Middle cerebral artery occlusion in the young rat

Fetal neocortical grafts placed in brain infarcts do not improve paw-reaching deficits in adult spontaneously hypertensive rats

The aim was to study if neural grafts placed brain infarcts could improve functional recovery. The middle cerebral artery was occluded (MCAO) in 19 spontaneously hypertensive rats. Nine rats were sham operated. Twelve to 16 days after the ischemic insult, 9 of the MCAO rats received transplants of dissociated fetal neocortical tissue (MCAO-T) and 1, 3 and 6 months after transplantation surgery, the rats were behaviorally evaluated by a test for forelimb function. Infarct and transplant sizes were measured morphometrically. The remaining volume of the infarcted hemisphere was 66 +/- 7% (mean +/- SD) in the MCAO group and 71 +/- 9% in the MCAO-T group of the non-operated hemisphere. All grafted rats had surviving transplants. Contralateral to the lesion, paw-reaching was highly impaired in both infarcted groups compared with sham-operated controls with no significant difference between MCAO and MCAO-T. The lesion size correlated significantly with contralateral paw-reach performance at all test periods. We conclude that neocortical grafts did not alleviate the impaired forepaw function.

Local hemodynamic changes during transient middle cerebral artery occlusion and recirculation in the rat: a [14C]iodoantipyrine autoradiographic study

We evaluated acute alterations of local cerebral perfusion following 30 min of transient right proximal middle cerebral artery (MCA) clip-occlusion in the rat and following two intervals of postischemic reperfusion. Local cerebral blood flow (lCBF) was assessed by [14C]iodoantipyrine autoradiography. Brain temperature was controlled at 35.5-36.5 degrees C throughout the experiment. We measured lCBF in four groups of rats: (a) sham-operated controls (n = 5), (b) following 30 min MCA occlusion (n = 5), (c) following 30 min of MCA occlusion with 15-min reperfusion (n = 6) and (d) following 30 min of MCA with 120-min reperfusion (n = 6). lCBF was measured in seven regions of the ischemic and non-ischemic hemispheres. MCA occlusion induced an ipsilateral reduction of lCBF, which was most severe in the parietal cortex (8.4 +/- 4.0% of control, mean +/- S.D.), and dorsolateral caudoputamen (20.0 +/- 13.4% of control). lCBF in the non-ischemic hemisphere and in ipsilateral regions lying outside the MCA territory also decreased significantly. lCBF recovery was incomplete when assessed following only 15 min of reperfusion. Reperfusion of 120 min led to return of cortical CBF to control levels, but lCBF in the caudoputamen remained depressed (50-55% of control values). Caudoputaminal CBF and cortical CBF values were highly correlated with one another under normal and ischemic conditions, but this correlation was disrupted following reperfusion. On the basis of these results, we speculate that, if a means were found to enhance the early recovery of lCBF following transient ischemia, this might expand the therapeutic window of opportunity for the institution of other neuroprotective strategies.

Effects of central inhibition of nitric oxide synthase on focal cerebral ischemia in rats

We have investigated whether central inhibition of nitric oxide synthase (NOS) could modify the tissue damage of focal cerebral ischemia produced by occlusion of the middle cerebral artery (MCA) in rats. NG-Nitro-L-arginine methyl ester (L-NAME) was administered intracerebroventricularly at two doses 15 min prior to occlusion of the MCA, as well as 4 and 24 h following occlusion. After the injection of L-NAME, the catalytic activity of the constitutive NOS, considered to be mainly neuronal, was effectively suppressed in the subcortical gray matter bilaterally, but not in the ischemic territory. Seven days after the MCA occlusion, the brains were evaluated for histopathologic damage. High-dose administration of L-NAME (120 micrograms/kg 15 min prior to MCA occlusion, followed by 150 micrograms/kg 4 and 24 h after occlusion) produced an enlargement of the infarct area and increased the volume of ischemic damage. These results indicate that extensive inhibition of NOS by a central route can increase the cerebral infarct size in focal ischemia even if NOS is not inhibited in the ischemic tissue and suggest that NO may also play a potentially beneficial role as well as a neurodestructive role in the pathophysiological mechanisms of focal cerebral ischemia.

A new model of neonatal stroke: reversible middle cerebral artery occlusion in the rat pup

Neonatal stroke remains a complex pathophysiologic process that is poorly understood and difficult to investigate. The primary animal model used to study this phenomenon is that of unilateral carotid artery ligation with 2-3 hours exposure to severe hypoxia. A new model of neonatal stroke was developed based on transient middle cerebral artery occlusion without craniectomy. In this model a #6-0 (0.07 mm) nylon filament is passed via the carotid artery to occlude reversibly the middle cerebral artery for 4 hours under conditions of normoxia in 14- to 18-day-old spontaneously hypertensive rat pups. After removal of the filament and reperfusion for 24 hours, the infarct volume was determined using the mitochondrial stain, 2,3,5-triphenyltetrazolium chloride. Using this technique, a neocortical and caudoputamenal infarct affecting 49% of hemispheric volume that measured 180 +/- 29 mm3 (hemisphere volume = 359 +/- 16 mm3, mean +/- SEM) was created in 90% of animals (n = 8) undergoing this procedure. This model has the advantage of being relatively noninvasive, of not requiring global exposure of brain to hypoxia, and of using temporary rather than permanent occlusion. This technique should improve the ability to study the acute and long-term pathophysiology of neonatal stroke, particularly the phenomenon of reperfusion injury, as well as its sequelae in the developing nervous system.

A modified rat model of middle cerebral artery thread occlusion under electrophysiological control for magnetic resonance investigations

Previous magnetic resonance (MR) investigations of middle cerebral artery (MCA) occlusion in rats were limited by the lack of early post-occlusion MR measurements and/or electrophysiological monitoring. Therefore, we have developed a technique which allows to perform MCA occlusion inside the magnet under simultaneous recording of EEG and direct current (DC) potentials for monitoring the ischemic insult. Rats underwent intraluminal thread occlusion of the right MCA inside the MR tomograph via a catheter extension device, while EEG and DC potentials were recorded by non-magnetic graphite electrodes. The thread was slowly advanced until electrophysiological changes appeared. Diffusion-weighted MR images (DWI) were obtained before and repeatedly after MCA occlusion for up to 7 h. Thereafter, rat brains were frozen in situ or fixed by transcardiac perfusion and investigated by biochemical and histological techniques. In 15 of 18 animals (83%), MCA thread insertion caused immediate EEG changes and a negative DC potential shift at 4.4 +/- 1.8 min (mean +/- SD) after occlusion. In all animals with electrophysiological changes, signal intensity of DWI began to increase within the MCA territory at 12-14 min post-occlusion (the end of the first measurement), and continued to rise throughout the observation period. Ischemia was confirmed by demonstrating focal areas of energy depletion on ATP images. In the animals without electrophysiological changes, DWI or biochemical alterations were absent or confined to the central part of caudate-putamen. The histological lesion area of successfully occluded animals amounted to 70.1 +/- 5.8% of the ipsilateral hemisphere at the level of caudate-putamen.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino acid and purine release in rat brain following temporary middle cerebral artery occlusion

