback inhibition to TH. The strength of the effect can be seen in Panel B of Figure eda is graphed as a function of firing rate. The eda curve is much flatter in the presence of the autoreceptors. We note that the eda also affects firing rate directly via somatic autoreceptors [Autoreceptors on the presynaptic membrane upregulate tyrosine hydroxylase(TH) when ncreases ,61. Thuseceptors , but thiIt is known ,4 that teda [We see in our model responses that quite similar to those observed experimentally. Panel A of Figure eda . The modeda , figure eda to decline to an intermediate level, higher than normal but not as high as the short term response. The inhibition of TH by increased binding to the autoreceptors happens quickly, but the resulting decrease in cda and vda happens slowly over a nine hour period  contributed equally to the formulation of the model, the estimation of parameters, experimentation with the model, the biological interpretations and conclusions, and the writing and editing of the manuscript. All authors read and approved the final manuscript.


If this were the case, then the higher permeability of the BTB of peripheral tumor would be attributable to the presence of a greater number of pores in the BTB of peripheral tumors. In this study, we probed in vivo the upper limit of pore size in the BTB of rodent malignant gliomas grown inside the brain, the orthotopic site, as well as outside the brain in temporalis skeletal muscle, the ectopic site.The existence of large pores in the blood-tumor barrier (BTB) of malignant solid tumor microvasculature makes the blood-tumor barrier more permeable to macromolecules than the endothelial barrier of most normal tissue microvasculature. The BTB of malignant solid tumors growing outside the brain, in peripheral tissues, is more permeable than that of similar tumors growing inside the brain. This has been previously attributed to the larger anatomic sizes of the pores within the BTB of peripheral tumors. Since in the physiological state in vitro by scanning transmission electron microscopy. Following intravenous infusion of the respective Gd-dendrimer generations  the blood and tumor tissue pharmacokinetics of the Gd-dendrimer generations were visualized in vivo over 600 to 700 minutes by dynamic contrast-enhanced MRI. One additional animal was imaged in each Gd-dendrimer generation group for 175 minutes under continuous anesthesia for the creation of voxel-by-voxel Gd concentration maps.Generation 5 (G5) through generation 8 (G8) polyamidoamine dendrimers were labeled with gadolinium (Gd)-diethyltriaminepentaacetic acid, an anionic MRI contrast agent. The respective Gd-dendrimer generations were visualized The estimated diameters of Gd-G7 dendrimers were 11 ± 1 nm and those of Gd-G8 dendrimers were 13 ± 1 nm. The BTB of ectopic RG-2 gliomas was more permeable than the BTB of orthotopic RG-2 gliomas to all Gd-dendrimer generations except for Gd-G8. The BTB of both ectopic RG-2 gliomas and orthotopic RG-2 gliomas was not permeable to Gd-G8 dendrimers.in vivo the luminal fibrous glycocalyx of the BTB of malignant brain tumor and peripheral tumors is the primary impediment to the effective transvascular transport of particles across the BTB of malignant solid tumor microvasculature independent of tumor host site. The higher permeability of malignant peripheral tumor microvasculature to macromolecules smaller than approximately 12 nm in diameter is attributable to the presence of a greater number of pores underlying the glycocalyx of the BTB of malignant peripheral tumor microvasculature.The physiologic upper limit of pore size in the BTB of malignant solid tumor microvasculature is approximately 12 nanometers. In the physiologic state  The blood-tumor barrier (BTB) of malignant solid tumor microvasculature is more permeable to macromolecules than the endothelial barrier of normal tissue microvasculature of the continuous type,2. This Various sizes of pores have been identified in the BTB of malignant solid tumor microvasculature, which is discontinuous. These iin vivo with intra-vital microscopy after the intravenous infusion of particles in the nanometer size range labeled on the exterior with rhodamine, a cationic fluorescent dyet = predictive Gd concentration at time t min (mM)t = aebt+ cedt95% confidence intervals (CI) and root mean squared errors (RMSE) for best fit curve concentrations from the bi-exponential function [. The data in the table represent the statistical analysis for the orthotopic and ectopic RG-2 glioma Gd concentration curve profiles for the respective Gd-dendrimer generations over 600 to 700 minutes. A best fit was established for each Gd concentration curve profile as indicated by the corresponding low RMSE value. Note: 1 RMSE per profile.Click here for file


The fabrication of increasingly smaller machines to the nanometer scale can be achieved by either a “top-down” or “bottom-up” approach. While the former is reaching its limits of resolution, the latter is showing promise for the assembly of molecular components, in a comparable approach to natural systems, to produce functioning ensembles in a controlled and predetermined manner. In this review we focus on recent progress in molecular systems that act as molecular machine prototypes such as switches, motors, vehicles and logic operators. Typically a machine requires at least one moveable component that leads to the generation of work. A molecular or nano-scaled machine can therefore be defined as an ensemble of molecular components or devices assembled to achieve a specific level of mechanical work (output) as a consequence of an external stimuli (input) . Th7.In reviewing the current literature relating to molecular machine research we aimed to illustrate fundamental developments and progress relating to typical functions carried out by macroscopic machinery including transport, rotation and switching. While each of those alone does not create an artificial machine the progress does make a significant contribution to unlocking the key processes relating to control and function at the molecular level. Biological molecular machines far outweigh any artificially constructed machine both in complexity and function which will continue to inspire and challenge scientist for many years to come, one that will no doubt benefit through multi-disciplinary cooperation.


