Glutamate antagonist MK-801 attenuates incomplete but not complete infarction in thrombotic distal middle cerebral artery occlusion in Wistar rats

The role of spreading depolarizations and electrographic seizures in early injury progression of the rat photothrombosis stroke model

Spreading depolarization (SD) and seizures are pathophysiological events associated with cerebral ischemia. Here, we investigated their role for injury progression in the cerebral cortex. Cerebral ischemia was induced in anesthetized male Wistar rats using the photothrombosis (PT) stroke model. SD and spontaneous neuronal activity were recorded in the presence of either urethane or ketamine/xylazine anesthesia. Blood-brain barrier (BBB) permeability, cerebral perfusion, and cellular damage were assessed through a cranial window and repeated intravenous injection of fluorescein sodium salt and propidium iodide until 4 h after PT. Neuronal injury and early lesion volume were quantified by stereological cell counting and manual and automated assessment of ex vivo T2-weighted magnetic resonance imaging. Onset SDs originated at the thrombotic core and invaded neighboring cortex, whereas delayed SDs often showed opposite propagation patterns. Seizure induction by 4-aminopyridine caused no increase in lesion volume or neuronal injury in urethane-anesthetized animals. Ketamine/xylazine anesthesia was associated with a lower number of onset SDs, reduced lesion volume, and neuronal injury despite a longer duration of seizures. BBB permeability increase inversely correlated with the number of SDs at 3 and 4 h after PT. Our results provide further evidence that ketamine may counteract the early progression of ischemic injury.

Direct electrophysiological evidence that spreading depolarization-induced spreading depression is the pathophysiological correlate of the migraine aura and a review of the spreading depolarization continuum of acute neuronal mass injury

Spreading depolarization is observed as a large negative shift of the direct current potential, swelling of neuronal somas, and dendritic beading in the brain's gray matter and represents a state of a potentially reversible mass injury. Its hallmark is the abrupt, massive ion translocation between intraneuronal and extracellular compartment that causes water uptake (= cytotoxic edema) and massive glutamate release. Dependent on the tissue's energy status, spreading depolarization can co-occur with different depression or silencing patterns of spontaneous activity. In adequately supplied tissue, spreading depolarization induces spreading depression of activity. In severely ischemic tissue, nonspreading depression of activity precedes spreading depolarization. The depression pattern determines the neurological deficit which is either spreading such as in migraine aura or migraine stroke or nonspreading such as in transient ischemic attack or typical stroke. Although a clinical distinction between spreading and nonspreading focal neurological deficits is useful because they are associated with different probabilities of permanent damage, it is important to note that spreading depolarization, the neuronal injury potential, occurs in all of these conditions. Here, we first review the scientific basis of the continuum of spreading depolarizations. Second, we highlight the transition zone of the continuum from reversibility to irreversibility using clinical cases of aneurysmal subarachnoid hemorrhage and cerebral amyloid angiopathy. These illustrate how modern neuroimaging and neuromonitoring technologies increasingly bridge the gap between basic sciences and clinic. For example, we provide direct electrophysiological evidence for the first time that spreading depolarization-induced spreading depression is the pathophysiological correlate of the migraine aura.

REVIEW ■ : Neuroprotection in Brain Ischemia: An Update (Part I

Ischemic brain injury produced by stroke or cardiac arrest is a major cause of human neurological disability. Steady advances in the neurosciences have elucidated pathophysiological mechanisms of brain ischemia and have suggested many therapeutic approaches directed at specific injury mechanisms to achieve neuroprotection of the acutely ischemic brain. The first portion of this two-part review highlights the differentiating features and pathological mechanisms of focal and global cerebral ischemic injury and summarizes a wealth of recent evidence as to how antagonism of excitatory amino acid neurotoxicity, mediated via NMDA as well as non-NMDA receptors, may offer a means of diminishing the extent of ischemic injury. The Neuroscientist 1:95-103, 1995

Cerebral blood flow restoration and reperfusion injury after ultraviolet laser-facilitated middle cerebral artery recanalization in rat thrombotic stroke

BACKGROUND AND PURPOSE

A reversible model of focal thrombotic stroke was developed in the rat and examined for histological evidence of reperfusion injury after clinically relevant times of recanalization.