Excitatory amino acid release and neurotoxicity in the ischemic brain may be reduced by endogenously released adenosine which can modulate both glutamate or aspartate release and depress neuronal excitability. The present study reports on the patterns of release of glutamate and aspartate; the inhibitory amino acids GABA and glycine; and of the purine catabolites adenosine and inosine from the rat parietal cerebral cortex during 20 and 60 min periods of middle cerebral artery (MCA) occlusion followed by reperfusion. Aspartate and glutamate efflux into cortical superfusates rose steadily during the period of ischemia and tended to increase even further during the subsequent 40 min of reperfusion. GABA release rose during ischemia and declined during reperfusion, whereas glycine efflux was relatively unchanged during both ischemia and reperfusion. Adenosine levels in cortical superfusates rose rapidly at the onset of ischemia and then declined even though MCA occlusion was continued. Recovery to pre-occlusion levels was rapid following reperfusion. Inosine efflux also increased rapidly, but its decline during reperfusion was slower than that of adenosine.

Calcium accumulation following middle cerebral artery occlusion in stroke-prone spontaneously hypertensive rats

Delayed neuronal damage in the ischemic region of the rat brain following middle cerebral artery (MCA) occlusion in stroke-prone spontaneously hypertensive rats was studied. The distribution of neuronal damage was determined by 45Ca autoradiography. Accumulation of 45Ca was observed in the corpus callosum and ipsilateral cerebral cortex immediately following MCA occlusion. After 3 days of occlusion, 45Ca had accumulated in the ipsilateral pyramidal tract, the ventral posterior nucleus of the thalamus, and the lateral portion of the striatum. Significant accumulation of 45Ca was observed in the same areas after 7 and 14 days of occlusion. Next the effect of MK-801 on accumulation of 45Ca after MCA occlusion was examined using the same technique. MK-801 (0.5-10 mg/kg i.v.) or saline was administered 15 min before MCA occlusion, and volumes of accumulation of 45Ca were calculated 1 week after ischemic insults. MK-801 significantly reduced 45Ca uptake in the cortex, striatum, and thalamus. Furthermore, there was a strong statistical correlation between the volume of accumulation of 45Ca in the cortex and that in the thalamus (r = 0.8974; p < 0.001; n = 25). We speculate that delayed neuronal damage in the corpus callosum, ipsilateral pyramidal tract, and thalamus may be caused by secondary neuronal degeneration. However, neuronal damage in the striatum, a segment not supplied by the MCA, may be related to excessive release of glutamate.

Failure to prevent selective CA1 neuronal death and reduce cortical infarction following cerebral ischemia with inhibition of nitric oxide synthase

We investigated the putative role of nitric oxide in the expression of neuronal injury following both transient severe forebrain ischemia (CA1 neuronal injury) and transient or permanent middle cerebral artery occlusion (neocortical pannecrosis). Using the four-vessel occlusion model and increasing doses of N-omega-nitro-L-arginine, 2-40 mg/kg, we were unable to demonstrate any reduction in the percentage of CA1 cells injured following 10 min of transient severe forebrain ischemia followed by seven days of reperfusion. Higher doses proved toxic insofar as they increased the mortality following the ischemic insult. Saline-treated animals (n = 8) had 77 +/- 10% CA1 injury while those treated with 2 mg/kg of nitro-arginine i.v. had 80 +/- 7% (n = 7), and those with 10 mg/kg i.v. had 78 +/- 11% (n = 8). Two of five rats given 20 mg/kg i.v., three of eight given 40 mg/kg i.v., and two of six given 10 mg/kg i.v. followed by 3 x 10 mg/kg i.p., died. Of those treated with high-dose nitro-arginine and which survived ischemia and seven days' reperfusion, no significant reduction in CA1 injury was detected. Wistar rats and spontaneously hypertensive rats treated with either saline or nitro-arginine i.v. were exposed to 2 h of transient middle cerebral artery occlusion followed by 22 h of reperfusion. There were seven animals in each group. Wistars treated with saline had 198 +/- 67 mm3 (mean +/- S.D.) of neocortical infarction, and those treated with 10 m/kg of nitro-arginine i.v. had 199 +/- 93 mm3. Spontaneously hypertensive rats, transiently ischemic, treated with saline had 164 +/- 25 mm3 of infarct volume, while those treated with 2 mg/kg i.v. had 151 +/- 53 mm3, and those treated with 10 mg/kg i.v. had 145 +/- 29 mm3. Animals treated with 40 mg/kg i.v. had a nonsignificantly larger mean infarct volume (191 +/- 81 mm3). High dose nitro-arginine caused an increase in hypertension in the spontaneously hypertensive rats and increased the severity of focal ischemia as measured by intra-ischemic regional cerebral blood flows. A final group of seven spontaneously hypertensive rats underwent permanent middle cerebral artery occlusion and repeated dosing with N-omega-nitro-L-arginine i.p. In these animals an infarct volume of 234 +/- 60 mm3 was observed, which was again not statistically different from saline-treated controls (208 +/- 43 mm3, n = 7).(ABSTRACT TRUNCATED AT 400 WORDS)

Delayed treatment with AMPA, but not NMDA, antagonists reduces neocortical infarction

