Onset Of Focal Cerebral Ischemia Research Articles

Sur1-Trpm4 Cation Channel Expression in Human Cerebral Infarcts.

The nonselective monovalent cation channel transient receptor potential melastatin 4 (Trpm4) is transcriptionally upregulated in neural and vascular cells in animal models of brain infarction. It associates with sulfonylurea receptor 1 (Sur1) to form Sur1-Trpm4 channels, which have critical roles in cytotoxic edema, cell death, blood-brain barrier breakdown, and vasogenic edema. We examined Trpm4 expression in postmortem brain specimens from 15 patients who died within the first 31 days of the onset of focal cerebral ischemia. We found increased Trpm4 protein expression in all cases using immunohistochemistry; transcriptional upregulation was confirmed using in situ hybridization of Trpm4 messenger RNA. Transient receptor potential melastatin 4 colocalized and coassociated with Sur1 within ischemic endothelial cells and neurons. Coexpression of Sur1 and Trpm4 in necrotic endothelial cells was also associated with vasogenic edema indicated by upregulated perivascular tumor necrosis factor, extravasation of serum immunoglobulin G, and associated inflammation. Upregulated Trpm4 protein was present up to 1 month after the onset of cerebral ischemia. In a rat model of middle cerebral artery occlusion stroke, pharmacologic channel blockade by glibenclamide, a selective inhibitor of sulfonylurea receptor, mitigated perivascular tumor necrosis factor labeling. Thus, upregulated Sur1-Trpm4 channels and associated blood-brain barrier disruption and cerebral edema suggest that pharmacologic targeting of this channel may represent a promising therapeutic strategy for the clinical management of patients with cerebral ischemia.

Stroke increases neural stem cells and angiogenesis in the neurogenic niche of the adult mouse.

The unique cellular and vascular architecture of the adult ventricular-subventricular zone (V/SVZ) neurogenic niche plays an important role in regulating neural stem cell function. However, the in vivo identification of neural stem cells and their relationship to blood vessels within this niche in response to stroke remain largely unknown. Using whole-mount preparation of the lateral ventricle wall, we examined the architecture of neural stem cells and blood vessels in the V/SVZ of adult mouse over the course of 3 months after onset of focal cerebral ischemia. Stroke substantially increased the number of glial fibrillary acidic protein (GFAP) positive neural stem cells that are in contact with the cerebrospinal fluid (CSF) via their apical processes at the center of pinwheel structures formed by ependymal cells residing in the lateral ventricle. Long basal processes of these cells extended to blood vessels beneath the ependymal layer. Moreover, stroke increased V/SVZ endothelial cell proliferation from 2% in non-ischemic mice to 12 and 15% at 7 and 14 days after stroke, respectively. Vascular volume in the V/SVZ was augmented from 3% of the total volume prior to stroke to 6% at 90 days after stroke. Stroke-increased angiogenesis was closely associated with neuroblasts that expanded to nearly encompass the entire lateral ventricular wall in the V/SVZ. These data indicate that stroke induces long-term alterations of the neural stem cell and vascular architecture of the adult V/SVZ neurogenic niche. These post-stroke structural changes may provide insight into neural stem cell mediation of stroke-induced neurogenesis through the interaction of neural stem cells with proteins in the CSF and their sub-ependymal neurovascular interaction.

A Type-II Positive Allosteric Modulator of α7 nAChRs Reduces Brain Injury and Improves Neurological Function after Focal Cerebral Ischemia in Rats

In the absence of clinically-efficacious therapies for ischemic stroke there is a critical need for development of new therapeutic concepts and approaches for prevention of brain injury secondary to cerebral ischemia. This study tests the hypothesis that administration of PNU-120596, a type-II positive allosteric modulator (PAM-II) of α7 nicotinic acetylcholine receptors (nAChRs), as long as 6 hours after the onset of focal cerebral ischemia significantly reduces brain injury and neurological deficits in an animal model of ischemic stroke. Focal cerebral ischemia was induced by a transient (90 min) middle cerebral artery occlusion (MCAO). Animals were then subdivided into two groups and injected intravenously (i.v.) 6 hours post-MCAO with either 1 mg/kg PNU-120596 (treated group) or vehicle only (untreated group). Measurements of cerebral infarct volumes and neurological behavioral tests were performed 24 hrs post-MCAO. PNU-120596 significantly reduced cerebral infarct volume and improved neurological function as evidenced by the results of Bederson, rolling cylinder and ladder rung walking tests. These results forecast a high therapeutic potential for PAMs-II as effective recruiters and activators of endogenous α7 nAChR-dependent cholinergic pathways to reduce brain injury and improve neurological function after cerebral ischemic stroke.

