The echolocating bat controls not only the spectral–temporal features of its echolocation cries but also the aim and directional characteristics of its sonar beam. Eptesicus fuscus is an oral emitter, and the sonar beam is aligned with the head. A linear microphone array was used to record the big brown bat’s sonar signals at 16 different locations in the flight room. For each video frame in which a vocalization was detected, the normalized beam intensity at each microphone was computed. E. fuscus emits a broad band FM call with a first harmonic sweeping down from ca . 60 to 25 kHz. The original signal was decomposed into three sub-bands (20–30 kHz, 30–40 kHz, 40–50 kHz) and the intensities computed in each sub- band for every vocalization. Using standard tables (ISO 9613-1) a scaling factor correcting for the sound absorption due to air was computed for each frequency band (see Lawrence and Simmons, 1982). Finally, the intensities in each band were corrected for spherical loss and summed to yield a normalized intensity for each vocalization in the direction of each microphone. Vectors were drawn from the bat to each microphone. The length of each vector was made proportional to the normalized intensity at the corresponding microphone. Based on these vectors we constructed a normalized shading pattern such that the peak intensity has a value of 1.0 and is colored black. Lighter colors denote progressively lower
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Certain tiger moths emit high-frequency clicks to an attacking bat, causing it to break off its pursuit. The sounds may either orient the bat by providing it with information that it uses to make an attack decision (aposematism) or they may disorient the bat by interrupting the normal flow of echo information required to complete a successful capture (startle, jamming). At what point during a bat’s attack does an arctiid emit its clicks? If the sounds are aposematic, the moth should emit them early in the attack echolocation sequence in order to allow the bat time to understand their meaning. If, however, the sounds disrupt the bat’s echo-processing behaviour, one would expect them to be emitted later in the attack to maximize their confusion effects. To test this, we exposed dogbane tiger moths (Cycnia tenera) to a recording of the echolocation sequence emitted by a big brown bat (Eptesicus fuscus) as it attacked a stationary target. Our results demonstrate that, at normal echolocation intensities, C. tenera does not respond to approach calls but waits until the terminal phase of the attack before emitting its clicks. This timing is evident whether the moth is stationary or flying and is largely independent of the intensity of the echolocation calls. These results support the hypothesis of a jamming effect (e.g. ‘phantom echoes’) and suggest that, to determine experimentally the effects of arctiid clicks on bats, it is important that the bats be tested under conditions that simulate the natural context in which this defence operates.
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Four big brown bats (Eptesicus fuscus) were challenged in an obstacle avoidance experiment to localize vertically stretched wires requiring progressively greater accuracy by diminishing the wire-to- wire distance from 50 to 10 cm. The performance of the bats decreased with decreasing gap size. The avoidance task became very difficult below a wire separation of 30 cm, which corresponds to the average wingspan of E. fuscus. Two of the bats were able to pass without collisions down to a gap size of 10 cm in some of the flights. The other two bats only managed to master gap sizes down to 20 and 30 cm, respectively. They also performed distinctly worse at all other gap sizes. With increasing difficulty of the task, the bats changed their flight and echolocation behaviour. Especially at gap sizes of 30 cm and below, flight paths increased in height and flight speed was reduced. In addition, the bats emitted approach signals that were arranged in groups. At all gap sizes, the largest numbers of pulses per group were observed in the last group before passing the obstacle. The more difficult the obstacle avoidance task, the more pulses there were in the groups and the shorter the within-group pulse intervals. In comparable situations, the better-performing bats always emitted groups with more pulses than the less well-performing individuals. We hypothesize that the accuracy of target localization increases with the number of pulses per group and that each group is processed as a package.
Previous research has demonstrated that the big brown bat uses a constant absolute target direction (CATD) flight strategy, which is nearly time optimal, to intercept its insect prey (Ghose et al., 2006). However, it is still an open question as to whether the big brown bat applies the same strategy when interacting with conspecifics. Two flight control strategies, classical pursuit (CP) and CATD, are examined here as possible strategies the bat may use to interact with another bat. The CP strategy refers to a configuration in which one animal always points its velocity vector towards the position of a target animal (Klamkin and Newman, 1971; Wei et al., 2009). When bats exhibit CATD, the lines jointing the two animals’ flight trajectories are parallel at any time, and hence the angle between the conspecific and a fixed reference is constant (Justh and Krishnaprasad, 2006). Based on the prior work, we are led to predict that paired big brown bats employ the same CATD strategy when they fly together as the strategy they use to pursue insect prey.
