Hyperthermia complicates middle cerebral artery occlusion induced by an intraluminal filament

EEG burst suppression is not necessary for maximum barbiturate protection in transient focal cerebral ischemia in the rat

Barbiturates have been demonstrated to reduce the cerebral metabolic rate (CMR) in a dose-dependent manner but investigations of a dose-response relationship for their neuroprotective efficacy are scant. It has been suggested that barbiturates possess other mechanism of action that may be critical to their protective effect. If so, it is conceivable that the peak effect of such mechanisms does not parallel the reduction in CMR. Thus, maximal neuroprotection may be achieved with a substantially lower dose of the drug. Thirty Sprague-Dawley rats were subjected to 2 h of middle cerebral artery occlusion while either anesthetized with (1) halothane (control) or (2) intravenous thiopental titrated to cause mild EEG suppression or (3) thiopental titrated to maintain EEG burst suppression. Cortical blood flow was recorded by continuous bilateral laser Doppler flowmetry (LDF). Infarct volume was assessed after 3 h of reperfusion. Low-dose thiopental decreased blood flow to 80% of baseline and high-dose thiopental to 70% of baseline. LDF did not indicate improvement of blood flow by thiopental in the ischemic area. Compared to controls, low-dose thiopental significantly decreased infarct volume by 28% and high-dose thiopental by 29%. The results of this study and a review of literature indicate that barbiturates provide cerebral protection but that the magnitude of this effect has been overestimated. Other mechanisms than CMR reduction seem to contribute to their beneficial effects, and high doses administered to the point of burst suppression may not be required to obtain maximal protection.

Neuroprotective effect of the novel glutamate AMPA receptor antagonist YM872 assessed with in vivo MR imaging of rat MCA occlusion

The neuroprotective effect of post-ischemic treatment with the novel, highly water-soluble, glutamate AMPA receptor antagonist YM872 was evaluated by using MR imaging and histopathology of rats subjected to permanent MCA occlusion. Two treatment groups with continuous i.v. infusion of 20 mg kg-1 h-1 YM872 during either the first 4 h or first 24 h after MCA occlusion, called 4 h YM872 treatment group (n=9) and 24 h YM872 treatment group (n=8) respectively, were compared to a control group (n=8). The main end-point was T2 weighted MR imaging and histopathology 24 h after MCA occlusion. Also the time evolution of the ischemic tissue damage was studied by diffusion weighted MR imaging 412 and 24 h after MCA occlusion. The volume of ischemic tissue damage as assessed by diffusion weighted MR imaging 412 h after MCA occlusion was significantly smaller in both YM872 treatment groups (99+/-52 mm3 and 102+/-44 mm3 compared to 186+/-72 mm3 in the control group, +/-S.D. and p=0.008). The infarct volume as assessed by T2 weighted MR imaging 24 h after MCA occlusion was significantly smaller only in the 24 h YM872 treatment group (262+/-57 mm3 compared to 366+/-49 mm3 in the control group, +/-S.D. and p=0.01) while the infarct volume in the 4 h YM872 treatment group (357+/-88 mm3) was similar to the control group. YM872 treatment significantly reduced the infarct volume 24 h after MCA occlusion when the drug was administered as continuous infusion during the 24-h observation period.

Mild hypothermia--a revived countermeasure against ischemic neuronal damages

Although hypothermia as a means of cerebral protection against and resuscitation from ischemic damage has a history of approximately six decades, extensive studies, both in basic and clinical fields, on the mechanisms, effects and methods of mild hypothermia at temperatures no less than 31 degrees C have started only in the last decade. In experiments on rodents, hypothermia in the postischemic period that is introduced up to several hours after reperfusion and is maintained for one day followed by a slow rewarming, significantly protects hippocampal neurons against damage. The mode of action of hypothermia is apparently non-specific and multi-focal in widely progressing cascade reactions in ischemic cells; namely, suppressing: (1) glutamate surge followed by; (2) intraneuronal calcium mobilization; (3) sustained activation of glutamate receptors; (4) dysfunction of blood brain barrier; (5) proliferation of microglial cells; and (6) production of superoxide anions and nitric oxide. In addition, mild hypothermia modulates processes in ischemic condition at the level of cell nucleus, such as the binding of transcription factor AP-1 to DNA, and ameliorates the depression of protein synthesis. This non-specific and widely affecting manner might explain why hypothermia is superior to any medicine developed. Recent clinical trials of mild hypothermia in various individual institutions have revealed significantly beneficial outcomes in some cases, along with an accumulation of practical knowledge of techniques and treatments. Large scale randomized studies involving multiple institutions as well as exchange of informations and ideas are needed for further development of hypothermia treatment.