Intracarotid administration of human bone marrow mononuclear cells in rat photothrombotic ischemia

BackgroundIncreasing evidence suggests that cell therapy improves functional recovery in experimental models of stroke and myocardial infarction. So far only small pilot trials tested the effects of cell therapy in stroke patients, whereas large clinical trials were conducted in patients with ischemic heart disease. To investigate the therapeutic benefit of cell therapy to improve the recovery after stroke, we determined the efficacy of bone marrow derived mononuclear cells, which were shown to improve the recovery in experimental and clinical acute myocardial infarction studies, in a rat stroke model.MethodsAdult male Wistar rats were randomly assigned to receive either five million human bone marrow mononuclear cells (hBMC) or placebo intraarterially 3 days after photothrombotic ischemia. For immunosuppression the animals received daily injections of cyclosporine throughout the experiment, commencing 24 hours before the cell transplantation. A battery of behavioral tests was performed before and up to 4 weeks after ischemia.ResultsBody temperature and body weight revealed no difference between groups. Neurological deficits measured by the Rotarod test, the adhesive-removal test and the cylinder test were not improved by hBMC transplantation compared to placebo.ConclusionsThis study demonstrates that hBMC do not improve functional recovery when transplanted intraaterially 3 days after the onset of focal cerebral ischemia. A possible reason for the failed neurological improvement after cell therapy might be the delayed treatment initiation compared to other experimental stroke studies that showed efficacy of bone marrow mononuclear cells.

Intravenous Thrombolysis in German Stroke Units before and after Regulatory Approval of Recombinant Tissue Plasminogen Activator

Background: Intravenous thrombolysis with recombinant tissue plasminogen activator (rt-PA) within 3 h after onset of focal cerebral ischemia was approved in Germany in August 2000. Methods: 11 neurology departments with acute stroke units participated in the German Stroke Study Collaboration before (n = 2,925) and after (n = 3,204) approval of rt-PA in Germany and consecutively registered all patients admitted within 24 h following acute ischemic stroke. Results: Frequency of intravenous thrombolysis in patients admitted within 24 h after symptom onset increased from 4.8% before approval to 7.9% after approval of rt-PA. Among patients treated with rtPA, age increased significantly and the delay between symptom onset and imaging was significantly shorter in the second study period. Conclusions: The observed improvement in management and quantity of intravenous thrombolysis may be explained by greater experience and greater legal security following regulatory approval of rtPA.

Acute cerebral ischemia in rats studied by Carr-Purcell spin-echo magnetic resonance imaging: assessment of blood oxygenation level-dependent and tissue effects on the transverse relaxation.

Acute cerebral ischemia has been shown to be associated with an enhanced transverse relaxation rate in rat brain parenchyma, chiefly due to the blood oxygenation level-dependent (BOLD) effect. In this study, Carr-Purcell R(2) (CP R(2)), acquired both with short and long time intervals between centers of adiabatic pi-pulses (tau(CP)), was used to assess the contributions of BOLD and tissue effects to the transverse relaxation in two brain ischemia models of rat at 4.7 T. R(1rho) and diffusion MR images were also acquired in the same animals. During the first minutes of global ischemia, the long tau(CP) R(2) in brain parenchyma increased, whereas the short tau(CP) R(2) was unchanged. Based on the simulations, and using constraints of intravascular BOLD effect on parenchymal R(2), the former observation was ascribed to be due to susceptibility changes arising in the extravascular compartment. R(1rho) declined almost immediately after the onset of focal cerebral ischemia, and further declined during the evolution of ischemic damage. Interestingly, short tau(CP) CP R(2) started to decline after some 20 min of focal ischemia and declined over a time course similar to that of R(1rho), indicating that it may be an MRI marker for irreversible tissue changes in cerebral ischemia. The present results show that CP R(2) MRI can reveal both tissue- and blood-derived contrast changes in acute cerebral ischemia.

Effects of nonpeptide V(1) vasopressin receptor antagonist SR-49059 on infarction volume and recovery of function in a focal embolic stroke model.