EHP is implementing new page charges of $30.00 per accepted manuscript page. This is a change from our former policy of charging by the printed journal page, and we hope authors will enjoy the benefit of receiving their page charge information earlier in the production process. In calculating page charges, we will include only text pages of the final accepted Microsoft Word version of the manuscript .Effective 1 August 2008, As of 1 August, we are also instituting a new policy of charging for color figures . For many years we have been proud to offer our authors free color printing; however, as a government publication, we must find ways to offset our expenses to ensure responsible stewardship of our federal funding. Therefore, authors henceforth will pay $500.00 for the first color figure and $100.00 for each additional figure. http://mc.manuscriptcentral.com/ehp and hope you will enjoy this improved submission system.Authors will still be billed for page and color charges, but bills will be sent earlier in the production process (soon after acceptance). We are pleased to offer our new Manuscript Central site at


The HR for KS declined steeply in the first months after HAART initiation and continued to be low 7–10 years afterwards . Thirty-three out of 52 (63.5%) KS cases among HAART users arose among PWHA who had stopped treatment or used HAART for less than 6 months.Between 1984 and 2006, 12 959 people with HIV/AIDS (PWHA) in the Swiss HIV Cohort Study contributed a total of 73 412 person-years (py) of follow-up, 35 551 of which derived from PWHA treated with highly active antiretroviral therapy (HAART). Five hundred and ninety-seven incident Kaposi sarcoma (KS) cases were identified of whom 52 were among HAART users. Cox regression was used to estimate hazard ratios (HR) and corresponding 95% confidence intervals (CI). Kaposi sarcoma incidence fell abruptly in 1996–1998 to reach a plateau at 1.4 per 1000 py afterwards. Men having sex with men and birth in Africa or the Middle East were associated with KS in both non-users and users of HAART but the risk pattern by CD4 cell count differed. Only very low CD4 cell count (<50 cells  At the beginning of the HIV epidemic, Kaposi sarcoma (KS) was one of the most common manifestations of AIDS . Follow-up visits take place every 6 months and all AIDS-defining events, including KS diagnosis and death, are recorded. The present study included PWHA enrolled up to 30 September 2005, and information recorded in the SHCS database up to 31 March 2006. People with HIV/AIDS were excluded from the present study if they (1) did not have information on date of birth, gender, or HIV transmission category (number (n)=54), (2) were diagnosed with KS at enrolment or earlier (n=368), or (3) had no follow-up visits (n=131).The SHCS is an ongoing study that has been enrolling people with HIV/AIDS (PWHA) over 16 years of age since 1988, with some retrospective enrolment going back to 1984, from seven large hospitals in Swiss cities  (vs other) was available only for 382 (64%) KS cases.A total of 597 KS cases were included in our present study: 545 were identified from the SHCS database, and 52 through record linkage with eight Swiss Cantonal Cancer Registries . Calendar period, HAART use, and months after HAART initiation and after treatment interruption were introduced as time-dependent variables.For each participant, person-years (py) at risk were calculated between enrolment and KS diagnosis, death, or last follow-up visit, whichever occurred first. Incidence rates per 1000 py were standardised for gender and age based on the enrolled population in the overall study period, using the direct method . Ninety-This study was approved by the local ethics committees of the collaborating SHCS clinics and of the International Agency for Research on Cancer.The present study included 12 638 PWHA who were KS-free at enrolment and among whom 597 incident KS cases were identified . Fifteen per cent of PWHA had AIDS at enrolment and an additional 3119 (24.7%) developed it during follow-up. Among the latter, KS was the AIDS-defining illness in 268, whereas 329 KS cases developed in PWHA who had already manifested another AIDS-defining illness.vs ⩾350 cells μl−1, 12.85; 95% CI, 9.59–17.23). These associations were also present, but were weaker, among HAART users with the exception of the association with place of birth that became stronger . In contrast with non-users, no change in the HR for KS was seen among HAART users with CD4 cell counts in the range of 50–⩾350 cells μl−1 and the only significant risk increase was found for CD4 cell count less than 50 cells μl−1 at enrolment . On account of the rarity of KS among HAART users, HRs showed, however, broad CIs (A large proportion (48.4%) of available py derived from HAART users and road CIs .μl−1  (data not shown) was even more strongly associated with KS risk than CD4 cell count at enrolment. Furthermore, KS risk was greatly increased among PWHA who had stopped using any antiretroviral drugs for at least 3 months   . AdditioSkin was reported as the presentation site in the majority of KS cases (74.3%). Temporal trends and associations with HAART use and CD4 cell count  did not differ by KS presentation site (data not shown).