A critical reevaluation of the intraluminal thread model of focal cerebral ischemia: evidence of inadvertent premature reperfusion and subarachnoid hemorrhage in rats by laser-Doppler flowmetry

BACKGROUND AND PURPOSE

The intraluminal thread model for middle cerebral artery occlusion (MCAO) has gained increasing acceptance. Numerous modifications have been reported in the literature, indicating that the technique has not been standardized. The present study was performed to evaluate and optimize the reliability of this model.

METHODS

One hundred Sprague-Dawley rats were subjected to MCAO by 2 different intraluminal filaments. Cortical blood flow was continuously monitored over both hemispheres by laser-Doppler flowmetry (LDF). In part I (3-0 filament), we evaluated the incidence of adequate MCAO, subarachnoid hemorrhage (SAH), intraluminal thrombus formation, and the effects of heparinization. In part II (silicone-coated 4-0 filament), we also determined the influence of insufficient MCAO on morphological and functional outcome and the incidence of postischemic hyperthermia.

RESULTS

In part I, SAH occurred in 30% and premature reperfusion in 24%. All animals with a decrease in contralateral flow had suffered SAH. Thrombus formation was not observed in any group. In part II, SAH occurred in 8% and premature reperfusion in 26%. There was no difference in outcome between rats with primary MCAO and rats with filament correction. Animals with uncorrected premature reperfusion had significantly smaller infarct volumes and fewer neurological deficits.

CONCLUSIONS

SAH and insufficient MCAO may be more common in the intraluminal thread model than previously reported. Inadvertent premature reperfusion contributes to the interanimal variability associated with this model. The incidence of valid experiments increases with the use of a silicone-coated 4-0 filament. Continuous bilateral LDF is indispensable to monitor adequate MCAO and is highly sensitive to recognize SAH.

Hyperglycemia-exaggerated ischemic brain damage following 30 min of middle cerebral artery occlusion is not due to capillary obstruction

Transient focal ischemia of brief duration (15-30 min) gives rise to brain damage. In normoglycemic animals this damage usually consists of selective neuronal necrosis (SNN), and is largely confined to the lateral caudoputamen. In hyperglycemic subjects damage occurs more rapidly, involves also neocortical areas, and is often of the pan-necrotic type ('infarction'). Since experiments on forebrain ischemia of 30 min duration suggest that microcirculatory compromise develops during recirculation, we studied whether focal ischemia of the same duration, followed by reperfusion for 1, 2 or 4 h, leads to microcirculatory dysfunction. To test this possibility, we fixed the tissue by perfusion and counted the number of formed elements (leukocytes, macrophages and erythrocytes) in capillaries and postcapillary venules. Furthermore, capillary patency was evaluated following in vivo injection of Evan's blue. Histopathological examination of tissue fixed by perfusion after 1, 2 and 4 h of recirculation showed an increasing density of SNN in the caudoputamen of normoglycemic animals. Hyperglycemic, but not normoglycemic, animals showed pan-necrotic lesions ('infarction') after 4 h of recirculation. As a result, the total volume of tissue damage (SNN plus infarction) was larger in hyper- than in normoglycemic animals at 2 and 4 h of recirculation. In addition, hyperglycemic animals showed involvement of neocortex which increased with the time of reperfusion. In the ischemic hemisphere, between 5 and 10% of counted capillaries contained formed elements. However, since hyperglycemic animals contained an equal (or smaller) amount of cells the results did not suggest that capillary 'plugging' could explain the aggravated damage. Moreover, both normo- and hyperglycemic animals showed close to 100% capillary patency. The results thus fail to support the notion that the aggravation of focal ischemic damage by hyperglycemia is due to obstruction of microvessel by swelling or leukocyte adherence.

MDL 101,002, a free radical spin trap, is efficacious in permanent and transient focal ischemia models

The present work describes the neuroprotective effects of the free radical spin trap, MDL 101,002, in models of permanent and transient focal ischemia. Permanent focal ischemia was carried out by occlusion of the distal segment of the middle cerebral artery (MCA) and CCA's in Spontaneously Hypertensive (SH) and Wistar rats. Transient focal ischemia was undertaken by occluding the origin of the MCA for 180 min by the intraluminar monofilament method in Wistar rats. With permanent distal MCA occlusion in SH rats, 100 mg/kg i.v. at 30 min post-ischemia resulted in a significant 40% reduction in infarct volume. Similarly, a 75 mg/kg bolus + 45 mg/kg-h dose of MDL 101,002 given i.v. at 5 min post-ischemia resulted in a 90% or 60% decrease in infarct volume in the mixed permanent/transient distal MCA model with Wistar rats using 120 or 180 min of CCA occlusion, respectively. When full reperfusion was established, after 180 min of occlusion in the proximal MCA model, a dose of 40 mg/kg + infusion and 75 mg/kg + infusion resulted in a significant 50% and 70% decrease in ischemic damage, respectively. MDL 101,002 is clearly an effective neuroprotective agent in all models examined. This work would suggest that this novel cyclic nitrone spin trap affords effective neuroprotection and is useful for the treatment of ischemic stroke.

