Tirilazad reduces cortical infarction after transient but not permanent focal cerebral ischemia in rats.

BACKGROUND AND PURPOSE: We examined the cytoprotective effect of the lipid peroxidation inhibitor tirilazad mesylate (U74006F) in rodent models of neocortical infarction induced by transient and permanent focal cerebral ischemia. METHODS: Wistar rats (experiment 1) and spontaneously hypertensive rats (experiment 2) were subjected to 2 hours of transient middle cerebral artery occlusion followed by 22 hours of reperfusion and pretreated with 10 mg/kg i.p. tirilazad, vehicle, or saline. Repeat doses were given at 4 and 10 hours after reperfusion. Spontaneously hypertensive rats were also subjected to permanent middle cerebral artery occlusion and either pretreated with tirilazad, vehicle, or saline intraperitoneally (experiment 3) or treated with either tirilazad or vehicle intravenously after ischemia (experiment 4). Cortical infarct volumes were measured 24 hours after the onset of either transient or permanent ischemia, and changes in core regional cerebral blood flow were monitored with laser Doppler flowmetry. RESULTS: Tirilazad reduced infarct volume after transient ischemia by 40% in Wistar rats (p = 0.08) (experiment 1) and 23% in spontaneously hypertensive rats (p less than 0.05) (experiment 2) but did not reduce infarction after permanent ischemia whether it was given intraperitoneally (experiment 3) or intravenously (experiment 4). Ischemic core blood flows were not affected during ischemia, nor were they affected during reperfusion after transient ischemia. CONCLUSIONS: Tirilazad reduces cortical infarction in transient but not permanent ischemia, an effect not related to improvement in regional cerebral blood flow. Tirilazad might prove to be useful as an adjuvant therapy after successful thrombolysis in acute stroke patients.     

Temporal thresholds for neocortical infarction in rats subjected to reversible focal cerebral ischemia.

We investigated the temporal threshold for focal cerebral infarction in the spontaneously hypertensive rat. The right middle cerebral artery and common carotid artery were occluded for 0, 1, 2, 3, 4, or 24 hours, and all the animals were sacrificed 24 hours after the onset of ischemia. Cortical infarct volumes and edema volumes were quantified in serial frozen sections of hematoxylin and eosin-stained tissue using image analysis. Upon occlusion, blood flow in the core of the ischemic zone, measured with laser-Doppler flowmetry, fell to a mean +/- standard deviation of 21 +/- 7% of the preocclusion baseline value (n = 26). During the first hour of ischemia, blood flow in the densely ischemic zone rose to 27 +/- 8% of baseline (n = 25). Release of the middle cerebral artery and common carotid artery occlusions rapidly restored cortical blood flow to 213 +/- 83% of baseline (n = 21). Focal ischemia of 1 hour's duration caused little or no infarction, while ischemic intervals of 2 and 3 hours produced successively larger volumes of infarcted cortex. Ischemic intervals of 3-4 hours' duration followed by approximately 20 hours of recirculation yielded infarct volumes that were not significantly different from those after 24 hours of permanent focal ischemia. The results indicate that 3-4 hours of focal cerebral ischemia in this rat model is sufficient to attain maximal infarction and suggest that recirculation or pharmacological interventions after this time will provide little benefit.     

Delayed AMPA receptor blockade reduces cerebral infarction induced by focal ischemia.

The potent and selective AMPA receptor antagonist NBQX was tested for cytoprotective properties in an adult rat model of transient focal neocortical ischemia. Nineteen spontaneously hypertensive rats sustained 2 h of middle cerebral artery occlusion, followed by 22 h of recirculation. Ninety minutes following the onset of ischemia, at the time of, and 30 min following reperfusion, they received i.p. injections of either saline (n = 10) or 30 mg kg-1 of NBQX (n = 9). Saline-treated rats had a mean volume of neocortical infarction ( +/- s.d.) of 181 +/- 31 mm3, while NBQX-treated rats sustained significantly less damage, 125 +/- 19 mm3 (p less than 0.001). Regional cerebral blood flows during ischemia and reperfusion were not affected by the drug. We suggest that the AMPA receptor may play an important role in ischemic cerebral infarction.     