μl−1 at KS onset while on HAART for ⩾6 months); and (4) none of the above (data not shown). Eighteen (34.6%) KS cases had not been taking any antiretroviral drug for 3 months or more, and in 10 instances for 12 months or longer. Recent initiation of HAART was identified in 15 KS cases, among whom five of the nine KS were from Africa/Middle East. Severe immunodeficiency was identified among 10 KS cases. Nine KS cases, all from the MSM transmission category, could not be assigned to any of the three categories above. Five of them  had a CD4 cell count ⩾400 cells μl−1  at KS diagnosis.Finally, the 52 HAART users who developed KS were individually reviewed and classified into the following groups: (1) no antiretroviral drug in the 3 months before KS diagnosis; (2) recent initiation of HAART (<6 months before KS diagnosis); (3) severe immunodeficiency . The proportion of SHCS participants with CD4 cell counts <350 cells μl−1 who had never been treated was small (<3%) in 2006 in all HIV transmission categories. Despite the widespread use of HAART and the introduction after 1996 of successively more potent antiretroviral drugs, KS incidence in the SHCS seems to have reached a plateau after 2001, as reported among AIDS patients in the United States  than on KS, and, hence, non-Hodgkin's lymphoma incidence  became higher than KS incidence among HAART users .Weaknesses of our study are the lack of information on year of HIV seroconversion and on the presence of KS herpesvirus co-infection. Furthermore, we evaluated HAART use by intention-to-treat, that is, without subtracting all periods where treatment had been stopped, so its efficacy may be underestimated. A major strength of our cohort study is that it is the largest ever reported with respect to the number of KS cases and the number of person-years of HAART use. Furthermore, the representativeness of the SHCS with respect to Swiss PWHA was especially good (i.e., inclusion of 49% of all HIV-positive people and 67% of all AIDS cases in the country,


Previous lesion, electrical self-stimulation and drug addiction studies suggest that the midbrain dopamine systems are parts of the reward system of the brain. This review provides an updated overview about the basic signals of dopamine neurons to environmental stimuli.The described experiments used standard behavioral and neurophysiological methods to record the activity of single dopamine neurons in awake monkeys during specific behavioral tasks.Dopamine neurons show phasic activations to external stimuli. The signal reflects reward, physical salience, risk and punishment, in descending order of fractions of responding neurons. Expected reward value is a key decision variable for economic choices. The reward response codes reward value, probability and their summed product, expected value. The neurons code reward value as it differs from prediction, thus fulfilling the basic requirement for a bidirectional prediction error teaching signal postulated by learning theory. This response is scaled in units of standard deviation. By contrast, relatively few dopamine neurons show the phasic activation following punishers and conditioned aversive stimuli, suggesting a lack of relationship of the reward response to general attention and arousal. Large proportions of dopamine neurons are also activated by intense, physically salient stimuli. This response is enhanced when the stimuli are novel; it appears to be distinct from the reward value signal. Dopamine neurons show also unspecific activations to non-rewarding stimuli that are possibly due to generalization by similar stimuli and pseudoconditioning by primary rewards. These activations are shorter than reward responses and are often followed by depression of activity. A separate, slower dopamine signal informs about risk, another important decision variable. The prediction error response occurs only with reward; it is scaled by the risk of predicted reward.Neurophysiological studies reveal phasic dopamine signals that transmit information related predominantly but not exclusively to reward. Although not being entirely homogeneous, the dopamine signal is more restricted and stereotyped than neuronal activity in most other brain structures involved in goal directed behavior. Results from lesion and psychopharmacological studies suggest a wide range of behavioral functions for midbrain dopamine systems. The key question is, which of these many functions are actively encoded by a phasic dopamine signal compatible with rapid neuronal mechanisms? Good hints come from drug addiction and electrical self-stimulation, suggesting that dopamine activity has rewarding and approach generating effects ,2.We can define rewards as objects or events that generate approach and consummatory behavior, produce learning of such behavior, represent positive outcomes of economic decisions and engage positive emotions and hedonic feelings. Rewards are