Amelioration of ischaemia-induced neuronal death in the rat striatum by NGF-secreting neural stem cells

The objective of the present study was to explore whether grafted immortalized neural stem cells, genetically modified to secrete nerve growth factor (NGF), can ameliorate neuronal death in the adult rat striatum following transient middle cerebral artery occlusion (MCAO). One week after cell implantation in the striatum, animals were subjected to 30 min of MCAO. Striatal damage was evaluated at the cellular level after 48 h of recirculation using immunocytochemical and stereological techniques. The ischaemic insult caused an extensive degeneration of projection neurons, immunoreactive for dopamine- and adenosine 3': 5'-monophosphate-regulated phosphoprotein with a molecular weight of 32 kilodaltons (DARPP-32). 3H-Thymidine autoradiography demonstrated surviving grafted cells in the lesioned striatum in all transplanted rats. The loss of striatal projection neurons was significantly reduced (by an average of 45%) in animals with NGF-secreting grafts, whereas control cells, not producing NGF, had no effect. The neuroprotective action of NGF-secreting grafts was also observed when the total number of striatal neurons immunopositive for the neuronal marker NeuN was quantified, as well as in cresyl violet-stained sections. The present findings indicate that administration of NGF by ex vivo gene transfer and grafting of neural stem cells can ameliorate death of striatal projection neurons caused by transient focal ischaemia.

The calmodulin antagonist trifluoperazine in transient focal brain ischemia in rats. Anti-ischemic effect and therapeutic window

BACKGROUND AND PURPOSE

This study was performed to assess the efficacy and the therapeutic window for the calmodulin antagonist trifluoperazine in experiments involving transient middle cerebral artery (MCA) occlusion.

METHODS

Male Wistar rats were subjected to transient (2 hours) MCA occlusion by an intraluminal filament technique. Trifluoperazine (5.0 mg.kg-1) was injected intraperitoneally 5 minutes, 1 hour, or 2 hours after the induction of ischemia. Drug administration was repeated 24 hours after the first injection. Neurological scores and infarct volumes were evaluated at 48 hours of reperfusion. The effect of trifluoperazine on cortical blood flow was studied with continuous laser-Doppler flowmetry.

RESULTS

The median value of neurological scores in the control rats (n = 7) was 3, while those in the treated groups were 1 (5-minute group; n = 7, P < .05) and 2 (1-hour and 2-hour groups; each n = 7). The percentage of infarct volume in the control rats was 34.8 +/- 4.9% (mean +/- SD), while those in the treated groups were 11.3 +/- 12.3% (5-minute group; P < .01), 24.8 +/- 15.1% (1-hour group), and 28.8 +/- 8.3% (2-hour group). Trifluoperazine, given at 5 minutes after ischemia, had no influence on blood flow in the neocortical penumbra during and after ischemia.

CONCLUSIONS

The results demonstrate that trifluoperazine markedly reduces infarct volume after 2 hours of MCA occlusion when given 5 minutes after the induction of ischemia. However, the therapeutic window for trifluoperazine seems narrow since the drug had no significant effect when given after 1 or 2 hours.

The immunosuppressant drug FK506 ameliorates secondary mitochondrial dysfunction following transient focal cerebral ischemia in the rat