Two of the most common species of bats in the continental Unites States are the big brown bat (Eptesicus fuscus) and the little brown bat (Myotis lucifugus) (5). These highly colonial species are adapted to living in both urban and rural areas. On the basis of data from public health rabies laboratories, big brown bats and little brown bats are the bat species most commonly submitted for rabies testing. The large number of submissions stems from hu- man or domestic animal exposure (6). Despite frequent interac- tion, only three human rabies cases acquired in the United States have been associated with the little brown bat or big brown bat RABV since 1990 (Fox News). The RABV most often associated with human rabies cases acquired in the United States is the silver-haired bat (La- sionycteris noctivagans) RABV (LnRV) (7; http://www.cdc.gov/rabies /location/usa/surveillance/humanrabies.html). Unlike big brown or little brown bats, silver-haired bats are tree-dwelling bats that form small colonies, and thus, human interaction with this species is infrequent (7). Previous studies have postulated that the silver- haired bat RABV possesses an increased pathogenicity, including the ability to replicate at lower temperatures and infect nonneu- ronal cell lines (8, 9). These unique characteristics increase the transmissibility of LnRV, posing a greater exposure risk to more gregarious bat or domestic animal species, thereby increasing the possibility of human-LnRV interaction.
The jamming stimulus was a continuous CF tone that was turned on and remained on for all 10 jamming trials. Presenting tone-bursts instead of a continuous tone introduces spectral ‘splatter’ at the onset and offset of each burst, and this widens the spectrum enough that it might disrupt the sharpness of the jamming frequency to the bat. Without knowing how specific any potential jamming effect might be to each frequency, it is better to keep the interfering stimulus restricted to one frequency at a time. For each session a different fixed frequency in the frequency range from 18 to 32·kHz was used as the CF jamming stimulus. Each bat completed one session (day) of testing for each jamming condition with the CF jamming stimulus at 18, 20, 22, 23, 24, 25, 26, 27, 28, 29, 30 and 32·kHz. These sessions were presented in a pseudorandom order on separate days. The CF jamming sounds were generated by a Model 27A Audio Generator (Leader, Inc., Yokohama, Japan), and delivered from an electrostatic loudspeaker Model EST-2 (LTV, Corp., Los Angeles, CA, USA) after being amplified by a Model 7500 power amplifier (Krohn-Hite, Inc., Avon, MA). As shown in Fig.·2, the loudspeaker was located 1.5·m from the bat and was oriented to produce a uniform sound field around the bat’s location on the Y-shaped platform. The frequency of the jamming sound was adjusted by the recorder using a Model LDC-831 Frequency Counter (Leader, Inc., Japan). Fig.·3 shows the frequencies and sound pressures of the CF jamming stimuli in relation to the hearing sensitivity (audiogram) of the big brown bat (Dalland, 1965; Koay et al., 1997). Sound pressures were measured at the center of the Y-platform, at the starting point for the bats. The hearing sensitivity of the bats varies by only a few decibels around 10·dB SPL at frequencies from 18 to 32·kHz, and the jamming sounds were adjusted in amplitude to be at a fixed sensation level of 65·dB for all these frequencies. This level is approximately that of the echoes that the bat was receiving from the experimental target. The bats’ own emissions were much more intense (100–110·dB SPL) and were clearly discernable from the jamming stimulus on waveforms and spectrograms of the trials.
In this study, only occasionally did vocalizations of paired bats overlap in time. Instead, there were temporal gaps between the calls of individual bats, and the intervals between calls varied over the course of each trial. Two bird species, the red-eyed vireo (Vireo olivaceus) and the least flycatcher (Empidonax minimus), modify temporal patterns of their songs to avoid signal overlap (Ficken et al., 1974). Male singing nightingales (Luscinia megarhynchos) sing preferentially during the silent windows between heterospecific songs in order to transmit their songs more efficiently (Brumn, 2006). The cotton-top tamarins (Saguinus oedipus) can adjust their vocalizing time to fall into the silent windows between white noises (Egnor et al., 2007). The tropical frog, Eleutherodactylus coqui, also adjusts the timing of its mating calls to fall in gaps between the vocalizations of neighboring frogs (Narins, 1992; Zelick and Narins, 1983). The echolocating bat could apply the same principle by listening to the other bat’s vocalizations to select its call timing, and when intervals between the calls of paired bats are short enough to create interference, this may drive further adjustments to sonar signal design. Support for this comes from our present finding that the largest call design separations occurred when one bat vocalized less than 5 ms after the other bat’s vocalizations. The increases in call design differences for closely timed calls imply that the big brown bat actively controls timing and call features to avoid call interference from conspecifics. As elaborated below, behavioral studies of echo ranging by echolocation in bats have reported that interfering signals disrupt distance discrimination, and the acoustic feature and temporal separation between jamming signals and echoes affects the magnitude of interference (Masters and Raver 1996; Møhl and Surlykke 1989; Roverud, 1989; Roverud and Grinnell, 1985a; Roverud and Grinnell, 1985b).