crucial for individal and gene survival and support elementary processes such as drinking, eating and reproduction. This behavioral definition attributes reward function also to certain nonalimentary and nonsexual entities, including money, technical artefacts, aesthetic stimulus attributes and mental events. Rewards engage agents in such diverse behaviors as foraging and trading on stock markets.Rewards have specific magnitudes and occur with specific probabilities. Agents aim to optimize choices between options whose values are determined by the kind of the choice object and its magnitude and probability . TherefoPredictions are of fundamental importance for making informed decision by providing advance information about the available choice options, as opposed to guesses that occur when outcomes are unknown. As reward can be quantified by probability distributions of value, reward predictions specify the expected value and (expected) variance or standard deviation of the distribution.Evolutionary pressure favors the energy efficient processing of information. One potential solution is to store predictions about future events in higher brain centers and calculate in lower brain centers the difference between new environmental information and the stored prediction. The discrepancy between the actual event and its prediction is called an event prediction error. Keeping up with the changing environmental situation by higher brain centers would simply involve updating the predictions with the less information containing, and less energy consuming, prediction errors rather than processing the full peripheral information every time one little thing has changed . In thisAnimal learning theory and efficient temporal difference reinforcement models postulate that outcome prediction errors are crucial for Pavlovian and operant conditioning ,6. CurreThe majority of midbrain dopamine neurons 75-80%) show rather stereotyped, phasic activations with latencies of <100 ms and durations of <200 ms following temporally unpredicted food and liquid rewards Figure . This bu0% show rThe dopamine response to reward delivery appears to code a prediction error; a reward that is better than predicted elicits an activation (positive prediction error), a fully predicted reward draws no response, and a reward that is worse than predicted induces a depression (negative error) -24. ThusThe error response varies quantitatively with the difference between the received reward value and the expected reward value -23. The Thus, dopamine neurons respond to reward only to the extent to which it differs from prediction. As prediction originates from previously experienced reward, dopamine neurons are activated only when the current reward is better than the previous reward. The same reward over again will not activate dopamine neurons. If the activation of dopamine neurons has a positively reinforcing effect on behaviour, only increasing rewards will provide continuing reinforcement via dopaminergic mechanisms. This may be one reason why constant, unchanging rewards seem to lose their stimulating influence, and why we always need more reward.Animal learning theory has developed formal paradigms for testing reward prediction errors. In the blocking test , a stimuThe conditioned inhibition paradigm  offers aThe results from these two formal tests confirm that dopamine neurons show bidirectional coding of reward prediction errors.In a general sense, a reward predicting stimulus specifies the value of future rewards by informing about the probability distribution of reward values. Thus, the stimulus indicates the expected value (first moment) and (expected) variance (second moment) or standard deviation of the distribution.The dopamine value prediction error response is sensitive to both the first and second moments of the predicted reward distribution at two seconds after the stimulus. In an experiment, different visual stimuli can predicted specific binary probability distributions of equiprobable reward magnitudes with different expected values and variances. As the prediction error response reflects the difference between the obtained and expected reward value, the identical magnitude of the received reward produces either an increase or decrease of dopamine activity depending on whether that reward is larger or smaller than its prediction, respectively . This reThe dopamine coding of reward value prediction error adapts to the variance or standard deviation of the distribution. In a binary distribution of equiprobable rewards, the delivery of reward with the larger magnitude within each distribution elicits the same dopamine activation with each distribution, despite 10 fold differences between the obtained reward magnitudes  . NumericDopamine neurons show activations ('excitations') following reward predicting visual, auditory and somatosensory stimuli Figure  31-33].