Recirculation following 2 h of focal ischemia due to transient middle cerebral artery (MCA) occlusion has previously been found to be accompanied by an initial, partial recovery of the cellular bioenergetic state and of mitochondrial respiratory functions, with secondary deterioration during the first 2-4 h of reflow. Both the free radical spin trap alpha-phenyl-N-tert-butyl nitrone (PBN) and the immunosuppressant drug FK506 ameliorate the damage incurred by the 2-h period of focal ischemia, even when given 1-3 h after the start of the recirculation. The primary objective of this study was to find out if FK506, like PBN, prevents the secondary deterioration of mitochondrial function, as this can be studied in vitro. Since this proved to be the case, we addressed the question of whether the secondary mitochondrial dysfunction and bioenergetic failure were related to a secondary compromise of microcirculation and cellular oxygen delivery. Six groups of male Wistar rats were studied for measurement of mitochondrial respiratory activity (total, n = 36). One group was used as control (n = 6). In the other groups of animals, MCA occlusion of 2 h duration was induced by an intraluminal filament technique, Neocortical focal and perifocal ("penumbra") tissues were sampled after 2 h of ischemia (n = 6) and after 1 h (n = 6), 2 h (n = 6 with vehicle), and 4 h (n = 6 with vehicle; n = 6 with FK506) of recirculation. The vehicle or 1.0 mg.kg-1 of FK506 was injected intravenously after 1 h of recirculation. Homogenates were prepared, and stimulated (+ADP), nonstimulated (-ADP), and uncoupled respiratory rates were measured polarographically. The uncoupling agent used was carbonyl cyanide m-chlorophenylhydrazone. Local CBF and tissue oxygen tension were evaluated by laser-Doppler flowmetry and PO2 microelectrodes, respectively, throughout the whole periods of 2 h of ischemia and 4 h of recirculation, using a remote MCA occlusion technique. After 2 h of ischemia, the penumbra showed a moderate decrease and the focus a marked decrease in ADP-stimulated and uncoupled respiratory rates, with a marked fall in the respiratory control ratio, defined as ADP-stimulated divided by nonstimulated respiration. Recirculation (1 h) brought about partial recovery, but continued reflow (2 and 4 h) was associated with a secondary deterioration of respiratory functions. The secondary deterioration was prevented by FK506. The results thus confirm previous findings showing that secondary mitochondrial dysfunction occurs following transient focal cerebral ischemia and demonstrate that FK506, like PBN, improves the in vitro performance of mitochondria in focal and penumbral areas. Following MCA occlusion, local CBF in a penumbral area and tissue PO2 in a focal area decreased to about 30 and 5% of control, respectively. However, recirculation brought about rapid recovery of blood flow and oxygen delivery. During the whole 4-h period of recirculation, local CBF and tissue PO2 were maintained close to 100% and at about 160% of the preischemic level, respectively. The results make it highly unlikely that the secondary bioenergetic failure during recirculation is due to a compromised microcirculation. It follows that oxygen delivery is not rate-limiting for recovery events. Very likely, FK506 (and PBN) acts at the cellular level to improve mitochondrial energy functions.

Regional cerebral blood flow during and after 2 hours of middle cerebral artery occlusion in the rat

In this study we explored if the secondary bioenergetic failure, which occurs a few hours after recirculation, following transient middle cerebral artery occlusion (MCAO) in rats, is caused by a compromised reflow. We induced 2 hours of MCAO and measured CBF at the end of the ischemia, as well as 15 minutes, 1, 2, and 4 hours after the start of recirculation, using autoradiographic or tissue sampling 14C-iodoantipyrine techniques. After 2 hours of MCAO, the autoradiographically measured CBF in the ischemic core areas was reduced to 3 to 5% of contralateral values. The reduction in CBF was less in neighboring, penumbral areas. After recirculation, flow already normalized in core tissues after 15 minutes, and remained close to normal for the 4 hours recirculation period studied. However, in penumbral tissues, recovery CBF values were usually below normal. The results show that tissues that are heavily compromised by the 2-hour period of ischemia and are destined to incur infarction, show a "relative hyperemia" during recirculation. In fact, some areas of the previously densely ischemic tissue showed overt hyperperfusion. This finding raises the question whether the relative or absolute hyperemia reflects events that are pathogenetically important. Because drugs that clearly ameliorate the final damage incurred fail to alter the relative hyperperfusion of previously ischemic tissues, it is concluded that vascular events in the reperfusion period do not play a major role in causing the final damage.

Superior neuroprotective efficacy of a novel antioxidant (U-101033E) with improved blood-brain barrier permeability in focal cerebral ischemia

BACKGROUND AND PURPOSE

The vascular endothelium and parenchyma of the brain have the potential to generate free radicals under pathological conditions, but it is unclear which of these two sites prevails in the production of free radicals and should be the primary target of therapeutic intervention. To clarify this issue, we compared the neuroprotective properties of a 21-aminosteroid (U-74389G) that acts on the microvasculature and a pyrrolopyrimidine (U-101033E), a novel antioxidant compound that has significantly improved potential to enter the brain parenchyma.

METHODS

In Sprague-Dawley rats the middle cerebral artery was occluded for 90 minutes by an intraluminal filament. Local cortical blood flow was recorded by bilateral laser Doppler flowmetry throughout ischemia and 1 hour of reperfusion. Three groups of rats were studied: controls that received vehicle only and animals that received either U-74389G or U-101033E. Neurological examinations were performed daily, and infarct size was assessed histologically 7 days after ischemia.

RESULTS

U-101033E reduced infarct volume significantly by 51%, whereas U-74389G led to a nonsignificant decrease in infarct volume. U-101033E improved neurological function immediately after ischemia, whereas U-74389G led to improvement only at the end of the observation period. Laser Doppler measurements showed no significant difference in local cortical blood flow among the treatment groups.

CONCLUSIONS

We conclude that for treatment of transient focal ischemia, an antioxidant that crosses the blood-brain barrier might be superior to agents that predominantly act on the endothelium of the cerebral microvasculature.