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The big brown bat, Eptesicus fuscus, uses echolocation for orientation and foraging, and scans its surroundings by aiming its sonar beam at obstacles and prey. All call parameters are highly adaptable and determine the bat ’ s acoustic field of view and hence its perception of the echo scene. The intensity (source level) and directionality of the emitted calls directly contribute to the bat ’ s acoustic field of view; however, the source level and directionality of the big brown bat ’ s sonar signals have not been measured in the field. In addition, for bats, navigation and prey capture require that they process several streams of acoustic information. By using stereotypic flight paths in known areas, bats may be able to reduce the sensory processing load for orientation and therefore allocate echo processing resources to prey. Here we recorded the echolocation calls from foraging E. fuscus in the field with a microphone array and estimated call intensity and directionality, based on reconstructed flight trajectories. The source levels were intense with an average maximum source level of 138 dB (root mean square re. 20 µPa at 0.1 m). Furthermore, measurements taken from a subset of calls indicate that the echolocation signals in the field may be more directional than estimated in the laboratory (half- amplitude angle 30 deg at 35 kHz). We also observed that E. fuscus appear to follow stereotypic flight paths, and propose that this could be a strategy to optimize foraging efficiency by minimizing the sensory processing load.
The moths used in our exposure trials were significantly less sensitive to the calls of gleaning M. septentrionalis than to the aerial calls of M. lucifugus. In addition, M. septentrionalis often ceased echolocating prior to attacking, presumably relying on passive auditory cues (moth fluttering sounds) for prey detection, thereby denying moths the acoustic cues necessary for predator detection. The calls of M. septentrionalis rarely elicited more than three auditory spikes per sound pulse, similar to levels of firing reported for congeneric moths exposed to hunting bats (probably Myotis and Eptesicus spp.) 30–40m away (Roeder, 1962). The moths in our flight cage were never more than 2 m from a bat, and most of the action potentials elicited in response to calling M. septentrionalis were from bats that were hovering less than 50cm away or attacking. Even when the ear was fully exposed, the average A1 receptor firing rate was approximately 1 spike per echolocation pulse. These spike rates are no greater than spontaneous firing levels for A1, and should be rejected as background noise by interneurones within the moth’s CNS (e.g. Boyan and Fullard, 1988).
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Glucocorticoids (GCs) are potent regulators of energy metabolism. Chronic GC exposure suppresses brown adipose tissue (BAT) thermogenic capacity in mice, with evidence for a similar effect in humans. Intracellular GC levels are regulated by 11 b -hydroxysteroid dehydrogenase type 1 (11 b -HSD1) activity, which can amplify circulating GC concentrations. Therefore, 11 b -HSD1 could modulate the impact of GCs on BAT function. This study investigated how 11 b -HSD1 regulates the molecular architecture of BAT in the context of GC excess and aging. Circulating GC excess was induced in 11 b -HSD1 knockout (KO) and wild-type mice by supplementing drinking water with 100 m g/mL corticosterone, and the effects on molecular markers of BAT function and mitochondrial activity were assessed. Brown adipocyte primary cultures were used to examine cell autonomous consequences of 11 b -HSD1 de- ficiency. Molecular markers of BAT function were also examined in aged 11 b -HSD1 KO mice to model lifetime GC exposure. BAT 11 b -HSD1 expression and activity were elevated in response to GC excess and with aging. 11 b -HSD1 KO BAT resisted the suppression of uncoupling protein 1 (UCP1) and mitochondrial respiratory chain subunit proteins normally imposed by GC excess. Furthermore, brown adipocytes from 11 b -HSD1 KO mice had elevated basal mitochondrial function and were able to resist GC-mediated repression of activity. BAT from aged 11 b -HSD1 KO mice showed elevated UCP1 protein and mitochondrial content, and a favorable profile of BAT function. These data reveal a novel mechanism in which increased 11 b -HSD1 expression, in the context of GC excess and aging, impairs the molecular and metabolic function of BAT. (Endocrinology 158: 1964 – 1976, 2017)
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BAT, in human fetuses and newborns, is found in axillary, cervical, perirenal, and periadrenal regions, but decreases shortly after birth and has traditionally been considered insignificant in adults [47, 53, 54]. Brown adipocytes are smaller than white adipocytes, their cyto- plasm contains several lipid droplets, a roundish nucleus and numerous, large, generally spherical mitochondria with laminar cristae . The multilocality of BAT max- imizes the cytoplasmic-lipid interface, making large amounts of fatty acids available quickly for mitochon- drial uncoupling and consequent thermogenesis . BAT is an important player in energy expenditure be- cause of its ability to convert energy toward heat using uncoupling protein 1 (UCP1), a process called non- shivering thermogenesis . The high metabolic activ- ity of BAT and adipose tissue browning, referring to the formation of so-called beige adipocytes in WAT [56, 57], suggest that the activation of brown and beige adipo- cytes may be successfully targeted to combat metabolic and cardiovascular diseases in humans.