-33.31-33During the course of learning, the dopamine activation to the reward decreases gradually across successive learning trials, and an activation to the reward predicting stimulus develops at the same time ,37. The The objective measurement of subjective reward value by choice preferences reveals that rewards lose some of their value when they are delayed. In fact, rats, pigeons, monkeys and humans often prefer sooner smaller rewards over later larger rewards -42. ThusPsychometric measures of intertemporal behavioral choices between sooner and later rewards adjust the magnitude of the early reward until the occurrence of choice indifference, defined as the probability of choosing each option with p = 0.5. Thus, a lower early reward at choice indifference indicates a lower subjective value of the later reward. In our recent experiment on monkeys, choice indifference values for rewards delayed by 4, 8 and 16 s decreased monotonically by about 25%, 50% and 75%, respectively, compared to a reward after 2 s . The decThe dopamine responses to reward predicting stimuli decreases monotonically across reward delays of 2 to 16 s ,43, despThus, dopamine neurons seem to code the subjective rather than the physical, objective value of delayed rewards. Given that utility is a measure for the subjective rather than objective value of reward, the response decrease with temporal discounting might suggest that dopamine neurons code reward as (subjective) utility rather than as (objective) value. Further experiments might help to test utility coding more directly.Aversive stimuli such as air puffs, hypertonic saline and electric shock induce activating ('excitatory') responses in a small proportion of dopamine neurons in awake animals . The deAlthough some dopamine neurons are activated by aversive events, the largest dopamine activation is related to reward. Data obtained with other methods lead to similar conclusions. Fast scan voltammetry in behaving rats shows striatal dopamine release induced by reward and a shift to reward predicting stimuli after conditioning , suggestStimuli can induce alerting and attentional reactions when they are physically important  or when they are related to reinforcers . Behavioral reactions to salient stimuli are graded by the physical intensity of the stimuli and the value of the reinforcer, respectively. Physical salience does not depend on reinforcement at all, and motivational salience do not depend on the valence of the reinforcers (reward and punishment).Physically intense visual and auditory stimuli induce activations in dopamine neurons Figure . These rThe activations to physically salient stimuli do not seem to reflect a general tendency of dopamine neurons to be activated by any attention generating event. In particular, other strong attention generating events such as reward omission, conditioned inhibitors and aversive stimuli induce predominantly depressions and rarely genuine dopamine activations ,29. ThusOther stimuli induce activations in dopamine neurons without apparent coding of reward value. These activations are smaller and shorter than the responses to reward predicting stimuli and are often followed by depression when the stimuli are unrewarded Figure .Dopamine neurons show activations following control stimuli that are presented in pseudorandom alternation with rewarded stimuli ,29,32. TDopamine neurons show a rather stereotyped initial activation component to stimuli predicting rewards that occur after different delays . The iniDopamine neurons show frequent activations following conditioned aversive stimuli presented in random alternation with reward predicting stimuli; the activations disappear largely when different sensory modalities are used (65% vs. 11% of neurons ), suggesThe reasons for these different dopamine activations might lie in generalization, pseudoconditioning or motivational stimulus salience. Generalization arises from similarities between stimuli. It might explain dopamine activations in a number of situations, namely the activations to unrewarded visual stimuli when these alternate with reward predicting visual stimuli Figure  left 2727,29,32 Pseudoconditioning may arise when a primary reinforcer sets a contextual background and provokes unspecific behavioral responses to any events within this context . As dopaAlthough stimuli with substantial physical salience seem to drive dopamine neurons ,58-60 (sTaken together, many of the non-reward coding dopamine activations may be due to stimulus generalization or, in particular, pseudoconditioning. Nevertheless, there seem to remain true activations to unrewarded control stimuli and to primary and conditioned aversive stimuli in a limited proportion of dopamine neurons when these factors are ruled out. Further experiments assessing such responses should use better controls and completely eliminate all contextual reward associations with stimuli in the laboratory.Given the occurrence of non-reward coding activations, it is reasonable to ask how an animal would distinguish rewarding from unrewarded stimuli based on a dopamine response. The very rapid, initial, pseudoconditioned and poorly discriminative response component might provide a temporal bonus for faciliating fast, default behavioural reactions that help the