Postischemic hypothermia. A critical appraisal with implications for clinical treatment

The use of hypothermia to mitigate cerebral ischemic injury is not new. From early studies, it has been clear that cooling is remarkably neuroprotective when applied during global or focal ischemia. In contrast, the value of postischemic cooling is typically viewed with skepticism because of early clinical difficulties and conflicting animal data. However, more recent rodent experiments have shown that a protracted reduction in temperature of only a few degrees Celsius can provide sustained behavioral and histological neuroprotection. Conversely, brief or very mild hypothermia may only delay neuronal damage. Accordingly, protracted hypothermia of 32-34 degrees C may be beneficial following acute clinical stroke. A thorough mechanistic understanding of postischemic hypothermia would lead to a more selective and effective therapy. Unfortunately, few studies have investigated the mechanisms by which postischemic cooling conveys its beneficial effect. The purpose of this article is to evaluate critically the effects of postischemic temperature changes with a comparison to some current drug therapies. This article will stimulate new research into the mechanisms of lengthy postischemic hypothermia and its potential as a therapy for stroke patients.

Cortical infarct volume is dependent on the ischemic reduction of perifocal cerebral blood flow in a three-vessel intraluminal MCA occlusion/reperfusion model in the rat

Occlusion of the middle cerebral artery (MCA) causes a reduction of cerebral blood flow (CBF), which shows a progressive decrease from the periphery to the core of the MCA territory. The severity of ischemia is dependent on the duration of the ischemic episode and degree of CBF reduction. Fixing the ischemic episode to 1 h, we have examined whether or not cortical infarct size was related to the degree of CBF reduction in a perifocal cortical area in rats. One-hour intraluminal MCA occlusion accompanied with bilateral common carotid artery (CCA) occlusion (three-vessel occlusion/reperfusion model) was carried out in Sprague-Dawley rats and CBF was monitored with laser-Doppler flowmetry in the fronto-parietal cortex, an area which is perifocal to the core of the MCA territory. Finally, infarct size was measured 7 days later and was related to the corresponding CBF decrease. Sequential ipsilateral CCA, MCA and contralateral CCA occlusions produced reductions of CBF to 96%, 52% and 33% of baseline, respectively. Cortical infarct volume was found to be dependent on the corresponding reduction of perifocal cortical CBF during the ischemic episode. These results show that the reduction of CBF in the periphery of the MCA territory during 1-h focal ischemia determines infarct size in a three-vessel occlusion/reperfusion model.

Neuroprotective effect of NMDA receptor glycine recognition site antagonism persists when brain temperature is controlled

Several lines of inquiry have indicated that glycine plays an important role in both glutamatergic neurotransmission and pathophysiology of cerebral ischemia. However, subacute outcome trials demonstrating the efficacy of glycine antagonists as neuroprotectants have not been performed with rigorous control of brain temperature. In this study, we investigated the effect of N-methyl-D-aspartate (NMDA) receptor glycine recognition site antagonism in a temperature-controlled rodent model of transient focal ischemia. Male Wistar rats underwent 75 min of intraluminal middle cerebral artery occlusion (MCAO). During MCAO and the first 24 h of reperfusion, rats (n = 10) were administered e55-nitro-6,7-dichloro-2,3-quinoxalinedione (ACEA 1021) i.v. as a bolus infusion of 5 mg/kg followed by 3.5 mg/kg/h (Low-Dose) or 10 mg/kg followed by 7 mg/kg/ h (High-Dose) for 24 h. Cortical temperature was controlled at 38.0 +/- 0.1 degrees C during MCAO and the first 6 h of reperfusion. A 7-day recovery interval was allowed. Mean total infarct volume was reduced by approximately 40% in both high- and low-dose groups (p < 0.01). The preponderance of infarct reduction occurred in the cortex (p < 0.01). Neurologic function correlated with the size of cerebral infarct (p = 0.001). Neurologic grade was similarly improved by treatment with either dose (p = 0.01). These results demonstrate that neuroprotection achieved by antagonism of the glycine recognition site persists when brain temperature is controlled, indicating a potent mechanism of action other than attenuating a hyperthermic response to ischemia.