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Abstract: Human rabies is almost invariably fatal, and globally it remains an important public health problem. Our knowledge of rabies pathogenesis has been learned mainly from studies performed in experimental animal models, and a number of unresolved issues remain. In contrast with the neural pathway of spread, there is still no credible evidence that hematogenous spread of rabies virus to the central nervous system plays a significant role in rabies pathogenesis. Although neuronal dysfunction has been thought to explain the neurological disease in rabies, recent evidence indicates that structural changes involving neuronal processes may explain the severe clinical disease and fatal outcome. Endemic dog rabies results in an ongoing risk to humans in many resource-limited and resource-poor countries, whereas rabies in wildlife is important in North America and Europe. In human cases in North America, transmission from bats is most common, but there is usually no history of a bat bite and there may be no history of contact with bats. Physicians may not recognize typical features of rabies in North America and Europe. Laboratory diagnostic evaluation for rabies includes rabies serology plus skin biopsy, cerebrospinal fluid, and saliva specimens for rabies virus antigen and/or RNA detection. Methods of postexposure rabies prophylaxis, including wound cleansing and administration of rabies vaccine and human rabies immune globulin, are highly effective after recognized exposure. Although there have been rare survivors of human rabies, no effective therapy is presently available. Therapeutic coma (midazolam and phenobarbital), ketamine, and antiviral therapies (known as the “Milwaukee protocol”) were given to a rabies survivor, but this therapy was likely not directly responsible for the favorable outcome. New therapeutic approaches for human rabies need to be developed. A better understanding of basic mechanisms involved in rabies pathogenesis may be helpful in the development of potential new therapies for the future.
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Fig. 4. Model highlighting differentially expressed genes involved in fuel utilization and heat generation in brown adipose tissue (BAT) during hibernation. The role of gene products in various metabolic processes in a brown adipocyte is shown. Genes with abbreviations in red meet the criteria for differential expression, showing highest messenger ribonucleic acid (mRNA) levels during the hibernation phases of torpor or interbout arousal (IBA). Abbreviations of genes that are not differentially expressed but their mRNAs are highly abundant and/or encoded by tissue-specific genes in BAT, are shown in black. Molecules that serve as a source of fuel are labeled in green. Data were taken from a transcriptomic study using RNA sequencing (Hampton et al., 2013). Ad, adenosine; ADP, adenosine diphosphate; AMP, adenosine monophosphate; ATP, adenosine triphosphate; cAMP, cyclic adenosine monophosphate; NA, noradrenaline; NEFA, non-esterified fatty acid; TAG, triacylglycerol; UCP1, uncoupling protein 1. Figure is duplicated from Hampton et al., 2013 (with
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It is now widely accepted that in addition to func- tioning as a daily buffer for circulating lipids, adipose tissue also plays a key role in the regulation of energy balance and glucose homeostasis via release of circulating metabolites and hormonal factors (11). Indeed, secreted adipokines have been investigated intensively for their roles in energy homeostasis (12) in an attempt to iden- tify novel pathways for the treatment of obesity and its associated comorbidities. The endocrine FGFs have emerged as a novel family of hormonal factors that, when administered to rodents, have substantial antidiabetic activity (13). The downstream capabilities of FGF ligands are highly dependent upon engagement of FGFR1c, the predominant FGFR expressed in WAT and BAT (4). Indeed, mice with adipose-selective FGFR1 knockout were refractory to FGF21-induced improvements in glucose metabolism and body weight (8).