METHODS

The distal middle cerebral artery of 28 male Sprague-Dawley rats was occluded by 562-nm laser-driven photothrombosis for 0.5, 2, and 3 hours or permanently (each n=7) and was recanalized by 355-nm UV laser irradiation. Occlusive material was examined by transmission electron microscopy. Cortical cerebral blood flow was monitored by laser-Doppler flowmetry. Brain infarcts were examined histologically at 3 days.

RESULTS

After occlusion, cortical cerebral blood flow was reduced to 33+/-4% of baseline for all groups and was restored to 82+/-9%, 75+/-3%, and 93+/-7% of baseline for the 0.5-, 2-, and 3-hour groups, respectively, following recanalization after 29+/-8, 38+/-20, and 70+/-33 minutes of UV laser irradiation. The thrombotic occlusion contained compactly aggregated platelets but no fibrin, with length (1.2 to 1.8 mm) proportional to the ischemic period. During recanalization, microchannels containing erythrocytes and scattered leukocytes and bordered by intact disaggregated platelets infiltrated the thrombus. Infarct volumes (mm3) at 3 days were 12+/-3 for the permanent case and 8+/-4, 24+/-3, and 30+/-9 for the 0.5-, 2-, and 3-hour cases, respectively, thus demonstrating reperfusion injury histologically in the latter 2 groups. No hemorrhage was seen.

CONCLUSIONS

UV laser-facilitated dissolution of a conventionally refractory platelet thrombus provides a novel and effective method for restoring blood flow without hemorrhagic complications during thrombotic stroke. This was the first observation of histologically confirmed reperfusion injury in such a model.

Effect of magnesium on nitric oxide synthase of neurons in cortex during early period of cerebral ischemia

To investigate the effect of magnesium on nitric oxide synthase (NOS) of neurons in cortex during early cerebral ischemic period, a rat model of middle cerebral artery occlusion (MCAO) was established. The results showed that the NOS activity of neurons in cortex was increased significantly at 15 min after MCAO, reached its peak at 30 min after MCAO and returned to normal levels at 60 min after MCAO. The NOS activity of neurons in the magnesium-treated group was decreased significantly as compared with that in the ischemic group at 15 min and 30 min after MCAO respectively. The results suggested that magnesium could inhibit the elevated NOS activity of neurons in cortex induced by cerebral ischemia.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.

Pathophysiology of the ischemic penumbra--revision of a concept

1. The original concept of the ischemic penumbra surrounding a focus of dense cerebral ischemia is based on electrophysiological observations. In the cortex of baboons following middle cerebral artery occlusion, complete failure of the cortical evoked potential was observed at a cerebral blood flow (CBF) threshold level of approx. 0.15 ml/g/min--a level at which extracellular potassium ion activity was only mildly elevated. With a greater CBF decrement to the range of 0.06-0.10 ml/g/min, massive increases in extracellular potassium occurred and were associated with complete tissue infarction. Thus, the ischemic penumbra has been conceptualized as a region in which CBF reduction has exceeded the threshold for failure of electrical function but not that for membrane failure. 2. Recent studies demonstrate that the penumbra as defined classically by the flow thresholds does not survive prolonged periods of ischemia. The correlation of CBF autoradiograms with diffusion-weighted MR images and the regional distribution of cerebral metabolites reveals that the ischemic core region enlarges when adjacent, formerly penumbral, areas undergo irreversible deterioration during the initial hours of vascular occlusion. At the same time, the residual penumbra becomes restricted to the periphery of the ischemic territory, and its fate may depend critically upon early therapeutic intervention. 3. In the border zone of brain infarcts, marked uncoupling of local CBF and glucose utilization is consistently observed. The correlation with electrophysiological measurements shows that metabolism-flow uncoupling is associated with sustained deflections of the direct current (DC) potential resembling transient depolarizations. Such penumbral cell depolarizations, which are associated with an increased metabolic workload, induce episodes of tissue hypoxia due to the constrained collateral flow, stimulate anaerobic glycolysis leading to lactacidosis, suppress protein synthesis, and, finally, compromise energy metabolism. The frequency of their occurrence correlates with the final volume of ischemic injury. Therefore, penumbral depolarizations are regarded as a key event in the pathogenesis of ischemic brain injury. Periinfarct DC deflections can be suppressed by NMDA and non-NMDA antagonists, resulting in a significant reduction of infarct size. 4. The histopathological sequelae within the penumbra consist of various degrees of scattered neuronal injury, also termed "incomplete infarction." The reduction of neuronal density at the infarct border is a flow- and time-dependent event which is accompanied by an early response of glial cells. As early as 3 hr after vascular occlusion a generalized microglial activation can be detected throughout the ipsilateral cortex. Astrocytic activation is observed in the intact parts of the ischemic hemisphere from 6 hr postocclusion onward. Thus, the penumbra is a spatially dynamic brain region of limited viability which is characterized by complex pathophysiological changes involving neuronal function as well as well as glial activation in response to local ischemic injury.