Dextromethorphan protects against cerebral injury following transient, but not permanent, focal ischemia in rats

Dextromethorphan (DM) has been observed to afford neuroprotection in a variety of in vitro and in vivo experimental models of CNS injury. We have evaluated the neuroprotective activity of DM following both transient (2 h) and permanent focal cerebral ischemia in the rat. Middle cerebral artery occlusion (MCAO) was produced in male Sprague-Dawley rats using the intraluminal filament technique. Animals were dosed s.c with 20 mg/kg DM at 0.5, 1, 2, 4, and 6 hours post occlusion. Analysis of brain injury was performed 24 hours after permanent occlusion or reperfusion. Following transient MCAO, vehicle treated rats exhibited a total infarct volume of 203 +/- 33 mm3. DM produced a 61% reduction in infarct volume to 79 +/- 13 mm3. Permanent MCAO produced a larger infarct volume (406 +/- 44 mm3) which was not significantly reduced in size by treatment with DM (313 +/- 58 mm3). Infarcted hemispheric oedema was not different in vehicle treated rats following transient or permanent MCAO and was not reduced by DM in either group. Following transient MCAO, rectal temperature was elevated 1,2 and 5 hours post occlusion. While not inducing hypothermia or altering physiological parameters such as blood pressure and blood gases, DM attenuated this injury-related increase in temperature, an effect which appeared to correlate with its ability to protect neurons in temperature regulating hypothalamic centres. The DM-induced reduction in infarction demonstrated in our model of transient focal cerebral ischemia provides further support for the in vivo neuroprotective activity of this compound. Importantly, these data demonstrate the limited neuroprotective efficacy of DM when attempting to combat more severe focal ischemic injuries and imply that drug-induced hypothermia is not ultimately responsible for its protective action.

Extracellular potassium in a neocortical core area after transient focal ischemia

BACKGROUND AND PURPOSE

Occlusion of the middle cerebral artery (MCAO) results in bioenergetic failure in the densely ischemic core areas. During reperfusion, transient recovery of the bioenergetic state is followed by secondary deterioration. In this study, we recorded the extracellular potassium concentrations in the cortical core during 2 hours of MCAO, as well as during recovery. One group of animals with recirculation periods of 6 to 8 hours was given the free radical spin trap alpha-phenyl-N-tert-butyl nitrone (PBN).

METHODS

The experiments were performed on adult male Wistar rats (305 to 335 g). The right MCA was occluded by an intraluminal filament technique. For [K+]e measurements a craniotomy was made over the right cortex, and an ion-sensitive microelectrode was lowered into the ischemic focus. Recording of [K+]e was continued for 2 hours. After 48 hours of reperfusion, infarction size was estimated with 2,3,5-triphenyltetrazolium chloride.

RESULTS

During MCA occlusion, [K+]e rose to approximately 60 mmol/L. However, several animals showed transient (and partial) periods of repolarization accompanied by a decrease in [K+]e. Immediately on reperfusion, the [K+]e started to recover and reached baseline levels (2.5 mmol/L) within 3 to 5 minutes. During the first 6 hours of recovery, [K+]e was stable at about 2.5 mmol/L, but after this period a moderate increase in the [K+]e was observed. This was not observed in animals injected with PBN 1 hour after reperfusion.

CONCLUSIONS

The data suggest that delayed cell membrane dysfunction, as reflected in a rise in [K+]e, occurs after about 6 hours of reperfusion and that treatment with PBN in a single dose ameliorates or delays such deterioration of plasma membrane function.

DNA fragmentation and HSP70 protein induction in hippocampus and cortex occurs in separate neurons following permanent middle cerebral artery occlusions

DNA nick end-labeling (TUNEL) and heat shock protein (HSP)70 immunocytochemistry were performed on the same brain sections 1 (n = 6), 3 (n = 12), and 7 (n = 7) days following permanent middle cerebral artery (MCA) occlusions produced in adult rats using the endovascular carotid suture method. In the cortex at 1 and 3 days following MCA occlusions, HSP70 immunoreactive neurons were located outside areas of infarction and showed little evidence of DNA fragmentation. HSP70-stained cortical neurons were intermingled with TUNEL cells near the infarct, but extended for greater distances away from the infarct. DNA fragmentation occurred in CA1 hippocampal neurons in 39% of the animals at 1 and 3 days following ipsilateral MCA occlusion. Bilateral DNA fragmentation occurred in CA1 neurons in one subject. HSP70 protein was expressed in CA1 hippocampal neurons in nine of 18 (50%) animals at 1 and 3 days following MCA occlusions, including all animals that exhibited hippocampal DNA fragmentation. Three animals had bilateral expression of HSP70 in CA1 neurons. Cells that stained for either HSP70 protein or DNA fragmentation existed in close proximity to one another. Approximately 5-7% of HSP70-stained cells were TUNEL stained and 3% of TUNEL-positive cells also stained for HSP70. There was no HSP70 staining or DNA fragmentation in the brains of sham-operated controls (n = 4) or in the brains of animals 7 days following MCA occlusions. These data suggest that ischemic cells capable of translating HSP70 protein generally do not undergo DNA fragmentation. These data support the concept that most HSP70 protein-containing neurons in the cortical "penumbra" and hippocampus survive ischemic injury and are "reversibly injured." It is shown that CA1 hippocampal pyramidal neurons die or are reversibly injured in approximately 50% of animals following permanent MCA occlusions. Although the mechanism of this hippocampal injury is unknown, it could relate to transynaptic activation of N-methyl-D-aspartate (NMDA) receptors that mediate induction of early genes in hippocampus.