We tested the abilities of two potent non-N-methyl-D-aspartate (non-NMDA) glutamate antagonists [2,3-dihydroxy-6-nitro-7-sulfamoylbenzo(F)quinoxaline (NBQX)] and [1-(4-aminophenyl)-4-methyl-7,8-methylene-dioxy-5H-2,3-benzodiazep ine hydrochloride (GYKI 52466)] to reduce neocortical infarction following 2 h of transient middle cerebral artery occlusion in a hypertensive stroke model in the rat and compared these effects against, and in combination with, a potent NMDA antagonist [(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-amine maleate (MK-801)]. In Expt. 1, an already established cytoprotective dose of Na(+)-NBQX (30 mg/kg i.p. x 3) was compared with saline (1 ml), the NMDA antagonist MK-801 (1 mg/kg i.p. x 3), and a combination of the same doses of both NBQX and MK-801. Initial doses were delayed to 90 min following occlusion with subsequent injections at the time of reperfusion and 30 min following reperfusion. Saline-treated rats sustained 181 +/- 32 mm3 (n = 15) of neocortical infarction (mean +/- SD). This was significantly reduced by NBQX to 137 +/- 25 mm3 (n = 15, p < 0.05) of damage. Neither MK-801 (170 +/- 33 mm3; n = 11) nor the combination of MK-801 and NBQX (169 +/- 20 mm3; n = 6) proved to be cytoprotective when given with a 90-min delay. In Expt. 2, NBQX (30 mg/kg) was dissolved (6 mg/ml) in 5% dextrose and compared with both saline and dextrose (1.2 ml) i.v. infusions given over a 4-h period starting 1 h after occlusion. Saline-treated rats had a mean infarct of 183 +/- 27 mm3 (n = 6), dextrose-treated had 200 +/- 30 mm3 (n = 9), while for NBQX-treated rats it was reduced to 129 +/- 60 mm3 (n = 10, p < 0.05). Intravenous NBQX precipitated into the renal tubules, causing nephrotoxicity. In Expt. 3, rats were given either saline (1 ml i.p.) or GYKI 52466 (10 mg/kg i.p.) at 30 and 90 min following occlusion and at 30, 90, and 150 min following reperfusion. Saline-treated rats sustained 187 +/- 27 mm3 of neocortical infarction (n = 7), while those treated with GYKI 52466 were protected, with 139 +/- 38 mm3 of infarction (n = 7, p < 0.05). A clinically useful role for alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate antagonists in embolic stroke is envisaged if nontoxic drugs can be developed, since cerebroprotection was achieved with delayed treatment with both of these lead compounds.

A brief hypoperfusion precedes spreading depression if nitric oxide synthesis is inhibited

Spreading cortical depression (SCD) alters cerebral blood flow by mechanisms that are not well understood. To investigate the role of the likely endothelium-derived relaxing factor, nitric oxide, in the blood flow changes occurring during SCD in awake rats, nitric oxide synthesis was blocked using N omega-nitro-L-arginine methyl ester (L-NAME). During SCD there is an initial hyperperfusion followed by a longer-lasting hypoperfusion. Treatment with L-NAME, 30 mg/kg, reduced resting cerebral blood flow globally. During SCD, L-NAME treatment produced an additional brief phase of hypoperfusion which preceded the initial hyperperfusion. The magnitude of the initial hyperperfusion was less than expected. The subsequent longer-lasting hypoperfusion was unchanged. Nitric oxide plays an important role in the regulation of cerebral blood flow during SCD.

A reproducible model of reversible, focal, neocortical ischemia in Sprague-Dawley rat

A reproducible model of reversible, focal ischemia was developed for use with the normotensive, Sprague-Dawley rat. Blood flow to the left cerebral hemisphere was interrupted by occluding simultaneously the left middle cerebral artery and both carotid arteries (CCA). The arterial occlusion lasted for 1, 2 or 3 hours after which animals survived for 3 days. The volume of brain infarction was determined utilizing computer-assisted measurements of serial brain sections stained with triphenyltetrazolium. Tissue infarctions of variable size were observed following arterial occlusions which persisted 1 or 2 hours. In contrast, remarkably-consistent infarction size was obtained following a three hours period of occlusion. Tissue edema was also estimated by measuring the volumes of the two hemispheres and expressing these values as a ratio for each animal. The volume ratio was significantly greater in the 3 hour ischemic group, indicating the occurrence of edema in the infarcted hemisphere. These results demonstrate that reversible vascular occlusion in the normal, Sprague-Dawley rat results in consistent amounts of tissue infarction. This approach represents an attractive model system for studying the pathophysiological effects of transient, focal ischemia and for testing the effects of putative, therapeutic strategies.

Effects of intermittent reperfusion during temporal focal ischemia

There is controversy regarding the role of intermittent reperfusion employed as a cerebroprotective measure when temporary arterial occlusion is necessary during repair of difficult aneurysms. The intraluminal suture middle cerebral artery (MCA) occlusion technique was used in 23 Wistar rats under barbiturate anesthesia to induce 60, 90, or 120 minutes of uninterrupted MCA occlusion. The total infarcted areas obtained were compared to those occurring in 27 animals subjected to identical cumulative ischemic periods but with 5 minutes of reperfusion after every 10-minute ischemic period. The mean total infarcted areas in the groups with 60-minute (1.8 +/- 0.89 sq mm), 90-minute (1.08 +/- 1.02 sq mm), and 120-minute (8.72 +/- 5.89 sq mm) intermittent reperfusion were significantly smaller than those occurring in the 60-minute (12.02 +/- 3.10 sq mm), 90-minute (11.54 +/- 2.68 sq mm), or 120-minute (30.43 +/- 6.51 sq mm) control groups, respectively (p < 0.05). Furthermore, there was no difference in the occurrence of blood-brain barrier breakdown, intraparenchymal hemorrhage, hemispheric edema, or seizures between control and intermittent reperfusion groups. The results support the hypothesis that intermittent reperfusion is beneficial if vessel occlusion is required during aneurysm repair.

Middle cerebral artery occlusion in rats: a neurological and pathological evaluation of a reproducible model

Middle cerebral artery occlusion (MCAO) in rats produces an infarct of varying size. We examined three factors that may influence this variability: animal weight, vascular anatomy, and extent of occlusion in rats undergoing MCAO. We also developed a four-point neurological evaluation scale and validated its usefulness by comparing it with a four-grade pathological determination of the size of the infarct. Of 82 animals subjected to a standard MCAO, 34 developed small cortical infarcts (pathological grades I-II; infarct size less than 25 mm2, 6-17% of the ipsilateral cortex surface area), and 48 large infarcts (pathological grades III-IV, infarct size greater than 25 mm2, 20-56% of surface area). We were able to predict the size of infarction from the neurological evaluation in 83% of the animals, and this accuracy reached 91% when grades I and II and III and IV were considered together (P less than 0.001). In 41 animals subjected to a more extensive vascular occlusion, 89% exhibited large infarcts. Four vascular patterns were identified but none played a significant role in the incidence or size of the cortical stroke. However, rats weighing less than 300 g showed a smaller lesion size than did rats greater than 300 g. Our proposed new MCAO technique appears useful in reproducing large-sized infarcts of the frontoparietal cortex.