Effects of etomidate administration on cerebral collateral flow

OBJECTIVE

Augmentation of blood flow to collateral-dependent tissue (CDT) as a result of selective vasodilation of collateral vessels has been shown to occur with various stimuli after middle cerebral artery occlusion. Etomidate, a carboxylated imidazole derivative, is a nonbarbiturate anesthetic that is used clinically both as an anesthetic and as a neuroprotective agent. The effect etomidate has on collateral cerebral vessels is unknown. The purpose of our studies was to test whether etomidate selectively augmented cerebral blood flow (CBF) to CDT during ischemia as an additional mechanism of neuroprotection.

METHODS

A left craniotomy was performed in each of 14 dogs, with the animals under halothane anesthesia. A branch of the middle cerebral artery was occluded and cannulated distally for determination of CDT using a "shadow flow" technique. CBF and vascular pressures were measured and used to calculate vascular resistance. An etomidate infusion (0.1 mg/kg of body weight/min administered intravenously) was started, and CBF and vascular pressures were measured at 10 and 40 minutes. Hypotension was then induced, and CBF and pressures were again measured.

RESULTS

CBF was significantly reduced in all regions of the brain, including CDT, when etomidate was infused. CDT showed a 53.7% reduction in flow, whereas normal CBF was reduced by at least 63.4%. During hypotension, blood flow to CDT was reduced by an additional 42.7%, whereas normal cerebrum was reduced by at least 22.7%. Vascular resistance was increased in all vessels during etomidate infusion.

CONCLUSION

The neuroprotective effects of etomidate do not seem to be through the augmentation of collateral or global CBF.

The effect of the adrenocorticotropin-(4-9) analogue, ORG 2766, and of dizolcipine (MK-801) on infarct volume in rat brain

The purpose of this study was to evaluate whether the synthetic adrenocorticotropin-(4-9) (ACTH-(4-9)) analogue ORG 2766, HMet(O2)-Glu-His-Phe-D-Lys-Phe-OH, which has been shown to have beneficial effects on both the recovery from experimentally induced lesions of the central nervous system and peripheral nerve degeneration, has a protective effect on focal ischemic neuronal damage. The NMDA receptor antagonist dizolcipine (MK-801), a very potent neuroprotective drug, was used as positive reference compound. Isoflurane-anesthetized rats had the middle cerebral artery occluded using either an intravasal or an extravasal technique, because pilot experiments had shown differences in the severity of ischemia for the two middle cerebral artery occlusion techniques. MK-801, 500 microg kg(-1) min(-1), or saline was administered i.v. 30 min after occlusion of the middle cerebral artery. In the ACTH-(4-9) analogue/saline group, 10 and 150 microg/kg of the analogue, or saline was injected s.c. both directly after and 24 h after occlusion. The ACTH-(4-9) analogue treatment had no effect on the infarction volume in either model of middle cerebral artery occlusion, whereas MK-801 caused a significant reduction in the volume of cortical infarction in both models. We conclude that, although ORG 2766 is known to enhance the recovery from experimentally induced lesions of the central nervous system through a neurotrophic action and has proven to have significant beneficial effects on peripheral nerve regeneration, it did not prevent ischemic neuronal damage after intravasal or extravasal middle cerebral artery occlusion in rats. The results with MK-801, which caused significant reductions in the volume of cortical infarction in both models of middle cerebral artery occlusion, with clearly the largest reduction in the intravasal middle cerebral artery occlusion model, again indicate that there are differences in the severity of the cerebral ischemia which the two models produce in the rat brain.