Cerebral edema develops very early after the onset of focal cerebral ischemia and may be a major factor in early disability after an acute ischemic stroke. There have been very limited studies on the usefulness of antiedemic agents as neuroprotective agents in the setting of focal cerebral ischemia. We tested the neuroprotective effects of a new potent nonpeptide vasopressin receptor V(1) antagonist, SR-49059, in a focal embolic stroke model in rats. Focal ischemic injury was induced by embolizing a preformed clot into the middle cerebral artery (MCA). Infarction volume was measured at 48 hours after the MCA occlusion. Neurological deficits, ischemic brain edema, seizure activity, and mortality and hemorrhage rates were also documented. Treatment with SR-49059 (2 mg/kg), initiated immediately after MCA occlusion, significantly reduced infarction volume (P<0.05) measured at 48 hours after the arterial occlusion. In animals in which the treatment was delayed for 1 hour after MCA occlusion, infarction volume was also reduced significantly (P<0.05). Infarction volume in the rats that received the drug at 3 or 6 hours after MCA occlusion was not different from that in the vehicle-treated group. Treatment with SR-49059, when started early after the arterial occlusion, also reduced neurological deficits and ischemic brain edema. Injection of drug at a higher dose (30 mg/kg) also reduced infarction volume and improved functional recovery but was not superior to the lower dose (2 mg/kg) when the drug was administrated at 1 hour after MCA occlusion. Our data show that the selective vasopressin receptor antagonist SR-49059 is a potent neuroprotective agent when used early after onset of arterial occlusion in an embolic focal ischemia model in rats. Further studies are needed in stroke models to better understand its neuroprotective properties when used alone or in combination with thrombolysis.

Delayed multidose treatment with nicotinamide extends the degree and duration of neuroprotection by reducing infarction and improving behavioral scores up to two weeks following transient focal cerebral ischemia in Wistar rats.

A single, delayed dose of nicotinamide (NAm) was shown to be protective against focal cerebral ischemia in rats, but the protection was limited to three to seven days following stroke. The investigation reported here was conducted to examine if the use of multiple doses of NAm, administered after the onset of focal cerebral ischemia, would extend the duration of neuroprotection compared with a single dose treatment regimen. Male Wistar rats were subjected to transient focal cerebral ischemia by occluding the right middle cerebral artery (MCAo) for two hours. Following MCAo, motor and sensory behavioral tests were performed daily and the cerebral infarct volumes were measured at two weeks after sacrifice. Each animal was placed into one of four groups that received either normal saline alone (Group S), one (Group A), two (Group B), or three (Group C) doses of NAm (500 mg/kg). Each animal, therefore, received three treatments over two weeks, with the first dose administered intravenously two hours after the onset of MCAo. Single and multiple doses of NAm reduced the infarction (p < 0.01) and improved (p < 0.05) the neurologic sensory and motor behavior when compared with the saline-treated animals up to two weeks after stroke. Moreover, animals that received multiple doses of NAm recuperated full motor function not different from normal, preoperative motor behavior. Delayed treatment with NAm given as multiple doses, therefore, further enhances the extent and duration of neuroprotection by significantly reducing cerebral infarct volumes, improving neurologic behavioral scores, and confers a complete motor recovery up to two weeks from the onset of focal cerebral ischemia in Wistar rats.

Intravenous brain-derived neurotrophic factor reduces infarct size and counterregulates Bax and Bcl-2 expression after temporary focal cerebral ischemia.

Pretreatment with intraventricular brain-derived neurotrophic factor (BDNF) reduces ischemic damage after focal cerebral ischemia. In this experiment we studied the effect of intravenous BDNF delivered after focal cerebral ischemia on neurological outcome, infarct size, and expression of proapoptotic and antiapoptotic proteins Bax and Bcl-2, respectively. With the use of the suture occlusion technique, the right middle cerebral artery in rats was temporarily occluded for 2 hours. Thirty minutes after vessel occlusion, BDNF (300 microg/kg per hour in vehicle; n=12) or vehicle alone (n=13) was continuously infused intravenously for 3 hours. After 24 hours the animals were weighed and neurologically assessed on a 5-point scale. The animals were then killed, and brains underwent either 2,3,5-triphenyltetrazolium chloride staining for assessment of infarct volume or paraffin embedding for morphology and immunohistochemistry (Bax, Bcl-2). Physiological parameters (mean arterial blood pressure, PO(2), PCO(2), pH, body temperature, glucose) and weight revealed no difference between groups. Neurological deficit was improved in BDNF-treated animals versus controls (P:<0.05, unpaired, 2-tailed t test). Mean+/-SD infarct volume was 229.7+/-97.7 mm(3) in controls and 121.3+/-80.2 mm(3) in BDNF-treated animals (P:<0.05, unpaired, 2-tailed t test). Cortical infarct volume was 155.5+/-78.5 mm(3) in the placebo group and 69.9+/-50.2 mm(3) in the BDNF-treated group (P:<0.05, unpaired, 2-tailed t test). Subcortical infarct volume was 74.1+/-30.6 mm(3) in the placebo group and 51.1+/-26.8 mm(3) in the BDNF-treated group (P:=NS). Bax-positive neurons were significantly reduced in the ischemic penumbra in BDNF-treated animals (P:<0.05, unpaired, 2-tailed t test), whereas Bcl-2-positive neurons were significantly increased in this area (P:<0.001, unpaired, 2-tailed t test). This study demonstrates a neuroprotective effect of BDNF when delivered intravenously after onset of focal cerebral ischemia. As shown here, one possible mechanism of action of neuroprotection of BDNF after focal ischemia appears to be counterregulation of Bax/Bcl-2 proteins within the ischemic penumbra.