Although leptin is involved in regulating energy balance, the relationship between leptin and energy expenditure is still ambiguous. Leptin administration to mice or rats increased oxygen consumption, UCP1 mRNA and protein expression (Hwa et al., 1997; Scarpace and Metheny, 1998; Xiao et al., 2004). However, BAT thermogenesis was reduced in cold- acclimated rats when they were injected with exogenous leptin (Abelenda et al., 2003). Leptin administration to post- hibernatory Arctic ground squirrels did not alter RMR, BAT UCP1 mRNA and protein levels, but reduced food intake and weight gain (Boyer et al., 1997). The present study showed that serum leptin levels were negatively correlated with RMR (corrected for body mass) during lactation and cold exposure, in contrast to the proposed relationship between leptin and energy expenditure (Hwa et al., 1997). In previous studies on the cold-acclimated or seasonally acclimatized Brandt’s voles (Li and Wang, 2005b; Zhang and Wang, 2006), the decreased serum leptin levels were also associated with increased RMR and thermogenesis. Moreover, we found that serum leptin levels (corrected for body mass) were positively correlated with UCP1 content only in the warm-acclimated voles, but not in the cold. These data suggest that in warm-acclimated voles, leptin may be involved in decreasing energy expenditure by inducing the thermogenesis, while in the cold, the increase in thermogenesis activated by the sympathetic nerve may conceal the reduction of thermogenesis by decreased serum leptin. Although the exact relationship between leptin and energy expenditure could not be determined just by the correlation analysis, the recent finding that a leptin antagonist blocked leptin-mediated anorexic effects as well as the increase in BAT UCP1 protein (Zhang et al., 2006), confirms that leptin plays roles in regulating not only food intake but also thermogenesis. Brandt’s voles can suppress thermogenesis during lactation. The conserved available energy might be used for milk production and/or to avoid overheating during lactation (Johnson et al., 2001a; Król and Speakman, 2003). During simultaneous cold exposure and lactation, however, the voles can increase thermogenesis. Serum leptin, secreted according to the body status and circumstances, was negatively related to the energy intake and RMR. These data suggest that Brandt’s voles can adjust energy intake and thermogenesis to accommodate simultaneous lactation and cold exposure, and serum leptin may potentially be involved in the regulation of energy intake and thermogenesis, but the thermoregulation in the cold may be mainly mediated by other factors.
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AEDs: Antiepileptic drugs; AN-BP: Anorexia nervosa-binge purge subtype; AN-R: Anorexia nervosa-restricting subtype; ARFID: Avoidant/restrictive food intake disorder; BAT: Brown adipose tissue; BMD: Bone mineral density; BMI: Body mass index; BN: Bulimia nervosa; D2: Ergocalciferol; D3: Cholecalciferol; DSM – V: Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition; DSM-IV: Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition; DXA: Dual-energy X-ray absorptiometry; ED-NOS: Eating disorder not otherwise specified; FDA: US Food and Drug Administration; FRAX: Fracture risk assessment tool; GH: Growth hormone; IGF-1: Insulin-like growth factor-1; IOF: International Osteoporosis Foundation; ISCD: International Society of Clinical Densitometry; NOF: National Osteoporosis Foundation; OCP: Oral contraceptive pills; PPIs: Proton-pump inhibitors; PTH: Parathyroid hormone; RANKL: Receptor activator of nuclear factor kappa-B ligand; SIR: Standardized incidence ratio; SSRIs: Selective serotonin reuptake inhibitors; WHO: World Health Organization
It is well known that obesity comes with expansion of WATs, which generally contains two distinct processes, one in the form of hyper- trophy (characterized by an enlargement in adipocyte size) and the other in the form of hyperplasia (characterized by new adipocyte generation from progenitor and preadipocyte cells) (13, 15, 28). We found that iWAT weight reduced significantly in ABKO mice, while the weights of eWAT and BAT were unaltered (Fig. 5, A to C). Thereafter, the adipocyte size of iWAT was carefully examined but appeared to be highly similar between ABKO and control mice (Fig. 5, D to F). Meanwhile, the expression of genes related to fatty acid synthesis and lipolysis was further examined and also showed no significant alterations either in iWAT, eWAT, or BAT between the two groups (fig. S6, A to F). The expression of adipogenesis- related genes was not different in adipose tissues either (fig. S6, G to I). These results strongly suggested that -catenin regulated iWAT mass not through affecting hypertrophy. It is previously reported that iWAT expansion involves hyperplasia due to the notable in- crease in adipocyte progenitor proliferation in response to HFD (28). We hypothesized that the reduced iWAT mass in ABKO mice might result from decreased progenitor or preadipocyte proliferation and the consequent lower hyperplasia for newborn adipocytes. As shown in Fig. 5G, Pdgfr + preadipocytes, which reside in SVFs and con- tribute to new white adipocyte generation in response to HFD (8), were significantly decreased in ABKO mice (Fig. 5G). The percentage of proliferated preadipocytes, marked by BrdU + Pdgfr + double labeling, was also decreased in ABKO mice (Fig. 5H), indicating that the blunted proliferation of preadipocytes was associated with the restricted mass expansion in iWAT of ABKO mice. Consistently, the progenitors marked by other recently identified markers, such as Cd142 and Icam1, were also significantly reduced in the iWAT of ABKO mice (fig. S6, J to Q) (10). There were no obvious changes in these progenitors in eWAT of ABKO mice (fig. S6, J to Q). These data together may suggest that ablation of -catenin in mature adipocytes reduced hyperplastic adipose expansion through reducing the proliferation of preadipocytes.
