stroke is the third cause of mortality and the first 
 cause of disability in adults [ 1 , 2 ] . as cerebral ischemia can not be predicted , timely 
 imaging and accurate interpretation are required to identify patients who might 
 benefit from more aggressive therapy . although computed tomography ( ct ) and 
 magnetic resonance imaging ( mri ) have been important and widely used clinical 
 imaging techniques , there are some shortcomings in the imaging of acute stroke , 
 such as the limited brain coverage . however , up to now , the markers of 
 cerebral ischemia were scarce [ 2 , 3 ] . the ideal cerebral ischemia markers should not only per - meate 
 across the bbb but also accumulate in the brain ischemia . recently , mathis et al . synthesized a series of thio - flavin - t 
 derivatives , which had the  benzothiazole - aniline  backbone and showed good 
 permeation across the bbb [ 46 ] . also it is well known that 
 the nitroimidazole derivatives can selectively accumulate in hypoxic tissue and 
 be used to image tumor hypoxia [ 79 ] and cerebral ischemia [ 10 , 11 ] . in our previous study , three 
 nitroimidazole - based thioflavin - t derivatives were synthesized and radiolabeled 
 with iodine-131 ( see figure 1 ) : n -[4-(benzothiazol-2-yl)-phenyl]-3-(2-nitroimidazole-1-yl ) 
 propanamide ( 2npbta ) , n-[4-(benzothiazol-2-yl)phenyl]-3-(4-nitroimidazole-1-yl)-propanamide 
 ( 4npbta ) , and n-[4-(benzothiazol-2-yl ) 
 phe - nyl]-3-(4-nitroimidazole-1-yl)-n - methylpropanamide 
 ( 4n - pbta-1 ) . in vitro and in vivo results showed that they could bind to viable 
 hypoxic tumor cells . in this paper , their permeability across the bbb 
 into the normal brain and in vivo evaluation in the gerbil cerebral 
 ischemia models were investigated . no - carrier - added na[i ] ( aqueous solution ) was 
 obtained from china institute of atomic energy . 2npbta , 4npbta , and 4npbta-1 
 were synthesized and radiolabeled with iodine-131 in our laboratory . kunming mice were obtained from breeding center of the 
 institute of zoology and adult mongolian gerbils from breeding center of 
 capital university of medical sciences . all experiments were carried out 
 following the principles of laboratory animal care and the china law on the 
 protection of animals . radioactivity in the brain of the animals was assayed 
 using a cobra ii series auto - gamma counting system ( packard ) . brain uptake and clearance were performed using normal 
 kunming mice ( males ,  20 g ) . each 
 mouse received a 0.1 ml ( 2 ci , mbq ) dose 
 of [ i]2npbta , [ ] 4npbta , or [ i]4npbta-1 by tail vein injection . 
 such injection solution ( 0.1 ml ) was taken as standard for calculating the 
 percent injected dose per gram of tissue , that is , % id / g . at 2 and 30 minutes 
 postinjection , mice were killed without anesthesia by cervical dislocation in 
 groups of five . the brain uptake 
 ( the percent injected dose per gram of tissue , % id / g ) was calculated . the 
 2-to-30 minutes ratios of % id / g of the brain were calculated . the final results 
 were expressed as mean  standard 
 deviation ( sd ) . adult mongolian gerbils ( males ,  100 g ) were 
 used for cerebral ischemia models . a right common carotid artery ligation was 
 performed to produce cerebral hypoxia - ischemia ( hi ) as initially described by 
 levine and payan . gerbils were anesthetized intraperitoneally ( i.p . ) with 3.5% chloral hydrate ( 1 
 ml ) , and the four limbs were fixed . a midline anterior incision was made , the 
 right common carotid artery was isolated and ligated with 60 surgical sutures 
 distally and proximally . thereafter , the incision was closed , and the gerbils were allowed to awake . gerbils were ranked by the modified stroke index ( si ) described by ohno et al . . [ i]2npbta , [ i]4npbta , or [ i]4npbta-1 ( 0.5 ml , 10 ci , mbq ) was 
 injected i.p . into the gerbils . such injection solution ( 0.5 ml ) was taken as 