Hyperbaric oxygen reduces infarct volume in rats by increasing oxygen supply to the ischemic periphery

Hyperbaric oxygen (HBO) increases oxygen supply to anoxic areas. To examine the therapeutic effect of HBO on ischemic stroke, we measured infarct volume as well as cerebral blood flow (CBF), oxygen supply, and lipid peroxidation in the ischemic periphery. Prospective experimental study in rats. Experimental laboratory in a university teaching hospital. Thirty-eight adult rats. The rats were anesthetized (1% halothane) and intubated. Focal ischemia was induced by ligating the right middle cerebral and right common carotid arteries. Nineteen animals were exposed to 2 hrs of HBO (100% oxygen, 3 atmospheres absolute), initiated 10 mins after the onset of ischemia. The remaining animals were kept at ambient pressure and used as controls. At the initiation of ischemia, CBF measured by a laser-Doppler flow probe placed in the ischemic periphery was reduced to 47%+/-11% and 51%+/-15% of normal levels in animals exposed or not to HBO, respectively. These altered values were not affected further by administration of HBO and remained stable throughout a 2-hr observation period. Arterial oxygen pressure and content were significantly increased to 1571+/-130 torr (209.41+/-17.32 kPa; p < .0001) and 1.03+/-0.04 mmol/dL (p < 0.0001), respectively, in HBO-treated animals compared with nontreated animals (139+/-14 torr [18.53+/-1.87 kPa] and 0.86+/-0.04 mmol/dL, respectively). The calculated increase in the oxygen supply to the ischemic periphery was 20%. The infarct volume of HBO-treated animals measured 24 hrs after the onset of focal cerebral ischemia was significantly reduced by 18% (HBO-treated, 132+/-13 mm3 vs. nontreated, 161+/-29 mm3; p = .02). Lipid peroxidation was unchanged after 120 mins of HBO administration in the cerebral cortex where the laser-Doppler flow probe was placed. HBO at 3 atmospheres absolute reduced infarct volume by increasing oxygen supply to the ischemic periphery without aggravating lipid peroxidation, suggesting that HBO can be useful in treating stroke victims.

Relative neuroprotective effects of dizocilpine and isoflurane during focal cerebral ischemia in the rat.

Both dizocilpine (MK-801) and isoflurane antagonize glutamatergic neurotransmission. In this study, we examined the relative neuroprotective effects of these drugs administered in equianesthetic doses before the onset of focal cerebral ischemia. Rats were anesthetized with 1.0%-1.5% isoflurane and surgically prepared for filament occlusion of the middle cerebral artery (MCAO). After preparation, one group (n = 22) remained anesthetized with 0.7% isoflurane. Another group (n = 18) was given dizocilpine (1 mg/kg intraperitoneally), and isoflurane was discontinued. The third group (n = 18) was allowed to awaken immediately after the onset of ischemia. MCAO persisted for 75 min. Epidural temperature was controlled at 37.5 degrees C during ischemia and the first 22 h of recovery. A 7-day recovery interval was allowed. Total infarction volumes (mean +/- SD) were less for the dizocilpine group (100 +/- 65 mm3) versus the awake group (182 +/- 36 mm3; P = 0.001). Infarction volumes did not differ significantly between the isoflurane group (142 +/- 81 mm3) and either the dizocilpine (P = 0.11) or the awake group (P = 0.15). Isoflurane was examined at doses used clinically but smaller than those found to reduce N-methyl-D-aspartate (NMDA)-mediated injury in vitro. This study supports the hypothesis that NMDA receptor activation is injurious during focal ischemia and that amelioration of focal ischemic brain damage by NMDA receptor antagonists persists under normothermic conditions. Rats underwent focal cerebral ischemia with rigid maintenance of brain normothermia. The glutamate receptor antagonist dizocilpine was effective in reducing cerebral infarction size during persistent conditions of brain normothermia. In contrast, isoflurane administered at equianesthetic doses did not reduce infarction size. This study supports the hypothesis that N-methyl-D-aspartate receptor activation is injurious during focal ischemia and that amelioration of focal ischemic brain damage by N-methyl-D-aspartate receptor antagonists persists under normothermic conditions.