The effect of the NMDA receptor antagonist MK-801 on cerebral blood flow and infarct volume in experimental focal stroke

The non-competitive N-methyl-D-aspartate receptor/channel antagonist dizocilipine maleate (MK-801) has been reported to reduce infarct volume in a variety of focal stroke models. We examined the effect of MK-801 on infarct volume and cerebral blood flow in temporary and permanent focal ischemia in rats. In Wistar rats exposed to permanent right common carotid artery and 2 h of transient right middle cerebral and left common carotid artery occlusion followed by 22 h of reperfusion, MK-801 reduced infarct volume by 73% (P less than 0.05) and significantly increased cerebral blood flow to the ischemic core throughout the 2-h period of ischemia. In spontaneously hypertensive rats (SHRs) exposed to permanent right common carotid artery occlusion and 2 h of transient right middle cerebral artery occlusion followed by 22 h of reperfusion, MK-801 decreased infarct volume by 13% (P greater than 0.05) and increased cerebral blood flow to the penumbral region. In SHRs subjected to permanent right common carotid and middle cerebral artery occlusion MK-801 reduced infarct volume by 18% at 3 h (P greater than 0.05), by 25% at 6 h (P less than 0.01) and by 18% at 24 h (P less than 0.05). MK-801-treated SHRs had no difference in cerebral blood flow to the ischemic core, but increased cerebral blood flow to penumbral zones as compared with untreated SHRs. These results suggest that the protective effect of MK-801, at least in part, relates to improved cerebral blood flow.     

CBF changes associated with focal ischemic preconditioning in the spontaneously hypertensive rat.

Experimental stroke models exhibit robust protection after prior preconditioning (PC) insults. This study comprehensively examined cerebral blood flow (CBF) responses to permanent middle cerebral artery (MCA) occlusion in spontaneously hypertensive rats preconditioned by noninjurious transient focal ischemia, using [(14)C]iodoantipyrine autoradiography at varied occlusion intervals. Preconditioning was produced by 10-min occlusion of the MCA and ipsilateral common carotid artery under halothane anesthesia. These vessels were permanently coagulated 24 h later in na?ve, PC, and sham-operated rats. Infarct volumes were determined from hematoxylin-eosin-stained frozen sections after 1 or 3 days. Edema-corrected infarct volume was reduced from 127+/-21 in na?ve rats to 101+/-31 and 52+/-28 mm(3) in sham and PC groups, respectively, at 1 day, with similar results at 3 days. All animals exhibited a consistent CBF threshold for infarction (approximately 30 mL/100 g/min). Tissue volumes below this threshold were identical in na?ve and PC groups after 15-min occlusion. However, by 3 h the volume of ischemic cortex decreased in the PC group but remained unchanged in na?ve rats, predicting final infarct volumes. Cerebral blood flow recovery was confirmed in brains of individual rats evaluated by repeated laser Doppler perfusion imaging during the same 3-h interval. Modest sham protection correlated with better-maintained global perfusion, detectable also in the contralateral cortex, apparently reflecting the PC effects of prior anesthesia. These results establish that timely reperfusion of penumbra, achieved by synergistic mechanisms, is a primary determinant of PC-induced protection in experimental stroke.     

高血压大鼠局部脑缺血再灌流边缘区超微结构改变

用透射电镜观察了肾血管性高血压大鼠局部脑缺血早期再灌流及持续缺血９个实验组和假手术组缺血边缘区超微结构改变。结果发现：局部脑缺血０．５至３小时再灌流均较相应持续缺血神经元损害轻；缺血６小时再灌流，神经元细胞器固缩，并有暗黑颗粒沉积。表明在高血压鼠局部脑缺血早期，恢复血流有利于边缘区神经元恢复。     