 standard for calculating the percent injected dose per gram of tissue , that is , 
 % id / g . the gerbils were sacrificed without 
 anesthesia by cervical dislocation in groups of three at 4 , 8 , and 12 hours 
 after injection . the whole brain was removed , placed on dry ice for about 2 
 minutes , and then cut in half along the cerebral longitudinal fissure . the right / left hemispheral 
 uptake ratios , that is , the ratios of ischemic brain to normal brain , were also 
 calculated . the final results were expressed as mean  standard 
 deviation ( sd ) . the observed significance level ( p value ) [ ] 2npbta ( 0.1 ml , 2 ci ) was 
 injected intraperitoneally ( i.p . ) into the gerbils subjected to right common 
 carotid artery ligation at 0 , 60 , 120 , 180 , and 240 minutes . such injection 
 solution ( 0.1 ml ) was taken as standard for calculating the percent injected 
 dose per gram of tissue , that is , % id / g . before sacrifice , gerbils were sacrificed ( no anesthesia ) by cervical dislocation 120 
 minutes after the final injection . the whole brain was removed , blotted free of 
 excess blood , placed on dry ice for about 2 minutes , and then sliced coronally 
 at approximately 3-mm intervals , yielding a total of five coronal slices , 
 designated a each slice was then cut in half 
 at the midsagittal plane , and the right and left halves were weighed and 
 radioactivity counted . high brain uptake and low nonspecific binding , as measured 
 by the ratio of brain uptake at 2 and 30 minutes , will generally improve the 
 quality of brain tomographic studies . it can be seen from table 1 that the brain uptake of 
 the three compounds was high at 2 minutes , and low binding at 30 minutes . as a 
 result , the ratio of brain uptake at 2 and 30 minutes for [ i]2npbta , [ i]4npbta , and [ i]4npbta-1 reached 6.2 , 9.7 , 
 and 5.4 , correspondingly . thus , these compounds showed not only good permeation 
 across the bbb into the brain at the early stage postinjection but also fast 
 clearance from the normal brain tissue soon , making them worthy of further 
 study as brain ischemia markers . the uptake of [ i]2npbta , [ i]4npbta , and [ i]4n - pbta-1 in the ischemic brain hemisphere 
 ( right ) and normal brain hemisphere ( left ) at 4 , 8 , and 12 hours after 
 administration is presented in table 2 . the right / left ( ischemic / normal ) 
 hemispheral uptake ratios were also calculated . the uptake in the right 
 hemisphere was higher than that in the left at 4 , 8 , and 12 hours postinjection 
 for [ i]2npbta . this indicated that 
 the clearance from ischemic brain tissue was slower than that from normal brain 
 tissue . this was attributed to the selective accumulation of 2-nitroimidazole 
 in hypoxic or ischemic conditions [ 15 , 16 ] . the right / left uptake ratios , that is , the uptake 
 ratios of ischemic to normal brain tissues were gradually increasing for [ i]2npbta , from 1.18 at 4 hours 
 to 1.76 at 12 hours . similar to the finding of read et al . that 30% of penumbral tissue of ischemic 
 stroke was present at an average of approximately 20 hours using the hypoxia 
 marker f - labeled fluoromisonidazole 
 , as for [ i]2npbta , the difference 
 between the uptake of the right hemisphere and the left hemisphere was 
 significant ( .05 > p > .01 ) at 12 hours , and the difference of the right / left 
 uptake ratios between 12 hours and 4 hours was very significant ( p < .01 ) . unfortunately , as for [ i]4npbta and [ i]4npbta-1 , the differences 
 between ischemic and normal brain tissues were not significant among all groups 
 ( p > .05 ) . figure 2 shows the uptake of [ i]2npbta in coronal brain 
 slices from 4 gerbils subjected to right common carotid ligation after multiple 
 injections . the brain of 
 each gerbil was divided into five 3-mm coronal sections , designated a the stroke indices ranging from 0 to 13 were indicated 