Effect of Tirilazad Mesylate on Middle Cerebral Artery Occlusion/Reperfusion in Nonhuman Primates

Agents with lipid membrane protective properties may theoretically reduce the zone of ischemic damage during cerebral arterial recanalization in the early hours of focal cerebral ischemia. The effect of the putative lipid peroxidation inhibitor tirilazad mesylate (U74006F) on infarction volume and neurological outcome following 3-hour middle cerebral artery occlusion and subsequent reperfusion in an awake baboon model was examined in a blinded, randomized placebo-controlled study. Awake subjects (8 each) were assigned randomly to receive either tirilazad mesylate (3 mg/kg) or matched vehicle given 15 min prior to reperfusion, and again at 2, 4, 12, and 24 h after reperfusion. Neurological status was serially assessed according to a quantitative scale and infarction volumes were computed on perfusion-fixed specimens at 14 days. A 40% reduction in mean total infarction volume index, normalized for basal ganglia volume, was seen in the tirilazad group. Persistent and increased improvement in mean neurological score with tirilazad infusion paralleled that of the placebo. Parallel studies on polymorphonuclear leukocyte responses indicated no significant changes in polymorphonuclear leukocyte reactivity. A reduction in infarction volume, predominantly in the cortex/subcortical white matter, and an improvement in neurological outcome were observed when tirilazad mesylate was given prior to reperfusion, but after the onset of focal cerebral ischemia.

The effect of acute hypocapnia on local cerebral blood flow during middle cerebral artery occlusion in isoflurane anesthetized rats.

Because the effect of hypocapnia on distribution of cerebral blood flow during focal cerebral ischemia is controversial, this investigation was performed in rats to determine whether hypocapnia, instituted immediately after the onset of focal cerebral ischemia, produces a favorable redistribution of blood flow (an "inverse steal") toward the ischemic territory. After surgical preparation during normocapnic isoflurane anesthesia, middle cerebral artery occlusion (MCAO) was performed. Animals were randomized to either immediate institution of hypocapnia (n = 9; PaCO2 23 +/- 2 mmHg) or continued normocapnia (n = 8; PaCO2 40 +/- 2 mmHg). Thirty minutes thereafter, local cerebral blood flow (1-CBF) was determined autoradiographically using 14C-iodoantipyrine. Local cerebral blood flow was determined in four coronal brain sections spanning the distribution of the middle cerebral artery. For the hemisphere ipsilateral to MCAO, the areas of cortex in which CBF fell within three specified CBF ranges (0-6, 6-15, and 15-23 ml/100 g/min) were measured and expressed as a percentage of the total area of cortex in that section. In the hemisphere contralateral to MCAO, to confirm the presence of normal CO2 reactivity in non-ischemic brain in this model, average 1-CBF was determined for the cortex, the subcortex, and the entire hemisphere in each coronal section. Hypocapnia resulted in significantly lower 1-CBF in the cortex, subcortex, and entire hemisphere in all coronal sections of brain contralateral to MCAO. In the hemisphere ipsilateral to MCAO, a favorable redistribution of CBF was not observed. For the three more anterior coronal sections (1-3), a significantly larger percentage of the cortex had 1-CBF in the range of 15-23 ml x 100 g-1 x min-1 in the hypocapnia group animals. In sections 2 and 3, significantly larger areas of cortex had 1-CBF in the range of 6-15 ml x 100 g-1 x min-1 in the hypocapnia group than in the normocapnia group. For all sections, there were no significant differences between hypocapnic and normocapnic groups in the area of cortex with 1-CBF in the range of 0-6 ml x 100 g-1 x min-1. The current study does not provide evidence for the occurrence of a hypocapnia-induced inverse steal phenomenon during acute focal cerebral ischemia of 30 min duration in the rat. The data suggest that, rather than reducing the area of the critically ischemic brain, hypocapnia may increase the size of the region at risk. The data do not support the use of hypocapnia as a therapeutic measure to produce a favorable redistribution of CBF during focal cerebral ischemia of acute onset.