Pre- and postischemic effects of the NMDA receptor antagonist dizocilpine maleate (MK-801) on collateral cerebral blood flow

The authors studied the effects of pre- and postischemic administration of dizocilpine maleate (MK-801) on collateral and regional cerebral blood flow (CBF). The ischemic penumbra appears to benefit most from the neuroprotective effects of MK-801. The precise mechanism by which MK-801 provides this neuroprotection remains controversial. Alterations in CBF have been demonstrated with MK-801 administration, but whether the response is an increase or decrease in flow has remained unclear. A left-sided craniectomy was performed in 20 dogs. A branch of the middle cerebral artery (MCA) was cannulated and collateral blood supply-dependent tissue (CDT) was identified using the "shadow flow" technique. Regional CBF was measured using radiolabeled microspheres. Six dogs received MK-801 (1 mg/kg administered intravenously) before they underwent MCA branch occlusion; the remaining 14 dogs received MK-801 after they underwent MCA occlusion. Cerebral blood flow and vascular pressures were measured 30 and 60 minutes after MK-801 administration. In animals that received MK-801 before MCA occlusion, CBF did not change significantly from baseline values before or after occlusion. In contrast, in animals that received MK-801 after MCA occlusion, CBF was significantly reduced in all regions of the brain, including the CDT. Collateral blood supply-dependent tissue showed a 51.7% reduction in flow, whereas normal CBF was reduced by 29.7%. The MK-801 induced cerebral vasoconstriction in both groups. The neuroprotective effects of MK-801 do not appear to be caused by the augmentation of collateral or global cerebral circulation and, in fact, may block the glutamate-mediated vasodilation that occurs during ischemia.

AMPA receptor antagonist, YM90K, reduces infarct volume in thrombotic distal middle cerebral artery occlusion in spontaneously hypertensive rats

We examined the effects of a potent and selective antagonist of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) subtype of glutamate receptor, YM90K, on brain infarction using a newly developed stroke model of thrombotic distal middle cerebral artery occlusion. Male spontaneously hypertensive rats (5-7 months old) were subjected to photochemically-induced distal middle cerebral artery occlusion as previously described [Stroke 26 (1996) 333-336]. Intravenous infusion of YM90K (n = 8) (5 mg/kg per h for 1 h) or the same amount of vehicle (n = 8) (alkaline saline) was started 5 min after distal middle cerebral artery occlusion. Penumbral cerebral blood flow was determined with laser-Doppler flowmetry. Three days after the ischemic insult, brains were stained with 2,3,5-triphenyltetrazolium chloride and infarct volumes were determined. One hour infusion of YM90K significantly reduced infarct volume by 34% (93 +/- 23 mm3 in control group vs. 61 +/- 25 mm3 in YM90K-treated group, P = 0.017). There were no significant differences in the degrees of cerebral blood flow reduction after distal middle cerebral artery occlusion between the YM90K treated and control groups. YM90K reduces infarct volume in experimental ischemia produced by photothrombotic distal middle cerebral artery occlusion in rats. The present results demonstrated beneficial effects of AMPA receptor blockade on acute ischemic stroke.

L-arginine does not improve cortical perfusion or histopathological outcome in spontaneously hypertensive rats subjected to distal middle cerebral artery photothrombotic occlusion

The potential of nitric oxide (NO) to influence positively or negatively the outcome of mechanically induced focal cerebral ischemia is still controversial. Recent evidence suggests that NO of vascular origin, whether synthesized from exogenously administered L-arginine (L-Arg) or from NO donor compounds, is beneficial but that of neuronal origin is not. However, the therapeutic potential of NO to ameliorate stroke induced by arterial thrombosis has not been reported. We assessed the therapeutic effect of L-Arg administration in spontaneously hypertensive rats (SHR) subjected to permanent photothrombotic occlusion of the distal middle cerebral artery (dMCA). The ipsilateral carotid artery was left unligated to enhance L-Arg delivery into the putative penumbral region. Local CBF (LCBF) was assessed at 30 min by the [14C]iodoantipyrine technique (n = 9), while histological infarct volumes and index of peripheral ischemic cell change were determined at 3 days (n = 7). Rats (n = 9) given 300 mg/kg L-Arg at 18 and 3 h before photothrombotic dMCA occlusion and at 5 min afterward displayed no significant differences in LCBF compared with animals (n = 8) injected with water (the carrier vehicle) and similarly irradiated. Infarct volumes were also similar, being 37.0 +/- 9.7 mm3 (SD) in the vehicle-treated and 49.1 +/- 17.2 mm3 (SD) in the L-Arg-treated groups (both n = 7), as were assessments of ischemic neuronal density in the penumbra. In contrast, L-Arg administered intravenously in a dose of 300 mg/kg to nonischemic SHR (n = 5) increased cortical CBF by approximately 75% during a 70-min observation period. We conclude that thrombotic processes superimposed upon cerebral ischemia may facilitate tissue reactions that offset the potentially beneficial effect of L-Arg, and this caveat must be considered when proposing L-Arg for clinical treatment of focal thrombotic stroke.