Immediate or delayed mild hypothermia prevents focal cerebral infarction

The protective effect of mild hypothermia was studied in rodent models of both permanent and transient focal cerebral ischemia. In Expt. 1, Wistar rats were exposed to 6 h permanent ischemia by bilateral occlusion of both common carotid arteries and right middle cerebral artery. In Expt. 2, animals were exposed to 3 h transient ischemia followed by 21 h reperfusion, and in Expt. 3, 3 h transient ischemia was followed by 69 h of reperfusion. Expt. 4 used 3 h transient ischemia followed by 3 h reperfusion. In Expt. 1, animals maintained at 37 degrees C rectal (normothermia) suffered a mean infarct volume (+/- S.D.) of 142 +/- 44 mm3 (n = 6), which was reduced for those exposed to permanent hypothermic (32 degrees C) ischemia to 56 +/- 64 mm3 (n = 10) (P less than 0.05). In Expt. 2, normothermic ischemia and reperfusion resulted in an infarction of 211 +/- 35 mm3 (n = 6). Intra-ischemic hypothermia (32 degrees C) followed by 21 h of normothermic reperfusion resulted in 17 +/- 12 mm3 of infarction (n = 9) (P less than 0.001). Hypothermia for either the first or second 1.5 h of the 3 h ischemic insult reduced the infarct volume to 116 +/- 76 mm3 (n = 6) (P less than 0.05) or 108 +/- 73 mm3 (n = 7) (P less than 0.01), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reduction of tissue plasminogen activator-induced hemorrhage and brain injury by free radical spin trapping after embolic focal cerebral ischemia in rats.

Thrombolytic stroke therapy with tissue plasminogen activator (tPA) remains complicated by serious risks of cerebral hemorrhage and brain injury. In this study, a novel model of tPA-induced hemorrhage was used in spontaneously hypertensive rats to examine the correlates of hemorrhage, and test methods of reducing hemorrhage and brain injury. Homologous blood clot emboli were used to occlude the middle cerebral artery in spontaneously hypertensive rats, and delayed administration of tPA (6 hours postischemia) resulted in high rates of cerebral hemorrhage 24 hours later. Compared with untreated rats, tPA significantly increased hemorrhage volumes by almost 85%. Concomitantly, infarction and neurological deficits were worsened by tPA. A parallel experiment in normotensive Wistar-Kyoto rats showed markedly reduced rates of hemorrhage, and tPA did not significantly increase hemorrhage volumes. To examine whether tPA-induced hemorrhage was caused by the delayed onset of reperfusion per se, another group of spontaneously hypertensive rats was subjected to focal ischemia using a mechanical method of arterial occlusion. Delayed (6 hours) reperfusion via mechanical means did not induce hemorrhage. However, administration of tPA plus delayed mechanical reperfusion significantly increased hemorrhage volumes. Since reperfusion injury was implicated, a final experiment compared outcomes in spontaneously hypertensive rats treated with tPA plus the free radical spin trap alpha-phenyl tert butyl nitrone (alpha-PBN) versus tPA alone. tPA-induced hemorrhage volumes were reduced by 40% with alpha-PBN, and infarction and neurological deficits were also decreased. These results indicate that (1) blood pressure is an important correlate of tPA-induced hemorrhage, (2) tPA interacts negatively with reperfusion injury to promote hemorrhage, and (3) combination therapies with anti-free radical treatments may reduce the severity of tPA-induced hemorrhage and brain injury after cerebral ischemia.     

人工合成E-选择素治疗大鼠局灶脑缺血再灌注损伤的探讨

目的：探讨新的药物治疗脑缺血再灌注损伤。方法：用人工合成 Ｅ－选择素 ２ｍｇ·ｋｇ－１或 １０ ｍｇ·ｋｇ－１溶解于生理盐水中,静脉注入自发性高血压大鼠永久左侧大脑中动脉／颈总动脉（ＭＣＡ／ＣＣＡ）闭塞或ＭＣＡ／ＣＣＡ闭塞２ｈ后ＣＣＡ再灌注模型中。２４ｈ后,脑梗死体积用计算机扫描计算。结果：在永久性ＭＣＡ／ＣＣＡ闭死组中脑梗死体积没有差别,在ＭＣＡ／ＣＣＡ闭死后ＣＣＡ再灌注组中脑梗死体积有意义地缩小（Ｐ＜０．０１）。结论：Ｅ－选择素能够有效地减少大鼠脑缺血再灌注损伤。     

Reperfusion increases neutrophils and leukotriene B4 receptor binding in rat focal ischemia.