Hemorrhagic transformation following tissue plasminogen activator in experimental cerebral infarction.

The effect of an intravenous infusion of recombinant tissue plasminogen activator on hemorrhagic transformation early after middle cerebral artery territory ischemia was studied in an established awake nonhuman primate (baboon) model. Following 3 hours' occlusion of the middle cerebral artery and 30 minutes' reperfusion in each of 30 baboons, a 60-minute infusion of recombinant tissue plasminogen activator (at three doses: Group A, 0.3 mg/kg, n = 6; Group B, 1.5 mg/kg, n = 6; Group C, 10 mg/kg, n = 6) or normal saline (n = 12) was undertaken. The frequency and volume of intracerebral hemorrhage, the volume of infarction, and clinical alterations were determined by computed tomography at 24 hours and 10 days, neuropathology at 14 days, and serial daily neurologic evaluations, respectively. Peripheral (nonintracranial) hemorrhage (Group A, p = 0.46; Group B, p = 0.015; Group C, p = 0.002) and peak plasma tissue plasminogen activator levels varied directly with the dose of recombinant tissue plasminogen activator. Petechial hemorrhagic infarction was a common finding among the 30 baboons. No significant differences in the incidences or volumes of infarction-related hemorrhage were apparent in any group compared with the respective saline-treated baboons. In pooled data, no significant relation between the volume of hemorrhage and the volume of infarction could be established. We conclude that the incidence and severity of hemorrhagic transformation are not related to infarction size and that recombinant tissue plasminogen activator does not increase the incidence or severity (volume) of hemorrhage when given early (less than or equal to 3.5 hours) after the onset of focal cerebral ischemia in this model.

Alterations in the distribution of water, sodium, potassium, and chloride in brain during the evolution of ischemic cerebral edema.

Abstract Experimental regional cerebral ischemia in the territory of the middle cerebral artery (MCA) in a primate (Macaca mulatta) was produced by selective embolization of the internal carotid artery bifurcation. Determinations of tissue dry weight (percentage) and tissue sodium, potassium, and chloride on samples from the affected and contralateral hemispheres were carried out periodically until 48 hours after the onset of focal cerebral ischemia. Samples from the cortex supplied by the occluded MCA showed excesses in water content, increases in sodium, and decreases in potassium as early as 3 to 4 hours after occlusion. Hemispheric swelling became apparent after 4 to 5 hours, with obvious “gray matter edema.” However, only minimal to moderate increases in the water content of the subcortical white matter (without change in electrolytes) were observed in the same brain sections. Subcortical white matter samples from the affected MCA territory showed gradual increases in water content at 12, 24, and 48 hours, but definite increases in sodium and decreases in potassium were not observed until 24 to 48 hours of ischemia. During this late phase, the “gray matter edema” remained unchanged or underwent partial resolution. Our results agree with data derived from morphological studies suggesting that ischemic cerebral edema develops in a diphasic fashion, with a primary phase of early “gray matter edema” evolving to a secondary phase of late “white matter edema.”

Alterations in the distribution of water, sodium, potassium, and chloride in brain during the evolution of ischemic cerebral edema

Experimental regional cerebral ischemia in the territory of the middle cerebral artery (MCA) in a primate (Macaca mulatta) was produced by selective embolization of the internal carotid artery bifurcation. Determinations of tissue dry weight (percentage) and tissue sodium, potassium, and chloride on samples from the affected and contralateral hemispheres were carried out periodically until 48 hours after the onset of focal cerebral ischemia. Samples from the cortex supplied by the occluded MCA showed excesses in water content, increases in sodium, and decreases in potassium as early as 3 to 4 hours after occlusion. Hemispheric swelling became apparent after 4 to 5 hours, with obvious “gray matter edema.” However, only minimal to moderate increases in the water content of the subcortical white matter (without change in electrolytes) were observed in the same brain sections. Subcortical white matter samples from the affected MCA territory showed gradual increases in water content at 12, 24, and 48 hours, but definite increases in sodium and decreases in potassium were not observed until 24 to 48 hours of ischemia. During this late phase, the “gray matter edema” remained unchanged or underwent partial resolution. Our results agree with data derived from morphological studies suggesting that ischemic cerebral edema develops in a diphasic fashion, with a primary phase of early “gray matter edema” evolving to a secondary phase of late “white matter edema.”