animal to very quickly detect a potential reward . By contIf a reward signal reflects the mean reward prediction error scaled by the standard deviation of reward probability distributions, and if we view standard deviation as a measure of risk, could there be a direct neuronal signal for risk? When reward probabilities vary from 0 to 1 and the reward magnitude remains constant, the mean reward value increases monotonically with probability, whereas the amount of risk follows an inverted U function peaking at p = 0.5 Figure , inset. About one third of dopamine neurons show a relatively slow, moderate, statistically significant activation that increases gradually during the interval between the reward predicting stimulus and the reward; this response varies monotonically with risk Figure  18]. Th. Th18]. Due to its lower magnitude, the risk signal is likely to induce lower dopamine release at dopamine varicosities compared to the more phasic activations coding reward value. The relatively low dopamine concentration possibly induced by the risk signal might activate the D2 receptors which are mostly in a high affinity state but not the low affinity D1 receptors . By contA dopamine risk signal may have several functions. First, it could influence the scaling of the immediately following prediction error response by standard deviation immediately after the reward . Second,The author declares that he has no competing interests.WS wrote the paper.


Environmental Health Perspectives (EHP) will note several changes in the masthead of the journal, reflecting a renewed commitment to publishing the best research and news in the environmental health sciences. In the 4 months since I assumed the role of editor-in-chief for EHP, I have added 21 new associate editors and 26 new Editorial Review Board members. Associate editors are responsible for managing the peer review of papers and making a recommendation to the journal concerning the acceptability of a manuscript to be published in EHP. The Editorial Review Board serves as a pool of potential reviewers for manuscripts submitted to the journal.Readers of EHP editors emeritus (James Burkhart and Thomas Goehl).I have also established an Advisory Board to provide feedback and recommendations concerning performance and emerging issues facing the journal. This board is made up of 2 NIEHS scientists (Kenneth Korach and Steven Kleeberger), 3 scientists external to the NIEHS , and 2 EHP has been very fortunate to have these dedicated and committed scientists involved in the editorial process over the last year. Today, I head an internal working group that screens all incoming papers. Those papers passing the screening phase are assigned to one of the associate editors for processing.After the December 2006 retirement of former acting editor-in-chief James Burkhart, research submissions were screened by a group of interim editors to determine if the manuscript was consistent with the quality, scope, and mission of the journal. This group was led by Kenneth Korach and included NIEHS scientists Matthew Longnecker, Stephanie London, and Michael Waalkes, along with Steven Kleeberger and James Burkhart. In addition to screening papers for subsequent review, this group was responsible for handling the peer review of the remaining papers. EHP was approximately 10 months. However, EHP publishes all papers online within 24 hours of acceptance, which averages about 6.5 months from the date of submission.In 2007, approximately 40% of the 1,108 papers received were deemed worthy of review; the rest were returned to authors without further review. Moreover, the journal averaged approximately 190 pages per issue in 2007, publishing 276 peer-reviewed research articles, 13 full-length reviews, 7 commentaries, and 9 reports of workshops and meetings. The overall acceptance rate for all peer-reviewed papers in 2007 was 19%, down from 29% the previous year. An evaluation of the submission data for 2007 revealed that the average time to first decision for peer-reviewed journals in general was approximately 2 months, whereas the average time from submission to publication in EHP ’s international partnership journals Mali Médical, Ciencia y Trabajo, Ciência de Saúde Coletiva, and the Journal of Environmental and Occupational Medicine. As a component of its international program, EHP hosts an online version of the quarterly Mali Médical, a French-language journal published by the Société de Médecine du Mali. Selected news articles from EHP are translated into Spanish for the quarterly Ciencia y Trabajo, published by the Fundación Científica y Tecnológica, Asociación Chilena de Seguridad. Abstracts of selected review articles are translated into Portuguese for the quarterly Ciência de Saúde Coletiva, published by the Associação Brasileira de Pós-Graduação em Saúde Coletiva. In collaboration with the Shanghai Municipal Center for Disease Control and Prevention (SCDC), more than 30,000 copies of the EHP Chinese Edition are distributed in China on a quarterly basis. The SCDC also publishes the Journal of Environmental and