BACKGROUND AND PURPOSE: Neutrophils are critically involved with ischemia and reperfusion injury in many tissues but have not been studied under conditions of reperfusion after focal cerebral ischemia. The present studies were conducted to confirm our previous observations quantifying neutrophils in rat permanent focal stroke using a myeloperoxidase activity assay and to extend them to transient ischemia with reperfusion. In addition, leukotriene B4 receptor binding in ischemic tissue was evaluated as a potential marker for inflammatory cell infiltration. METHODS: Histological, enzymatic, and receptor binding techniques were used to evaluate neutrophil infiltration and receptor binding in infarcted cortical tissue 24 hours after permanent middle cerebral artery occlusion (n = 25) or temporary occlusion for 80 (n = 12) or 160 (n = 22) minutes followed by reperfusion for 24 hours in spontaneously hypertensive rats. RESULTS: Sham surgery (n = 26) produced no changes in any parameter measured. After permanent middle cerebral artery occlusion, neutrophil accumulation was observed histologically, but the infiltration was moderate and typically within and adjacent to blood vessels bordering the infarcted cortex. After temporary middle cerebral artery occlusion with reperfusion, marked neutrophil infiltration was observed throughout the infarcted cortex. Myeloperoxidase activity was increased (p less than 0.05) after permanent occlusion and to a greater extent after temporary occlusion with reperfusion. Myeloperoxidase activity (units per gram wet weight) in ischemic cortex was increased over that in nonischemic (control) cortex 32.2-fold, 54.6-fold, and 92.1-fold for permanent occlusion and 80 and 160 minutes of temporary occlusion with reperfusion, respectively (p less than 0.05). Sham surgery produced no changes in myeloperoxidase activity. Leukotriene B4 receptor binding also was increased (p less than 0.05) after focal ischemia and paralleled the increases in myeloperoxidase activity. Ischemic cortex-specific receptor binding (femtomoles per milligram protein) was 3.87 +/- 0.63 in sham-operated rats and 4.57 +/- 0.98, 8.98 +/- 1.11, and 11.12 +/- 1.63 for rats subjected to permanent occlusion and 80 and 160 minutes of temporary occlusion with reperfusion, respectively (all p less than 0.05 different from sham-operated). Cortical myeloperoxidase activity was significantly correlated with the degree of cortical leukotriene B4 receptor binding (r = 0.66 and r = 0.79 in two different studies, p less than 0.01). CONCLUSION: These data indicate that neutrophils are involved in focal ischemia and that there is a dramatic accumulation of neutrophils in infarcted tissue during reperfusion that can be quantified using the myeloperoxidase activity assay. Leukotriene B4 receptor binding increases in infarcted tissue in a parallel manner, which suggests that the increased leukotriene B4 binding is to receptors located on the accumulating neutrophils.     

Selective blockade of N-type voltage-sensitive calcium channels protects against brain injury after transient focal cerebral ischemia in rats

The neuroprotective efficacy of the selective N-type voltage-sensitive calcium channel blocker, SNX-111, was evaluated in spontaneously hypertensive rats subjected to 60 min of focal cerebral ischemia by permanent ligation of the right common carotid artery and temporary occlusion of the right middle cerebral artery. Intravenous infusion of 167 μg/kg per min SNX-111 for 30 min (5 mg/kg), initiated immediately after reperfusion, significantly reduced cortical infarct volumes measured 24 h after the ischemic insult.     

Hypothermic protection in rat focal ischemia models: strain differences and relevance to "reperfusion injury".