Ischemic stroke and incomplete infarction

BACKGROUND

The concept of selective vulnerability or selective loss o f individual neurons, with survival of glial and vascular elements as one of the consequences of a systemic ischemic-hypoxic insult (eg, transient cardiac arrest or severe hypotension), has been recognized for decades. In contrast, selective neuronal death as one of the lesions that may develop in the brain after occluding an intracranial artery is an idea not readily acknowledged in the current medical literature dealing with human stroke.

SUMMARY OF REVIEW

A review of pertinent publications reveals that selective neuronal injury after middle cerebral artery occlusion was observed in autopsy specimens over 40 years ago, although its pathogenesis remains unclear. Recent observations in both humans and animals suggest that selective neuronal necrosis (rather than infarct) is the consequence of either a short-term arterial occlusion or permanent occlusion accompanied by ischemia of moderate severity. During the acute and subacute states of an ischemic stroke, the loss of a limited number of neurons (ie, incomplete infarction) does not result in structural changes discernible by either CT or conventional MRI. However, the loss of a selected number of neurons may be demonstrable in vivo by calculating the corresponding loss of benzodiazepine receptors. The use of specific radiotracers in combination with single-photon emission CT or positron emission tomography allows demonstration of a decrease in gamma-aminobutyric acid-ergic receptor sites at places where many neurons have been lethally injured.

CONCLUSIONS

We aim to alert physicians to the potential development of incomplete brain infarctions in patients with intracranial arterial occlusions. Recognizing incomplete infarcts is particularly important in the context of stroke therapy with thrombolytic and neuroprotective agents. This brain lesion is likely to be the consequence of an arterial occlusion with a resultant ischemia of moderate severity (eg, regional blood flows in the range of 15 to 20 mL x 100 g-1 x min-1).

Induction of spreading depression in the ischemic hemisphere following experimental middle cerebral artery occlusion: effect on infarct morphology

This study was undertaken to test whether transient depolarizations occurring in periinfarct regions are important in contributing to infarct spread and maturation. Following middle cerebral artery (MCA) occlusion we stimulated the ischemic penumbra with recurrent waves of spreading depression (SD) and correlated the histopathological changes with the electrophysiological recordings. Halothane-anesthetized, artificially ventilated Sprague-Dawley rats underwent repetitive stimulation of SD in intact brain (Group 1; n = 8) or photothrombotic MCA occlusion coupled with ipsilateral common carotid artery occlusion (Groups 2 and 3, n = 9 each). The electroencephalogram and direct current (DC) potential were recorded for 3 h in the parietal cortex, which represented the periinffarct border zone in ischemic rats. In Group 2, only spontaneously occurring negative DC shifts occurred; in Group 3, the (nonischemic) frontal pole of the ischemic hemisphere was electrically stimulated to increase the frequency of periinfarct DC shifts. Animals underwent perfusion-fixation 24 h later, and volumes of complete infarction and scattered neuronal injury ("incomplete infarction") were assessed on stained coronal sections by quantitative planimetry. Electrical induction of SD in Group 1 did not cause morphological injury. During the initial 3 h following MCA occlusion, the number of spontaneous periinfarct depolarization in Group 2 (7.0 +/- 1.5 DC shifts) was doubled in Group 3 by frontal current application (13.4 +/- 2.7 DC shifts; p < 0.001). The duration as well as the integrated negative amplitude of DC shifts over time were significantly greater in Group 3 than in Group 2 rats (duration, 5.7 +/- 3.8 vs. 4.1 +/- 2.5 min; p < 0.05). Histopathological examination disclosed well-defined areas of pannecrosis surrounded by a cortical rim exhibiting selectively damaged acidophilic neurons and astrocytic swelling in otherwise normal-appearing brain. Induction of SD in the ischemic hemisphere led to a significant increase in the volume of incomplete infarction (19.0 +/- 6.1 mm3 in Group 3 vs. 10.3 +/- 5.1 mm3 in Group 2; p < 0.01) and of total ischemic injury (100.7 +/- 41.0 mm3 in Group 3 vs. 66.5 +/- 24.7 mm3 in Group 2; p < 0.05). The integrated magnitude of DC negativity per experiment correlated significantly with the volume of total ischemic injury (r = 0.780, p < 0.0001). Thus, induction of SD in the ischemic hemisphere accentuated the development of scattered neuronal injury and increased the volume of total ischemic injury. This observation may be explained by the fact that with limited perfusion reserve, periinfarct depolarization are associated with episodic energy failure in the acute ischemic penumbra.