Middle cerebral artery occlusion in the rat by intraluminal suture. Neurological and pathological evaluation of an improved model

BACKGROUND AND PURPOSE

The purpose of the present study was to evaluate a modified method of intraluminal suture occlusion of the middle cerebral artery (MCA) on the volume of brain infarction and on neurobehavioral function in rats subjected to a temporary focal ischemic insult.

METHODS

Male Sprague-Dawley rats were anesthetized with halothane and subjected to 60 minutes or 2 hours of temporary MCA occlusion (MCAo) by an intraluminal thread. In one group of rats, the suture was coated with poly-L-lysine, while in a second group, a conventional uncoated suture was used. Behavioral function was evaluated at 50 to 60 minutes after occlusion and during a 3-day period after MCAo. Three days after MCAo brains were perfusion-fixed and infarct volumes were measured.

RESULTS

In rats with 60-minute MCAo, only 3 of 7 animals with uncoated sutures had infarcts, whereas in the group with poly-L-lysine-coated sutures, all rats (n = 7) exhibited infarction (P = .009, Fisher's exact test). With 2 hours of MCAo, total infarct volume (corrected for brain edema) was significantly larger in rats with poly-L-lysine-coated sutures than in the group with uncoated sutures (mean +/- SEM, 122.1 +/- 4.8 versus 67.0 +/- 18.2 mm3, respectively; P = .03; n = 4 in each group). In the 2-hour MCAo study, infarct volumes in the uncoated-suture group tended to be variable and inconsistent (coefficient of variation, 54%) compared with the group in which sutures were coated with poly-L-lysine, in which a highly consistent infarct was produced (coefficient of variation of infarct volume, 8%).

CONCLUSIONS

Reversible MCAo in which a poly-L-lysine-coated intraluminal suture was used proved to be a reliable and effective modification of this technique, yielding consistently larger infarcts and greatly reduced interanimal variability.

Inducible nitric oxide synthase gene expression in vascular cells after transient focal cerebral ischemia

BACKGROUND AND PURPOSE

We investigated whether inducible nitric oxide synthase (iNOS) is expressed after transient cerebral ischemia and, if so, we sought to define the temporal profile and cellular localization of the expression and the role of iNOS in the mechanism of ischemic brain injury.

METHODS

The middle cerebral artery in rats was occluded for 2 hours by an intraluminal filament. The occurrence of transient ischemia and reperfusion was confirmed by laser-Doppler flowmetry (n = 5). iNOS message in the ischemic neocortex was determined by reverse-transcription polymerase chain reaction. iNOS enzymatic activity was assessed by citrulline assay. The cellular localization of iNOS expression was determined by immunohistochemistry.

RESULTS

iNOS mRNA was maximally expressed in postischemic brain at 12 hours and was not present at 4 days (n = 3 per time point). iNOS mRNA was not observed in the contralateral cerebral cortex. iNOS enzymatic activity developed in the postischemic brain between 12 and 24 hours (P < .05) and subsided at 4 days (n = 4 to 8 per time point). iNOS immunoreactivity in the ischemic region was restricted to the wall of capillaries and of larger blood vessels at 12 to 24 hours. In regions of early necrosis, inflammatory cells were iNOS positive. Treatment with the iNOS inhibitor aminoguanidine (n = 5; 100 mg/kg IP, BID for 4 days), starting 6 hours after ischemia, reduced infarct size in neocortex by 36 +/- 7% in comparison with vehicle-treated controls (n = 5) (P < .05).

CONCLUSIONS

Transient focal ischemia leads to iNOS expression in postischemic brain. However, the spatial and temporal patterns of expression differ from those occurring in permanent ischemia: iNOS is induced earlier and predominantly in vascular cells rather than in neutrophils. Thus, the temporal profile and localization of postischemic iNOS expression depend on the nature of the ischemic insult. The finding that aminoguanidine reduces infarct size adds further support to the hypothesis that postischemic iNOS expression contributes to ischemic brain damage.