Hypothermic protection was compared in Long-Evans and spontaneously hypertensive rat (SHR) strains using transient focal ischemia, and in Wistar and SHR strains using permanent focal ischemia. Focal ischemia was produced by distal surgical occlusion of the middle cerebral artery and tandem occlusion of the ipsilateral common carotid artery (MCA/CCAO). Moderate hypothermia of 2 hours' duration was produced by systemic cooling to 32 degrees C, with further cooling of the brain achieved by reducing to 30 degrees C the temperature of the saline drip superfusing the exposed occlusion site. Infarct volume was determined from serial hematoxylin and eosin-stained frozen sections obtained routinely at 24 hours, or in some cases after 3 days' survival. In the SHR, moderate hypothermia was only effective when initiated before recirculation after a 90-minute occlusion period. In contrast, the same intervention was strikingly effective in the Long-Evans rat even when initiated after as long as 30-minute reperfusion after a 3-hour occlusion. This magnitude and duration of cooling was not protective in permanent MCA/CCAO in the SHR, but such transient hypothermia did effectively reduce infarct volume after permanent occlusions in Wistar rats. These results show striking differences in the temporal window for hypothermic protection among rat focal ischemia models. As expected, "reperfusion injury" in the Long-Evans strain is particularly responsive to delayed cooling. The finding that the SHR can be protected by hypothermia initiated immediately before recirculation suggests a rapidly evolving component of injury occurs subsequent to reperfusion in this model as well. Hypothermic protection after permanent occlusion in Wistar rats identifies a transient, temperature-sensitive phase of infarct evolution that is not evident in the unreperfused SHR. These observations confirm that distinct mechanisms can underlie the temporal progression of injury in rat stroke models, and emphasize the critical importance of considering model and strain differences in extrapolating results of hypothermic protection studies in animals to the design of interventions in clinical stroke.     

Cortical spreading depression causes a long-lasting decrease in cerebral blood flow and induces tolerance to permanent focal ischemia in rat brain.

Cortical spreading depression (CSD) has previously been shown to induce tolerance to a subsequent episode of transient cerebral ischemia. The objective of the present study was to determine whether CSD also induces tolerance to permanent focal ischemia and, if so, whether tolerance may be mediated by alterations in cerebral blood flow (CBF). Sprague-Dawley rats were preconditioned by applying potassium chloride to one hemisphere for 2 hours, evoking 19 +/- 5 episodes of CSD (mean +/- SD, n = 19). Three days later, the middle cerebral artery (MCA) was permanently occluded using an intraluminal suture. In a subset of animals, laser Doppler blood flow (LDF) was monitored over the parietal cortex before and during the first 2 hours of MCA occlusion. Preconditioning with CSD reduced the hemispheric volume of infarction from 248 +/- 115 mm3 (n = 18) in sham-conditioned animals to 161 +/- 81 mm3 (n = 19, P< 0.02). Similarly, CSD reduced the neocortical volume of infarction from 126 +/- 82 mm3 to 60 +/- 61 mm3 (P < 0.01). Moreover, preconditioning with CSD significantly improved LDF during MCA occlusion from 21% +/- 7% (n = 9) of preischemic baseline in sham-conditioned animals to 29% +/- 9% (n = 7, P< 0.02). Preconditioning with CSD therefore preserved relative levels of CBF during focal ischemia and reduced the extent of infarction resulting from permanent MCA occlusion. To determine whether CSD may have altered preischemic baseline CBF, [14 C]iodoantipyrine was used in additional animals to measure CBF 3 days after CSD conditioning or sham conditioning. CSD, but not sham conditioning, significantly reduced baseline CBF in the ipsilateral neocortex to values 67% to 75% of those in the contralateral cortex. Therefore, CSD causes a long-lasting decrease in baseline CBF that is most likely related to a reduction in metabolic rate. A reduction in the rate of metabolism may contribute to the induction of tolerance to ischemia after preconditioning with CSD.     

Effect of allopurinol on ischemia and reperfusion-induced cerebral injury in spontaneously hypertensive rats

In spontaneously hypertensive rats, we studied the participation of xanthine oxidase-linked free radical in ischemia and reperfusion-induced cerebral injury, using allopurinol, a xanthine oxidase inhibitor. The loss of righting reflex was noted in some animals after a 4 hour occlusion of bilateral common carotid arteries and 19 of 25 animals died within 72 hours after reperfusion. One hour after reperfusion, the cerebral water content increased significantly, with an increase in sodium content and a decrease in potassium content. In 7 animals treated with oral administrations of allopurinol (200 mg/kg) 24 hours and 1 hour before occlusion, no death was found either during occlusion or after reperfusion, and the loss of righting reflex was noted in only one animal 24-72 hours following reperfusion. The increase in cerebral water content and accompanied changes in electrolyte contents were clearly prevented by allopurinol. These results suggest the possibility that the production of xanthine oxidase-linked free radical participates in cerebral injury due to ischemia and reperfusion in spontaneously hypertensive rats.     

Penumbral tissues salvaged by reperfusion following middle cerebral artery occlusion in rats.