Occupational Medicine.The masthead also now lists the editors of EHP staff identify topics and themes for articles in the Environews section of the journal. Members of the News Committee represent a cross-section of NIEHS scientific and policy leaders knowledgeable about emerging themes and topics in the environmental health sciences. Once a topic is chosen for coverage in the Environews section, EHP news staff contact professional science writers to write articles, which undergo subject matter expert review and internal editing. Environews consists of several sections, including the Forum (short reports on current topics of interest); Focus articles ; Spheres of Influence articles ; Innovations articles ; and Science Selections articles . Environews constitutes approximately 10% of each issue.Readers will note the presence of the News Committee on the masthead. Formerly identified as “Contributing Editors,” this group helps EHP in 2008 is promising. We plan to implement a new web-based manuscript tracking system by late spring of this year. This new system will make it easier to submit and review research papers, and it will allow us to make more effective use of our talented Board of Associate Editors in handling manuscripts. We also have plans to enhance our website and build on existing international partnerships to reach a wider audience outside the United States. Finally, we have received funding to reinstate the EHP Student Edition, a free online resource that provides lessons based on EHP news articles to high school science teachers. These lessons align with National Science Education Standards in biology, chemistry, environmental science, geology, and physical science. The first new lessons will debut in September 2008. In the meantime, we are conducting a survey to help us direct our efforts to best meet the needs of EHP Student Edition users. If you would like to complete the survey, please visit the EHP Science Education website (http://www.ehponline.org/science-ed-new/).The overall picture for


The design and control of molecular self-assembly is of great interest in the development of new molecular architectures with multiple desired functions or properties. In this context, the gelling systems formed by low molecular weight gelators are particularly promising and are the subject of an ever increasing number of studies.4 molecules of solvent per molecule of gelator in the gel composition), thus creating extraordinary variations of the physical properties of the system. These physical gels are usually thermoreversible (reversible sol-gel transition by heating and cooling) and, depending on the molecular structure of the gelling agent and the fluid which is rigidified, it is possible to form nanoscale superstructures such as nanofibres, nanoribbons, nanosheets, nanoparticles, helical windings, etc., which are of interest for materials and nanoobject conception.A gel consists of one or more gelling agents and a fluid  which behaves as a visco-elastic material (soft matter) due to the immobilization of solvent molecules in a three-dimensional network. This network results from the self-assembly of the gelling agent into fibres via non-covalent interactions such as hydrogen bonding, π–π stacking, van der Waals and electrostatic interactions, coordination, and charge transfer. Additional non-covalent interactions lead to physical entanglement of the fibres, which creates a 3D network, the fluid being trapped in the nanoscale interstices. A very large quantity of solvent can be imprisoned in the supramolecular network (in the case of supergelators it is not rare to observe more than 10Thus, owing to their non-conventional behaviour, low molecular weight gelators are very attractive for applications in various areas, including supramolecular templates or matrices, transport and release of drugs, art conservation, cosmetics, sensors, optoelectronics, actuators, etc. However, despite numerous efforts to establish a structure-property relationship for the development of low molecular weight gelling agents, prediction of the gelling ability of a compound is not straightforward. A major challenge today is the rational design of small size molecular gelators coupled with an understanding of the mechanism of gelation. It is also important to develop future green gelators for eco-compatible applications.This thematic series on organogels and hydrogels will address these various points with a particular emphasis on the molecular requirements on the gelling ability, the different approaches for producing molecular gelators, and some techniques used for the characterization and the properties of the gels.It is my great pleasure to act as guest editor of this Thematic Series, which gathers a wide range of expertise to meet the demands of this interdisciplinary field. I warmly thank all the authors who have enthusiastically accepted to contribute to this series which will give the reader a clear overview of this rapidly developing research field and will identify future growth areas.Jean-Pierre DesvergneTalence, July 2010