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Methods: Nine-month-old male breeders Wistar rats of two groups were studied: 8 rats submitted to IIH and 5 control rats submitted to sham IIH. The rats were weighed at the baseline and at the end of three weeks, after being placed in the IIH apparatus seven days per week, eight hours a day, in the lights on period, simulating an apnea index of 30/hour. After experimental period, the animals were weighed and measured as well as the BAT, abdominal, perirenal, and epididymal fat, the heart, and the gastrocnemius muscle.
Immune cells reside in adipose tissue and interactions involving these cell types play a significant role in modulating systemic metabolism and inflammatory status [42, 53, 54]. Genes with decreased expression in BAT were disproportionately associated with immunity and inflammation response (Supplemental Figure 2), suggesting attenuated BAT immune cell infiltration in GHRKO mice. Given the close associations between inflammation and mitochondrial dysfunction , we used data from the Immunological Genome Project  to computationally discern the identity of immune cell types contributing to this pattern [56-58]. This showed that genes with decreased expression in GHRKO BAT were often expressed by DC and macrophage populations. Both of these monocyte-derived cell types are commonly associated with adipose tissue and tend to become more numerous in adipose as a result of obesity . This inflammatory process has been best characterized in WAT (rather than BAT), although prior studies have identified increased BAT macrophage numbers in obese mouse genotypes . DCs are also commonly associated with adipose tissue, particularly in the obese state, and their presence appears to facilitate development of Th17 responses and obesity-associated insulin resistance [61, 62]. In GHRKO mice, reduced BAT infiltration by macrophages and/or DCs may dampen systemic inflammation with aging and contribute to insulin sensitivity. These immune cell types, moreover, are reported to have deleterious effects on adipose metabolism . Their reduced prominence in GHRKO BAT could contribute to the apparent enhancement of BAT mitochondrial activity discussed above. Interestingly, the same analysis in WAT revealed that immune cell populations were affected to a far lesser extent by Ghr ablation (Figure 6). In fact, in WAT we detected increased expression of genes expressed by non-immune cell types, particularly cells of stromal and fibroblastic origin. This may reflect a pro-proliferative and stem cell-like phenotype of GHRKO WAT, which may account for the greater progenitor differentiation capacity previously
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The chromosomal regions containing QTL identified in this study are relatively large and contain many known and unknown genes. Although the specific genes re- sponsible for these QTL effects cannot yet be identified, the presence of intriguing candidate genes within these QTL regions deserves mention. Genes encoding the b-subunit of thyroid stimulating hormone (Tshb) and the neuropeptide Y receptor Y2 (Npy2r) are located in the region of chromosome 3 containing Hlq4 and Batq2 (Naylor et al. 1986; Nakamura et al. 1996). Both of these genes are involved in the regulation of several metabolic processes and have been implicated in the specific regulation of brown adipose activity (Himms- Hagen 1989; Cassard-Doulcier et al. 1994; see Woods et al. 1998). Genes encoding uncoupling proteins 2 and 3 are located on chromosome 7 within the region con- taining Hlq5 (Boss et al. 1997; Fleury et al. 1997; Vidal- Puig et al. 1997). Uncoupling proteins facilitate the dissipation of energy as heat and have been actively investigated as candidate genes for obesity-related phe- notypes (Bouchard et al. 1997).
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