BACKGROUND AND PURPOSE: The rat is now extensively used for studies on focal cerebral ischemia, and several novel pharmacological principles have been worked out in rat models of middle cerebral artery occlusion. The objective of the present study was to assess how ischemic tissue can be salvaged by reperfusion in a model of transient focal ischemia that gives infarction of both the caudoputamen and the neocortex. METHODS: The middle cerebral artery of anesthetized rats was occluded for 15, 30, 60, 90, 120, or 180 minutes by an intraluminal filament, and recirculation was instituted for 7 days to allow assessment of the density and localization of ischemic brain damage using histopathologic techniques. Local cerebral blood flow was measured in separate animals to verify that removal of the filament was followed by adequate recirculation. RESULTS: Following 15 minutes of middle cerebral artery occlusion seven of eight rats showed selective neuronal necrosis in the caudoputamen, while the neocortex was normal. After 30 minutes of occlusion, seven of eight animals had infarcts localized to the lateral caudoputamen, and four of eight had selective neuronal necrosis in the neocortex. Prolongation of the ischemia to 60 minutes induced cortical infarction in all eight rats. The infarct size increased progressively with increasing occlusion time, up to 120-180 minutes, when the infarcts were as extensive as those observed following 24 hours of permanent middle cerebral artery occlusion. CONCLUSIONS: The results demonstrate a time window for salvage of penumbral tissues by reperfusion that is shorter than that suggested on the basis of previous data in other species. The results probably reflect a lower collateral blood flow in the rat than in other species. This should be taken into account when the effect of pharmacological agents is studied in rats.     

Age-related vulnerability to cerebral ischemia in spontaneously hypertensive rats.

BACKGROUND AND PURPOSE: We sought to determine the effects of aging on regional cerebral blood flow and ischemic brain damage in transient cerebral ischemia in rats. METHODS: Five adult (5-6 months) and five aged (18-22 months) female spontaneously hypertensive rats were subjected to 20 minutes of bilateral carotid occlusion and 60 minutes of recirculation under amobarbital anesthesia (100 mg/kg i.p.). Regional cerebral blood flow in the hippocampus and striatum was measured using the hydrogen clearance method. Nine adult and 14 aged rats were subjected to 20 minutes of bilateral carotid occlusion or were sham-operated under ether anesthesia. Seven days after 20 minutes of cerebral ischemia, the rats' brains were perfusion fixed. Ischemic damage in the hippocampus and striatum was graded (0 [normal] to 3 [majority of neurons damaged]). RESULTS: After 20 minutes of bilateral carotid occlusion, striatal cerebral blood flow decreased to 9.1 +/- 1.5 and 3.9 +/- 2.0 ml/100 g/min in aged and adult rats, respectively, and hippocampal cerebral blood flow decreased to 8.6 +/- 2.4 and 5.7 +/- 2.4 in aged and adult rats, respectively. Although these ischemic cerebral blood flow values were not significantly different between the two age groups, scores for ischemic damage in the hippocampus CA-1 subfield and striatum were significantly higher in aged than in adult rats (p less than 0.05, Kruskal-Wallis' h test with Bonferroni correction). CONCLUSIONS: We conclude that aging may be a primary factor in the development of greater ischemic neuronal damage observed in aged hypertensive rats.     

Correlation between cerebral blood flow and histologic changes in a new rat model of middle cerebral artery occlusion

We describe a new focal ischemia model consisting of unilateral middle cerebral artery occlusion with a silicone rubber cylinder attached to a nylon surgical thread inserted through the internal carotid artery in rats. Recirculation was accomplished by pulling the thread out of the artery. We evaluated the reliability of this model and studied the influence of reperfusion of the brain by measuring regional cerebral blood flow in 30 rats and by using conventional neuropathologic methods after different periods of occlusion in 48 rats. The anterior neocortex and the lateral part of the caudate putamen, which were supplied by the occluded middle cerebral artery, were the regions most frequently damaged. After 1 hour of occlusion in five rats, in the cortex supplied by the occluded artery mean +/- SD blood flow was 0.19 +/- 0.08 ml/g/min (approximately 15% of that in the corresponding region of five sham-operated control rats), and mild scattered ischemic cell change was observed. Three (n = 5) or six (n = 5) hours of occlusion reduced blood flow more severely and caused severe ischemic cell changes in the cortex supplied by the occluded artery in proportion to the duration of ischemia. Characteristically, in five rats subjected to 3 hours of occlusion followed by 3 hours of recirculation, blood flow was restored and spongy edematous change was observed in the cortex supplied by the recirculated artery. This change resulted in hypoperfusion of the neighboring cortical region surrounding the recirculated area. Our model should be useful in various investigations of the influence of reperfusion on focal ischemic brain injury.     