Genetic hypertension and increased susceptibility to cerebral ischemia

A review of the sensitivity of genetically hypertensive rats to cerebral ischemia was presented together with original data describing the systematic comparison of the effects of focal ischemia (permanent and temporary with reperfusion) performed in hypertensive and normotensive rats (i.e., blood pressures verified in conscious instrumented rats). Microsurgical techniques were used to isolate and occlude the middle cerebral artery (MCAO) of spontaneously hypertensive (SHR), Sprague-Dawley (SD) and Wistar Kyoto (WKY) rats at the level of the inferior cerebral vein. Following permanent (24 h) MCAO, persistent and similar decreases in local microvascular perfusion (i.e., to 15.6 +/- 1.7% of pre-MCAO levels) were verified in the primary ischemic zone of the cortex for all strains using Laser-Doppler flowmetry. A contralateral hemiplegia that occurred following MCAO, evidenced by forelimb flexion and muscle weakness, was greater in SHR (neurological grade = 2.0 +/- 0.1) than SD (1.0 +/- 0.4) or WKY (0.7 +/- 0.4) rats (N = 7-9, p less than 0.05). SHR also exhibited sensory motor deficits following MCAO compared to sham-operation, with decreased normal placement response of the hindlimb (% normal = 20 vs. 83, N = 23-30, p decreased rota-rod (41 +/- 7 vs. 126 +/- 19 on rod, N = 10-15, p less than 0.05) and balance beam (25 +/- 5 vs. 116 +/- 29 s on beam, N = 5-7, p less than 0.05) performance. However, an index of general motor activity was not affected by permanent MCAO. Triphenyltetrazolium-stained forebrain tissue analyzed by planimetry revealed a significantly larger and more consistent cortical infarction in SHR (hemispheric infarction = 27.9 +/- 1.5%) compared to SD (15.4 +/- 4.1%) and WKY (4.0 +/- 2.4%) rats (N = 7-9, p less than 0.05), occupying predominantly the frontal and parietal areas. Also, a significant degree of ipsilateral hemispheric swelling (4.6 +/- 0.9%, N = 7-9, p less than 0.05) and increased brain water content (78.4 +/- 0.3% to 80.4 +/- 0.2%, N = 8-9, p less than 0.05) was identified in SHR that was not observed in SD or WKY rats. A novel model of temporary MCAO also was evaluated in the hypertensive and normotensive rat strains. Initially, the effect of increasing MCAO-time followed by 24 h reperfusion in SHR was studied. During temporary MCAO (20 to 300 min), persistent and stable decreases in local microvascular perfusion (i.e., to 15-20% of pre-MCAO levels) were verified in the primary ischemic zones of the cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

The CBF threshold and dynamics for focal cerebral infarction in spontaneously hypertensive rats

Two strategies were used to estimate the blood flow threshold for focal cerebral infarction in spontaneously hypertensive rats (SHRs) subjected to permanent middle cerebral artery and common carotid artery occlusion (MCA/CCAO). The first compared the volume of cortical infarction (24 h after ischemia onset) to the volumes of ischemic cortex (image analysis of [14C]iodoantipyrine CBF autoradiographs) perfused below CBF values less than 50 (VIC50) and less than 25 ml 100 g-1 min-1 (VIC25) at serial intervals during the first 3 h of ischemia. The infarct process becomes irreversible within 3 h in this model. In the second, measurements of CBF at the border separating normal from infarcted cortex at 24 h after ischemia onset were used as an index of the threshold. During the first 3 h of ischemia, VIC50 increased slightly to reach a maximum size at 3 h that closely matched the 24 h infarct volume. VIC25, in contrast, consistently underestimated the infarct volume by a factor of 2-3. CBF at the 24 h infarct border averaged 50 ml 100 g-1 min -1. Taken together, the results indicate that the CBF threshold for infarction in SHRs approaches 50 ml 100 g-1 min-1 when ischemia persists for greater than or equal to 3 h. This threshold value is approximately three times higher than in primates. Since cortical neuronal density is also threefold greater in rats than in primates, the higher injury threshold in the rat may reflect a neuronal primacy in determining the brain's susceptibility to partial ischemia.

Regional expression of heat shock protein-70 mRNA and c-fos mRNA following focal ischemia in rat brain

In situ hybridization was used to estimate regional levels of heat shock protein-70 (HSP-70) mRNA and c-fos mRNA in two related models of focal cerebral ischemia. In the first model, permanent occlusion of the distal middle cerebral artery (MCA) alone caused a patchy increase in HSP-70 mRNA by 1 h in the central zone of the MCA territory of the ipsilateral neocortex. Tissue levels of HSP-70 mRNA continued to increase for several hours and remained elevated at 24 h. In contrast to the focal expression of HSP-70, c-fos mRNA was increased throughout the ipsilateral cerebral cortex by 15 min and remained elevated for least 3 h. The wide distribution of c-fos expression suggests it may have been caused by spreading depression. In the second model, severe focal ischemia was produced with a combination of transient (1-h) bilateral carotid artery occlusion and permanent MCA occlusion. Combined occlusion for 1 h without reperfusion caused expression of HSP-70 mRNA only in regions adjacent to the central zone of the MCA territory of the neocortex. However, reperfusion of the carotids for 2 h generated intense expression of HSP-70 mRNA throughout most of the ipsilateral cerebral cortex, white matter, striatum, and hippocampus. The wide-spread increase in HSP-70 mRNA suggests that reperfusion triggered expression in all previously ischemic regions. However, at 24 h of reperfusion, increased levels of HSP-70 mRNA were restricted primarily to the ischemic core of the neocortex. These results suggest that expression of HSP-70 mRNA is prolonged in regions undergoing injury, but is transient in surrounding regions that recover.

Cortical hypoperfusion following spreading depression is not altered by tirilazad mesylate (U-74006F) in awake rats

The 21-aminosteroid antioxidant tirilazad mesylate (U-74006F) blocks the delayed hypoperfusion associated with spreading cortical depression (SCD) in anesthetized rats. Because the resting vascular tone influences the blood flow response to SCD, the effect of this drug was reassessed in awake rats. In this state, tirilazad mesylate did not eliminate cerebral hypoperfusion following SCD. Oxygen radical-induced lipid peroxidation may not mediate cerebral hypoperfusion after SCD in awake rats.