 above the histograms for each animal . increased uptake of [ i]2npbta in ischemic 
 hemispheres was found . the right / left hemisphere uptake ratios were 1.1 , 0.9 , 
 0.9 , 1.1 , and 0.9 from a to e for stroke index = 0 and 1.2 , 1.2 , 1.1 , 1.3 , 1.1 
 for stroke index = 4 . for stroke indices = 11 and 13 , they were 1.5 , 2.0 , 1.8 , 
 1.7 , 1.5 and 1.3 , 2.4 , 2.2 , 2.0 , 1.4 . in the gerbil with no evidence of 
 ischemia ( stroke index 0 ) , there was no evident right / left difference in any 
 coronal sections . in the gerbil with a stroke index of 4 the gerbils with markedly symptomatic ischemia ( stroke 
 indices 11 or 13 ) showed a 2-fold or 2.4-fold higher uptake in the midparietal 
 region of the right hemisphere compared with the left . this confirmed that 
 there was greater uptake of [ i]2npbta in the right 
 hemisphere compared with the left and verified that there was a trend for 
 increased uptake with increasing stroke index . our data supported the result 
 reported by hoffman et al . through the study of 
 [ h]misonidazole   that the right / left 
 hemisphere uptake ratios correlated positively with the severity of the stroke . for the gerbils with stroke index 11 or 13 , the 
 right / left hemisphere uptake ratios were modest at the most anterior coronal 
 sections , that is , section a , the rostral end . the two anterior cerebral arteries 
 of the gerbils fuse in the interhemispheric fissure to form a single 
 pericallosal artery [ 1820 ] . ischemia may be developed 
 in the anterior brain regions on the nonligated side following the loss of the 
 contributing anterior cerebral flow from the opposite internal carotid 
 circulation . thus , the rostral end of the left brain of the most symptomatic gerbil also 
 showed an increase in uptake , compared with the corresponding coronal section 
 in gerbil with very low stroke index . the gerbil has an incomplete circle of 
 willis and , after carotid ligation , may develop severe ischemia in the 
 forebrain . the cerebellum and brain stem , which are supplied by the vertebral 
 arteries , are included in the posterior sections of the brain . thus , the right / left difference was also 
 modest at the caudal end , that is , the section e , and the coronal brain 
 sections consistently showed a decreasing rostal - to - caudal binding of [ i]2npbta , from b to e. 
 different from the result of hoffman et al .   that there was no difference between right and left 
 at the caudal ends , ours also showed difference at slice e , they were 1.5 fold 
 and 1.4 fold for stroke indices = 11 and 13 . the unique anatomical feature of the gerbil made them 
 widely used as a model in global ischemia [ 18 , 19 , 21 ] . 
 unlike rats , gerbils do not have a posterior communicating artery , that is , the 
 circle of willis is incomplete and there is incomplete anastomosis of the 
 anterior cerebral arteries . therefore , the blood supply of each hemisphere is 
 isolated from the contralateral carotid and basilar arteries . thus , global 
 cerebral ischemia in gerbils can be induced by bilateral common carotid artery 
 occlusion or unilateral common carotid occlusion . ligation of one carotid 
 artery causes ischemia in the ipsilateral hemisphere , while the other side is 
 unaffected , providing neighboring normal tissue as an internal control . many 
 investigators have demonstrated that unilateral carotid occulation produces 
 homolateral ischemia and/or infarction in approximately 3050% of adult male 
 gerbils [ 1820 ] . this study indicated that [ i]2npbta , [ i]4npbta , and [ i]4npbta-1 showed good 
 permeation across the bbb into the brain and fast washout from the normal brain 
 tissue . this study also demonstrated a specific location of [ i]2npbta in the cerebral 
 ischemic tissue . these results represented a first step toward cerebral 
 ischemia markers of 2npbta and made it worthy of further investigation .