EHP , Marina Camatini and Ezio Bolzacchini  were listed as authors. However, they have notified EHP that they were not informed about the letter and that their names were included without their permission. Both Bolzacchini and Camatini have requested to have their names removed; therefore, EHP will honor their request and remove their names from the online versions of the letter.In the letter “Traffic-Related Air Pollution and Childhood Asthma,” published in the July issue of


Methylphenidate is a psychostimulant that inhibits the neuronal dopamine transporter. In addition, methylphenidate has the intriguing ability to provide neuroprotection from the neurotoxic effects of methamphetamine and perhaps also Parkinson’s disease; both of which may likely involve the abnormal accumulation of cytoplasmic dopamine inside dopaminergic neurons and the resulting formation of dopamine-associated reactive oxygen species. As delineated in this review, the neuroprotective effects of methylphenidate are due, at least in part, to its ability to attenuate or prevent this abnormal cytoplasmic dopamine accumulation through several possible neuropharmacological mechanisms. These may include 1) direct interactions between methylphenidate and the neuronal dopamine transporter which may attenuate or prevent the entry of methamphetamine into dopaminergic neurons and may also decrease the synthesis of cytoplasmic dopamine through a D2 receptor-mediated signal cascade process, and 2) indirect effects upon the functioning of the vesicular monoamine transporter-2 which may increase vesicular dopamine sequestration through both vesicle trafficking and the kinetic upregulation of the vesicular monoamine transporter-2 protein. Understanding these neuropharmacological mechanisms of methylphenidate neuroprotection may provide important insights into the physiologic regulation of dopaminergic systems as well as the pathophysiology of a variety of disorders involving abnormal dopamine disposition ranging from substance abuse to neurodegenerative diseases such as Parkinson’s disease. It was first synthesized in 1944 dihydrotetrabenazine (DHTBZ), and vesicular DA content in a rat model of METH neurotoxicity DHTBZ, in cytoplasmic vesicles purified from mice striata [3H]DHTBZ binding in whole striatal homogenates prepared from treated mice. These and other vesicle trafficking data suggest that multiple high-dose METH administrations cause a subcellular redistribution of VMAT-2 containing vesicle out of the cytoplasm such that fewer VMAT-2, and presumably associated cytoplasmic vesicles, are available to sequester DA DHTBZ is affected similarly [max of DA transport and the density of kinetically active VMAT-2 without changing the Km, the catalytic rate constant, or the rate constant for DA binding to the VMAT-2 [This possible mechanism of neuroprotection is supported by the experimental findings that MPD increases and decreases VMAT-2 immunoreactivity in the cytoplasmic and membrane-associated vesicle subcellular fractions, respectively, without altering total synaptosomal VMAT-2 content . Bindingimilarly . The traimilarly , 47, 65.e VMAT-2 . MPD alse VMAT-2 , 65 whice VMAT-2 . This sue VMAT-2 , 62. In the second possible neuropharmacological mechanism of neuroprotection, MPD actually alters the functioning of VMAT-2 in the membrane-associated vesicles to transport more DA. This mechanism is supported by the findings that, in addition to redistributing vesicles away from membranes and into the cytoplasm, MPD also increases vesicular DA sequestration into the remaining membrane-associated vesicles . MPD thuThese MPD-induced increases in vesicular DA sequestration may have several additional interesting functional consequences. The increase in vesicular DA transport increases vesicular DA content with no change in whole striatal tissue DA content , 65. By 3), attenuate or prevent the abnormal accumulation of cytoplasmic DA and the resulting formation of potentially neurotoxic DA-associated reactive species. At present, it is difficult to quantify the amount that any individual mechanism contributes to MPD neuroprotection in vivo. Further studies investigating the neuropharmacology, biochemistry, and molecular biology underlying these mechanisms are warranted as these will help to determine the in vivo contribution of each mechanism. These additional studies may also provide insight into the physiologic regulation of dopaminergic systems as well as the pathophysiology of a variety disorders involving abnormal DA disposition ranging from substance abuse to neurodegenerative diseases such as Parkinson’s disease. Ultimately, this may suggest leads for developing related novel and more effective neuropharmacologic therapeutic treatment strategies.The studies reviewed above help us to understand how MPD has the ability to provide neuroprotection against METH-induced neurotoxicity and perhaps Parkinson’s disease through possible mechanisms involving direct interactions with the DAT and additional mechanisms involving indirect effects upon the VMAT-2. These mechanisms, summarized in Fig. (