Deoxycoformycin and oxypurinol: protection against focal ischemic brain injury in the rat

We have previously demonstrated that oxypurinol (40 mg/kg i.p.), a xanthine oxidase inhibitor, can reduce focal ischemic brain injury in the rat when applied pre-ischemically. By using a model of occlusion of the middle cerebral artery (MCA) in tandem with occlusion of the ipsilateral carotid artery, the present study further demonstrates that delayed (60 min) administration of oxypurinol also exhibits a protective action on ischemic damage in the stroked rat brain. Oxypurinol significantly reduced the ischemic cerebral infarct zone by preventing the development of brain damage primarily in areas distant to the central lesion core. A corresponding amelioration of brain swelling and attenuation of neurological deficits were evident. Similar protection against focal ischemic brain damage was evident when the adenosine deaminase inhibitor, deoxycoformycin (500 micrograms/kg), was administered prior to the onset of ischemia. However, with delayed (60 min) administration deoxycoformycin had no protective effect. These findings support the hypothesis that manipulation of adenosine catabolism can be an effective therapeutic approach to the prevention or treatment of brain injuries, such as those occurring during ischemic stroke or cardiac arrest.

Oxypurinol reduces focal ischemic brain injury in the rat

When measured within 2 days of a unilateral occlusion of the middle cerebral artery (MCA) combined with tandem occlusion of the ipsilateral common carotid artery in rats, contralateral neurological deficits were detectable, with brain swelling and a consistent degree of neocortical infarction in the ipsilateral hemisphere. Oxypurinol (40 mg/kg i.p. administered 0.5 h prior to, and 24 h after, the onset of focal ischemia) significantly reduced the development of the ischemic infarct (P less than 0.001); attenuated tissue swelling (P less than 0.01) and ameliorated the neurological deficits (P less than 0.05). These findings suggest that this compound may be useful for the prevention or treatment of ischemic brain injuries, such as those occurring during stroke.

Asphyctic lesion: proliferation of tyrosine hydroxylase-immunoreactive nerve cell bodies in the rat substantia nigra and functional changes in dopamine neurotransmission

Asphyxia was induced in male rat pups by performing a delayed cesarean section on pregnant Sprague-Dawley rats. Oxygen saturation and heart rate were recorded during induction of asphyxia. Animals were sacrificed at 3 weeks of age. Brain sections were stained for tyrosine-hydroxylase (TH), dopamine-and-cyclic-AMP-regulated-phosphoprotein-32 (DARPP-32) immunoreactivity (IR) and thionein. Increasing time of asphyxia caused a reduction in the number of nerve cell bodies in the CA1 and CA3 regions of the hippocampus reflecting neuronal death. Furthermore, asphyxia resulted in an increased number of TH-IR nerve cell bodies indicative of a proliferation of dopaminergic neurons in the zona compacta of the substantia nigra. Finally, a significant decrease in rearing was observed in asphyctic animals during the habituation phase, as well as following apomorphine-induced (1 mg/kg s.c.) postsynaptic dopamine receptor stimulation. On the other hand, the apomorphine-induced increase in locomotion was enhanced in asphyctic animals. The implications of these findings for hyperkinesia and attention deficits in disorders resulting from asphyxia are discussed.

Effects of the calcium antagonist nilvadipine on focal cerebral ischemia in spontaneously hypertensive rats

We studied the efficacy of preischemic and postischemic systemic treatment with a new calcium antagonist nilvadipine in a permanent focal cerebral ischemia model of spontaneously hypertensive rats. Rats that underwent microsurgical middle cerebral artery occlusion were blindly assigned to a single intraperitoneal injection of nilvadipine (0.32 mg/kg) or the same amount of polyethylene glycol either 15 minutes before, immediately after, 1 hour after, or 3 hours after occlusion of the left middle cerebral artery. Neurologic conditions of rats were closely examined, and rats were killed 24 hours later. Removed brains were sliced coronally, stained with triphenyltetrazolium chloride, and the size of infarct was determined. Although no neurologic improvements were observed in the treated rats, the area of infarcts was significantly reduced in the groups treated before, immediately after, and 1 hour after occlusion of the middle cerebral artery. Treatment started 3 hours after occlusion was ineffective.

Regional cerebral blood flow during spreading cortical depression in conscious rats

Spreading cortical depression (SCD) of EEG activity was induced in one cerebral hemisphere of conscious restrained rats by direct current stimulation of the lateral frontal cortex. Regional CBF was measured using [14C]iodoantipyrine and brain dissection. An early phase of increased CBF was not measured in conscious rats, but an early relative hyperperfusion was measured if the resting CBF was first reduced by treatment with pentobarbital or indomethacin. A long-lasting reduction in CBF was measured in conscious rats following the passage of SCD. This flow reduction resolved after 3 h. In conscious rats, CBF decreased in the striatum and thalamus ipsilateral to the SCD, paralleling the CBF changes occurring in the cortex. The CBF change in these deep structures was abolished by pentobarbital. An early transient increase in regional CBF was measured in the cerebral cortex contralateral to the hemisphere involved with SCD in conscious rats. This early contralateral hyperperfusion was also abolished by pentobarbital or indomethacin but not by atropine or propranolol. The vascular response to SCD in conscious rats differs from that which occurs in anesthetized rats.

Protective effects of minaprine in infarction produced by occluding middle cerebral artery in stroke-prone spontaneously hypertensive rats

1. We examined the effects of minaprine on cerebral infarction produced by occluding of unilateral middle cerebral artery (MCA) above the rhinal fissure in stroke-prone spontaneously hypertensive rats (SHRSP). 2. Oral administration of minaprine (60 mg/kg/day) and vehicle were started 30 min after the occlusion of MCA, and continued for 6 days. 3. The brain was dissected out and 36 coronal multiple sections of the whole brain were histologically prepared to determine the location and extension of infarction. 4. The infarcted area produced by the occlusion of MCA was limited to the cerebral cortex. 5. Body weight of the minaprine-treated rats gradually decreased within 4 days after the occlusion of MCA and thereafter increased, whereas in the vehicle-treated rats, there was a gradual decrease during the experimental period. 6. Size of the infarcted area was serially measured, in each section, using a microcomputer imaging device. In all animals with an occluded MCA, there was a typical pattern of ischemic damage. 7. Post-treatment of MCA occluded SHRSP with minaprine resulted in reduction in infarct size, as compared to findings in the vehicle-treated controls. 8. The pharmacological and histopathological effects of minaprine on the progress of cerebral infarction produced by the occlusion of MCA in SHRSP are discussed.