Simplified model of krypton laser-induced thrombotic distal middle cerebral artery occlusion in spontaneously hypertensive rats

BACKGROUND AND PURPOSE

The effects of thrombotic occlusion of the middle cerebral artery on compromised ischemic tissue may be different from and more severe than those of cerebral ischemia induced by mechanical occlusion of the artery. Photothrombosis, which is based on photochemical damage to the endothelium and subsequent platelet aggregation, is an efficient method to induce thrombosis in vivo. This study aimed to improve and simplify this unique method for an ischemia model of middle cerebral artery occlusion in rats.

METHODS

Male spontaneously hypertensive rats (5 to 6 months old, 300 to 450 g) were anesthetized with halothane, endotracheally intubated, and mechanically ventilated. A krypton laser operating at 568 nm was used to irradiate the exposed distal middle cerebral artery with an intact dura above the rhinal fissure. The photosensitizing dye rose bengal (20 mg/kg body wt) was administered intravenously over 90 seconds starting simultaneously with 4 minutes of laser irradiation at a power of 20 mW to cause thrombotic occlusion of this artery.

RESULTS

The irradiated middle cerebral artery was completely occluded by intraluminal thrombi within 3 minutes after simultaneous laser irradiation and rose bengal infusion. Thrombosed materials were not stained by phosphotungstic acid-hematoxylin stain (ie, aggregated platelets lacked apparent fibrin). The mean volume of 3-day-old infarction, indicated by the lack of staining with 2,3,5-triphenyltetrazolium chloride, was 84.8 +/- 17.4 mm3 (mean +/- SD, n = 6).

CONCLUSIONS

We demonstrated a reproducible and minimally traumatic model of brain infarction induced by the thrombotic distal middle cerebral artery occlusion in rats.

Local cerebral glucose utilization and cytoskeletal proteolysis as indices of evolving focal ischemic injury in core and penumbra

To ascertain the tempo of progression to irreversible injury in focal ischemia, we subjected halothane-anesthetized Sprague-Dawley rats to photochemically induced distal middle cerebral artery occlusion (dMCAO) combined with permanent ipsilateral and 1 h contralateral common carotid artery occlusions. Head temperature was maintained at 36 degrees C. At times centered at either 1.5 or 3 h post-dMCAO, the rate of local glucose metabolism (lCMRgl) was measured by 2-deoxyglucose autoradiography, and cytoskeletal proteolysis was assessed regionally by an immunoblotting procedure to detect spectrin breakdown products. At 1.5 h (n = 5), the cortical ischemic core was already severely hypometabolic (lCMRgl 15.5 +/- 10.8 mumol 100 g-1 min-1, mean +/- SD), whereas the cortical penumbral zone was hypermetabolic (69.0 +/- 9.7). (The lumped constant was verified to be unchanged by methylglucose studies). Neutral red pH studies at this time point showed that both the core and penumbral zones were equally acidotic. By 3 h post-dMCAO (n = 6), lCMRgl in the penumbral zone had fallen to low levels (15.4 +/- 2.2 mumol 100 g-1 min-1) equal to those of the ischemic core (16.7 +/- 4.5). Correspondingly, spectrin breakdown in the ischemic core was advanced at both 2 and 3.5 h post-dMCAO (36 +/- 18% and 33 +/- 18% of total spectrin, respectively), whereas in the penumbral zone spectrin breakdown was less extensive and more highly variable at both times (22 +/- 23% and 29 +/- 16%). We conclude that irreversible deterioration of the ischemic core, as evidenced by the onset of local cytoskeletal proteolysis, begins within 2 h of middle cerebral artery occlusion. In the ischemic penumbra, the transition from glucose hyper- to hypometabolism occurs by 3.5 h and is associated with a milder and more variable degree of spectrin breakdown.