Failure of GM1 ganglioside to influence outcome in experimental focal ischemia.

BACKGROUND AND PURPOSE: Reports of improved short-term (less than 72 hours) outcome in experimental models of mechanical and ischemic central nervous system injury suggest that exogenous ganglioside administration may confer a protective effect on neural tissue. We studied the effect of the monosialoganglioside GM1 on cerebral infarction and edema in spontaneously hypertensive rats subjected to permanent focal cerebral ischemia. METHODS: GM1 or normal saline was injected intramuscularly once a day for 3 days before and 30 and 120 minutes after occlusion of the right middle and common carotid arteries. Following a 24-hour survival period, the volume of infarction was measured by computer-assisted image analysis, and the extent of edema was assessed by measurements of tissue water content and hemispheric volume. RESULTS: Infarct volume was similar among the GM1-treated (n = 10) and saline-treated (n = 10) rats (212 +/- 10 versus 220 +/- 13 microliters, respectively). In a second series of experiments, the brain water content and edema volume of the ischemic right hemisphere in GM1-treated rats (n = 10) did not differ from saline-treated controls (n = 10). CONCLUSIONS: GM1 ganglioside does not effectively reduce cerebral infarction caused by permanent focal ischemia.     

Time course of cerebral blood flow and histological outcome after focal cerebral ischemia in rats.

BACKGROUND AND PURPOSE: The relation between time-dependent changes in cerebral blood flow and the appearance of infarction after focal cerebral ischemia is still a matter for debate. The aim of this study was to measure perfusion after simultaneous occlusions of the left middle cerebral artery and ipsilateral common carotid artery in rats and correlate it with the timing and distribution of histological changes. METHODS: We studied histological and cerebral blood flow changes 5 minutes and 4, 24, and 48 hours after the onset of focal ischemia. Blood flow was determined autoradiographically using [14C]iodoantipyrine. A coronal template subdivided into regions of interest was applied to the autoradiographs and the histological data. RESULTS: In some regions of the nonoccluded hemisphere, cerebral blood flow 5 minutes after occlusion fell below 50% of normal. Many ischemic structures showed stable blood flow for 48 hours after occlusion, confirming that in this model reperfusion is minimal. Infarction occurred eventually in all areas in which blood flow at 5 minutes fell below 10% of that in control rats, but infarction appeared earlier in regions in which blood flow at 5 minutes was below 5% of that in control rats. When blood flow at 5 minutes rose above 12% of that in control rats, the occurrence of infarction became unpredictable. CONCLUSIONS: Despite the general dependence of infarction on perfusion levels, blood flow was not a reliable indicator of those regions committed to infarction.     

Continuous nimodipine treatment attenuates cortical infarction in rats subjected to 24 hours of focal cerebral ischemia

Focal cerebral infarction and edema were measured in rats (Wistar, Fisher 344, and spontaneously hypertensive strains) pretreated with nimodipine (2 micrograms/kg/min i.v.) or its vehicle and subjected to the tandem occlusion of the middle cerebral and common carotid arteries. Animals awoke from anesthesia 10-15 min after onset of ischemia and continued to receive treatment over a 24-h survival period. Cortical infarction and edema were quantified by image analysis of frozen brain sections processed for histology. Nimodipine-treated rats developed 20-60% smaller cortical infarct volumes than controls (p less than 0.002). Cortical edema was reduced proportionately to the decrease in infarct volume and constituted approximately 36% of the infarct volume. Nimodipine caused a mild hypotensive response that did not aggravate ischemic brain damage. The results indicate that continuous nimodipine treatment, started before induction of focal cerebral ischemia, can attenuate ischemic brain damage and edema as late as 24 h after the onset of ischemia.