Nimodipine pretreatment improves cerebral blood flow and reduces brain edema in conscious rats subjected to focal cerebral ischemia

The effect of nimodipine pretreatment on CBF and brain edema was studied in conscious rats subjected to 2.5 h of focal cortical ischemia. An infusion of nimodipine (2 micrograms/kg/min i.v.) or its vehicle, polyethylene glycol 400, was begun 2 h before the ischemic interval and was continued throughout the survival period. Under brief halothane anesthesia, the animals' right middle cerebral and common carotid arteries were permanently occluded, and 2.5 h later, they underwent a quantitative CBF study ([14C]iodoantipyrine autoradiography followed by Quantimet 970 image analysis). Nimodipine treatment improved blood flow to the middle cerebral artery territory without evidence of a "vascular steal" and reduced the volume of the ischemic core (cortex with CBF of less than 25 ml/100 g/min) and accompanying edema by approximately 50% when compared with controls (p = 0.006 and 0.0004, respectively). Mild hypotension induced by nimodipine did not aggravate the ischemic insult. The ischemic core volumes, however, were 50-75% smaller than the 24-h infarct volumes generated in a similar paradigm that demonstrated 20-30% infarct reduction with continuous nimodipine treatment. These results suggest that nimodipine pretreatment attenuates the severity of early focal cerebral ischemia, but that with persistent ischemia, cortex surrounding the ischemic core undergoes progressive infarction and the early benefit of nimodipine treatment is only partly preserved.

Autonomic and myocardial changes in middle cerebral artery occlusion: stroke models in the rat

Stroke models in larger animals such as the cat, dog and monkey are becoming increasingly more expensive and less readily available. However, the rat is an excellent model for focal cerebral ischemia. Rats are readily available, inexpensive and their neuroanatomy and brain function have been studied extensively. Increases in plasma catecholamines and myocardial damage have been observed in clinical stroke. We examined autonomic and myocardial changes in two rat stroke models. In one model only the middle cerebral artery was occluded (MCAO) while the other model involved occlusion of both the MCA and the common carotid artery (MCAO/CCAO). Arterial blood pressure and heart rate were monitored continuously in 25 male rats (326-430 g) that underwent one of the following procedures: (1) MCAO only; (2) MCAO/CCAO; (3) CCAO only; and (4) sham occlusions (SHAM). Arterial blood samples (0.5 ml) for radioenzymatic assay of norepinephrine (NE) and epinephrine (E) were taken twice before the occlusions and at 90 and 180 min after the occlusions. The animals were perfused at the end of the experiment and the heart removed and examined histologically. Tetrazolium salts were reacted with oxidative enzymes to delineate the region of inadequate perfusion. The mean blood pressure and pulse pressure of the SHAM, MCAO/CCAO and CCAO groups significantly declined from initial values (from an average of 78 to 53 mm Hg) during the course of the experiment. However, the mean blood pressure and pulse pressure of the MCAO rats did not change during the experiment, so that the final mean blood pressure and pulse pressure were significantly higher than in the other 3 groups. The levels of both NE and E increased significantly (NE, 1443 +/- 285.9 to 4095 +/- 929 pg/ml; E, 2402 +/- 623 to 3741 +/- 1166 pg/ml) following occlusion in the MCAO group only while the other 3 groups did not change. Four of 6 hearts in the MCAO group were abnormal, showing evidence of subendocardial hemorrhage, ischemic damage or subendocardial congestion. MCAO also resulted in a consistent region of the brain with inadequate perfusion including the insular cortex. These autonomic and myocardial changes appear to mimic some of the changes seen clinically in stroke patients and provide the first acute stroke model for studying autonomic dysfunction in the rat.

Effects of a novel calcium antagonist, KB-2796, on neurologic outcome and size of experimental cerebral infarction in rats

Effects of a novel calcium 2+ antagonist, KB-2796, on neurologic outcome and size of infarction were studied in the rat model of focal cerebral ischemia. Neurologic deficits were examined from 1 to 24 hours after occlusion of the middle cerebral artery and size of infarction was measured at 24 hours postocclusion. When KB-2796 (10 mg/kg, IP) was given immediately after, or 1 hour after, middle cerebral artery occlusion, marked improvement in neurologic score was seen 1 to 3 hours postocclusion. When given immediately after middle cerebral artery occlusion, size of infarction was also markedly smaller when compared with the control rat. The present study suggests that the calcium 2+ antagonist KB-2796 has brain-protective effects against ischemia even with its administration after induction of ischemia.

Focal brain ischemia model in rats. An experimental study

Using 74 male rats, anatomical variations of branching of the proximal segment of the middle cerebral artery were studied. In 36 rats (28 Sprague-Dawley rats and eight spontaneously hypertensive rats), the middle cerebral artery and/or its branches were occluded at various sites. Occlusion of the middle cerebral artery at the lateral border of the olfactory tract with or without simultaneous ligation of the ipsilateral common carotid artery rarely caused cerebral infarction in Sprague-Dawley rats. Occlusion of the olfactory branch in addition to the trunk of the middle cerebral artery caused large infarction of the pallium in five of eight Sprague-Dawley rats. Occlusion of the middle cerebral artery at the medial border of the olfactory tract caused infarction in the pallium and/or basal ganglia in five of six rats, and neurologic deficits were severe and persistent. Occlusion of the middle cerebral artery at the lateral border of the olfactory tract in spontaneously hypertensive rats caused large infarction with severe neurologic deficits in all eight animals. Possible factors responsible for such diverse differences and the relative value of each group as an experimental model of focal cerebral ischemia in rats were discussed.

Neuronal changes in fetal cortex transplanted to ischemic adult rat cortex

Fetal cortex from 16- and 17-day-old embryonic rats was transplanted into the parietal cortex of 12 adult rats rendered ischemic by temporary intraluminal occlusion of the middle cerebral artery. Ischemic injury in the host cortex adjacent to all nine surviving transplants was demonstrated with hematoxylin and eosin and cresyl violet strains. Nicotidamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemical studies revealed a normal number of NADPH-d-positive neurons, whereas acetylcholinesterase (AChE) staining revealed many more AChE-positive neurons in the transplants compared to the host parietal cortex. This could be due to: 1) selective survival of AChE neurons in the transplants compared to the host cortex; 2) increased expression of AChE in transplanted neurons; 3) induction of AChE in normally AChE-negative neurons; or 4) decreased transport of the AChE enzyme from the perikarya to fibers in surviving transplanted neurons. Many fibers positive for AChE and NADPH-d crossed between the host and transplant, although fiber density in the transplants was less than in normal host cortex. These results should encourage future investigation of whether similar transplants improve neurological function following experimental stroke.

The quantification of cerebral infarction following focal ischemia in the rat: influence of strain, arterial pressure, blood glucose concentration, and age

Focal cerebral ischemia was induced by occlusion of the middle cerebral artery in rats. The volumetric assessment of infarcted tissue, 2 days following occlusion, was calculated from the examination of eight preselected coronal sections. Five differing rat strains were examined. A small and variable infarcted volume was seen in Wistar-Kyoto rats; Sprague-Dawley rats had a relatively large, but still variable, infarcted volume. Of the normotensive rat strains, the most reproducible volume of infarcted tissue was seen in Fischer-344 rats; also the absolute value of the infarcted volume did not vary from one series to another in this strain. Chronic arterial hypertension, studied in both normal and stroke-prone spontaneously hypertensive rats, was associated with significantly larger infarction volumes. Age does not change the volume of necrosis: Fischer-344 rats were studied at 3, 9, and 20 months of age, and no significant differences were noted between these ages. Experimental diabetes was induced by the administration of streptozotocin 3 days prior to middle cerebral artery occlusion. Severe hyperglycemia (greater than 400 mg/dl) was associated with a considerably increased volume of infarction. The variability of the resultant lesion is high in the most commonly studied strains, but our results suggest that, for studies in normotensive rats, the use of the Fischer-344 strain produces a standardized and repeatable infarction that may be significantly modified by experimental interventions. Age is not a factor that affects the occlusion-induced infarction; in contrast, both chronic arterial hypertension and experimental diabetes aggravate the histological consequences of middle cerebral artery occlusion in the rat. We conclude that quantitative histological evaluation of infarct size allows a meaningful assessment of the gravity of focal cerebral ischemia.

Focal brain ischemia in the rat: methods for reproducible neocortical infarction using tandem occlusion of the distal middle cerebral and ipsilateral common carotid arteries

This article describes a 3-year experience with focal neocortical ischemia in three rat strains. Multiple groups of adult Wistar (n = 50), Fisher 344 (n = 31), and spontaneously hypertensive (n = 72) rats were subjected to permanent occlusion of the distal middle cerebral (MCA) and ipsilateral common carotid arteries (CCA). Twenty-four hours later the animals were killed, and frozen brain sections were stained with hematoxylin and eosin to demarcate infarcted tissue. The infarct volume for each section was quantified with an image analyzer, and the total infarct volume was calculated with an iterative program that summed all interval volumes. Neocortical infarct volume was the largest and most reproducible in the spontaneously hypertensive rats (SHR). Statistical power analysis to project the numbers of animals necessary to detect a 25 or 50% change in infarct volume with alpha = 0.05 and beta = 0.2 revealed that only the SHR model was practical in terms of requisite animals: i.e., less than 10 animals per group. Tandem occlusion of the distal MCA and ipsilateral CCA in the SHR strain provides a surgically simple method for causing large neocortical infarcts with reproducible topography and volume. The interanimal variability in infarct volume that occurs even in the SHR strain dictates that randomized, concomitant controls are necessary in each study to ensure the accurate assessment of experimental manipulations or pharmacologic therapies.

Photothrombotic occlusion of rat middle cerebral artery: histopathological and hemodynamic sequelae of acute recanalization

The histopathological and hemodynamic consequences of photochemically induced middle cerebral artery (MCA) thrombosis and recanalization were studied in the rat. Recanalization of the thrombosed MCA segment was achieved by the topical application of nimodipine at 1 h following photochemically induced occlusion. Pathological consequences of permanent and temporary occlusion were compared by morphometric procedures 7 days following thrombus formation. Rats with permanent thrombosis exhibited consistent infarction of both striatum and cortex. MCA recanalization at 1 h was associated with a significant reduction in total infarct volume. In recanalized rats, small cortical infarcts, confined to the peripheral MCA territory, were observed in only three of six rats. In contrast, a mixed pattern of infarction and ischemic cell damage was documented throughout the striatum in all rats. Local CBF (1CBF), measured autoradiographically, was significantly reduced in the MCA territory following 1 h of MCA occlusion, especially within the striatum. At 1 h after recanalization, 1CBF recovered within the previously ischemic brain regions to greater than 50% of control. Perfusion deficits were detected by carbon black infusion within focal areas of the striatum following reperfusion. Thus, cortical neurons appear to tolerate 1 h of MCA occlusion in this model. In contrast, reperfusion following 1 h of photochemically induced MCA occlusion gives rise to selective injury to the striatum.

Differential uptake of 3H-thymidine by structures of the pia-arachnoid and cerebral cortex distal to the interrupted middle cerebral artery

Tritiated thymidine accumulated in pial surface structures 1-10 days after interruption of the right middle cerebral artery (MCA) in the rat. Essentially no radioactive marker was present in the underlying cortical territory of the interrupted MCA other than at the operation site. Control meninges, cortex contralateral to the operated MCA, and structures proximal to the operation site were without appreciable accumulation of 3H-thymidine. Thus, the marked cellular proliferative response to MCA interruption was localized to structures of the pia-arachnoid overlying the cortical territory of the interrupted MCA. The data suggest that after MCA occlusion a cellular proliferative response contributes to the expansion of preexisting pial surface collateral vessels and that the expansion does not extend into the parenchyma.

Dorsal cerebral collaterals of stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar Kyoto rats (WKY)

Earlier studies established that stroke-prone spontaneously hypertensive rats (SHRSP) invariably infarct after middle cerebral artery (MCA) occlusion. Normotensive rats are usually protected from infarction after the occlusion. Objectives of this study were to characterize the anastomosing collaterals that may determine the different outcomes to MCA occlusion in SHRSP and Wistar Kyoto rats (WKY). Young (5-10 week) and old (40-69 week) rats of each sex were anesthetized, then administered papaverine to produce maximal vasodilatation of the cerebrovascular bed. Under control conditions latex was injected into the arterial tree to measure the internal diameter of branches of the anterior cerebral artery (ACA), the MCA, and the ACA-MCA anastomosing collaterals. Large diameter ACA and MCA rami in old, but not young, SHRSP were significantly smaller in diameter than the respective ACA and MCA branches in old WKY. The number of ACA-MCA anastomoses was the same for SHRSP and WKY. Mean internal diameter of the ACA-MCA anastomoses was significantly (p less than 0.0001) smaller in SHRSP than WKY in both age groups. There were significant negative correlations between age and 1) the internal diameter of the ACA-MCA anastomoses in WKY but not SHRSP, and 2) the largest diameter ACA and MCA rami in SHRSP but not WKY. The findings suggest that vascular resistance of fully relaxed collaterals is greater in SHRSP than WKY, thereby compromising the dorsal collateral circulation before large diameter vessel changes occur that accompany the established form of hypertension.

Selective gene expression in focal cerebral ischemia

Regional patterns of protein synthesis were examined in rat cortex made ischemic by the occlusion of the right common carotid and middle cerebral arteries. At 2 h of ischemia, proteins were pulse labeled with intracortical injections of a mixture of [3H]leucine, [3H]isoleucine, and [3H]proline. Newly synthesized proteins were analyzed by two-dimensional gel fluorography, and the results correlated with local CBF, measured with [14C]iodoantipyrine as tracer. Small blood flow reductions (CBF = 50-80 ml 100 g-1 min-1) were accompanied by a modest inhibition in synthesis of many proteins and a marked increase in one protein (Mr 27,000). With further reduction in blood flow (CBF = 40 ml 100 g-1 min-1), synthesis became limited to a small group of proteins (Mr 27,000, 34,000, 73,000, 79,000, and actin) including two new polypeptides (Mr 55,000 and 70,000). Severe ischemia (CBF = 15-25 ml 100 g-1 min-1) caused the isoelectric modification of several proteins (Mr 44,000, 55,000, and 70,000) and induced synthesis of another protein (Mr 40,000). Two polypeptides (Mr 27,000 and 70,000) dominated residual protein synthesis in severe ischemia. The changes in protein synthesis induced by different grades of ischemia most likely comprise a variation of the so-called "heat shock" or "stress" response found in all eukaryotic cells subjected to adverse conditions. Since heat shock genes are known to confer partial protection against anoxia and a variety of other noxious insults, their induction may be a factor in limiting the extent of ischemic tissue damage.

Pure cortical ischemia versus striatal ischemia. Circulatory, metabolic, and neuropathologic consequences

Selective ischemic damage was produced either involving only the cortex or together with the striatum by occlusion of the middle cerebral artery proximal or distal to the lenticulostriate artery in the rat. The consequences in local cerebral blood flow, local cerebral glucose utilization, and neuropathology were investigated in the acute stage of ischemia. Caudate damage produced by proximal occlusion resulted in such secondary alterations as enhanced blood flow and metabolism in areas remote from the main lesion, such as in the globus pallidus and substantia nigra ipsilateral to occlusion. After distal occlusion, however, there were two patterns distinctly different from each other in the appearance of the autoradiograms. One was ipsilateral and the other was contralateral enhancement of blood flow and metabolism involving the striato-pallido-nigral axis without any striatal damage. We therefore suggest that these secondary alterations in circulation and metabolism contribute to a varied neurological dysfunction after focal cerebral ischemia. Furthermore, our currently introduced model of selective ischemic lesioning is important in studying the roles of cortical and striatal influences in ischemic pathophysiology.

Interruption of the middle cerebral artery in 10-day-old rat alters normal development of distal collaterals

Pial surface arterioles join rami of the anterior and middle cerebral arteries (MCA) in 10-day-old normal Wistar rats. Normally, the anastomosing branches differentiate into small-diameter vessels with significantly greater tortuosity (length) by 56 days of age. After interruption of th e MCA in 10-day-old rats, large-diameter, relatively straight collaterals were observed 46 or 90-110 days later. Evidently altered hemodynamic factors, as the result of MCA interruption, prevent the development of a normal pattern of arterioles and augment the development of an anomalous pattern of collaterals in young Wistar rats.

Freeze-fracture replica study of capillary endothelium after embolization in the dog

The underlying mechanisms that lead to brain edema following ischemic insult have been subject to much debate. In this study, experimental cerebral infarction was produced in 25 dogs by injecting 1 or 2 silicone rubber cylinders through the cervical internal carotid artery. The animals were sacrificed 24 hours after embolization. Freeze-fracture studies were conducted on the plasma membrane of the capillary endothelium from 15 control and 25 ischemic dogs. No definite findings of tight junction opening were made in the ischemic preparations. Pinocytotic vesicles were seen as concave areas on the protoplasmic face (PF) of the plasma membrane and as protrusions on the extracellular face (EF). The average pinocytotic vesicle count per square micron was increased in ischemic animals. On the luminal side, it reached 22.0 +/- 1.2/sq mu in the 50 PF samples and 29.5 +/- 1.3/sq mu in the 50 EF samples in the experimental preparations, as compared to 7.2 +/- 0.5 sq mu in the 50 PF samples and 9.0 +/- 0.6 sq mu in the 50 EF samples in normal cortex. The average area of the vesicles was also enlarged in experimental animals: 4990.7 +/- 798 sq nm in the 50 PF samples and 4762.8 +/- 878 sq nm in the 50 EF samples, as compared to 3567.7 +/- 570 sq nm in the 50 PF samples and 3404.5 +/- 573 sq nm in the 50 EF samples in normal cortex (p greater than 0.01). These results indicate that transcellular transportation by pinocytotic vesicles plays an important role in the increase of capillary permeability observed in an ischemic model.

Bicuculline methiodide in the blood-brain barrier-epileptogen model of epilepsy

Focal epilepsy can be produced by a blood-brain barrier (BBB)-excluded systemic convulsant (penicillin, folic acid, etc.) in the presence of a focal BBB lesion. Bicuculline methiodide, a gamma-aminobutyric acid blocking epileptogen, crosses the normal BBB of rats poorly and produces no consistent abnormality behaviorally or on EEG at 36 mg/kg. When the BBB is opened in 0.25 ml of cortex by 6,000 rad of alpha particles, by a pin trauma lesion, or by a heat lesion, the rats are normal clinically and on EEG. When these lesioned rats are challenged with bicuculline methiodide, 36 mg/kg, an intense, highly localized epileptiform discharge results that begins approximately 20 min after injection and lasts 30-90 min. The plausibility and experimental utility of the BBB-epileptogen model of epilepsy are enhanced by these observations.

Diameter and length changes in cerebral collaterals after middle cerebral artery occlusion in the young rat

Rapid occlusion of the middle cerebral artery (MCA) in the 36-day-old normal Wistar rat results in change of the dorsal collaterals joining branches of the anterior and middle cerebral arteries. As compared to similarly positioned vessels on the opposite hemisphere and arterioles in unoperated rats of 56 days of age, there were significantly (P less than 0.001) more large (60-120 microM) diameter collaterals on the occluded side 20 days after MCA occlusion. There were fewer small (0-59 microm) diameter collaterals on the occluded side as compared to unoperated rats. The data suggest small diameter arterioles existing at occlusion became large diameter collaterals. The mean number of collaterals per hemisphere was not significantly different (P greater than 0.05) between occluded and unoperated rats. There was no evidence that new vessels were added during the 20-day ligation period. The mean collateral tortuosity value was significantly (P less than 0.01) greater for large diameter vessels on the right occluded side as compared to vessels on the left hemisphere or vessels in unoperated age-matched control rats. The greater tortuosity values of vessels on the occluded side were evidence that collateral vessel length was increased by 24-29% after MCA occlusion. Speculation was made about possible mechanisms responsible for these vascular changes.