The effects of gamma 2-melanocyte-stimulating hormone and nimodipine on cortical blood flow and infarction volume in two rat models of middle cerebral artery occlusion

We observed that the pro-opiomelanocortin-derived neuropeptide, gamma 2-melanocyte-stimulating hormone (gamma 2-MSH), has various peripheral and central hemodynamic effects in the rat, including a marked enhancing effect on cerebral blood flow. This hemodynamic profile might be of interest in the pharmacotherapeutic approach to acute cerebral ischemia. Being an adrenocorticotropin (ACTH) analogue, gamma 2-MSH might also possess direct neuronal protective properties. Therefore, in two rat models of focal cerebral ischemia we studied the effects of gamma 2-MSH, with nimodipine, a Ca2+ channel antagonist, as a reference compound, on parasagittal laser-Doppler-assessed cortical blood flow and infarction volume. In isoflurane-anesthetized Wistar and F344 rats i.v. bolus infusions (four in total) of gamma 2-MSH or nimodipine or their vehicle controls were given 1 h before, 1 min after, and 1 h and 2 h after occlusion of the middle cerebral artery. We used both an intravasal and an extravasal middle cerebral artery occlusion technique because pilot experiments had shown differences in the severity of ischemia with the two techniques. gamma 2-MSH (100 nmol/kg in 1 min) increased cortical blood flow significantly but transiently, both pre- and post-ischemically, whereas nimodipine (20 micrograms/kg in 1 min) increased cortical blood flow only pre-ischemically in both models of middle cerebral artery occlusion. gamma 2-MSH had no effect on cortical and striatal infarction volume, while nimodipine caused a significant reduction of cortical infarction volume in the extravasal middle cerebral artery occlusion model. To conclude, despite its hemodynamic and possible neuroprotective properties, gamma 2-MSH did not prevent ischemic neuronal damage after middle cerebral artery occlusion in rats. This might be partly due to the short half-life of the peptide, leading to a transient increase in cortical blood flow and short neuronal exposure time, suggesting that prolonged infusion of the neuropeptide might be required. The results with nimodipine support the notion that it attenuates cortical ischemic damage, independently of effects on cerebral hemodynamics.

Aminoguanidine ameliorates and L-arginine worsens brain damage from intraluminal middle cerebral artery occlusion

BACKGROUND AND PURPOSE

We studied whether the inducible nitric oxide synthase (iNOS) inhibitor aminoguanidine reduces focal cerebral ischemic damage in a relatively noninvasive stroke model in which the rat middle cerebral artery (MCA) is occluded using an intravascular filament.

METHODS

In rats anesthetized with halothane, a nylon filament was advanced into the internal carotid artery until its tip occluded the origin of the MCA. The filament was left in place for 2 hours and then withdrawn. Twenty-four hours later, rats received intraperitoneal injections of aminoguanidine (100 mg/kg BID; n = 7), aminoguanidine+L-arginine (300 mg/kg QID; n = 7), L-arginine alone (n = 6), D-arginine alone (n = 6), or vehicle (n = 10). Drugs were administered for 3 consecutive days. Infarct volume was determined by image analysis in thionin-stained brain sections 4 days after ischemia. iNOS mRNA was detected with the use of reverse transcription polymerase chain reaction.

RESULTS

Cerebral ischemia led to iNOS mRNA expression in the affected brain 48 hours after induction of ischemia. Administration of aminoguanidine reduced neocortical infarct volume by 26% (P < .05 versus vehicle, ANOVA and Tukey's test), a reduction that was antagonized by coadministration of L-arginine (P > .05 versus vehicle). Administration of L-arginine alone, but not D-arginine, enlarged the infarct by 29% (P < .05). Aminoguanidine or L-arginine did not influence the increase in water content in the postischemic brain, indicating that the effect on infarct volume is not related to modulation of ischemic edema.

CONCLUSIONS

These results demonstrate that cerebral ischemia is also associated with iNOS expression in a minimally invasive model of transient MCA occlusion and that iNOS inhibition reduces focal ischemic damage. The findings support the hypothesis that nitric oxide produced by iNOS contributes to ischemic brain damage and that inhibition of iNOS may be a valuable tool in the management of cerebral ischemia.

Brain oxygen, CO2, pH, and temperature monitoring: evaluation in the feline brain

Currently, no ideal method exists for monitoring the injured brain. Recently, a single, compact, fiberoptic sensor has become available for measuring oxygen, CO2, pH and temperature in blood. We have adapted this instrument for continuous use in brain tissue to measure oxygen tension, carbon dioxide tension (pCO2), pH, and temperature. To evaluate this new technique, we produced hypercapnia, hypocapnia, intracranial pressure increase, and hypoxemia in seven normal cats. In an additional six animals, sensors were placed within a zone of focal brain ischemia induced by occluding the left middle cerebral artery. The sensor readings were compared with cerebral blood flow measurements, intracranial pressure, and brain histological findings. An in vitro experiment was also performed using human blood to test the accuracy of the sensor over a wide range of pCO2 and oxygen tension values. After careful precalibration and rigid cranium fixation, stable measurements could be obtained throughout the 6- to 8-hour experiments. In normal animals, brain oxygen was 42 +/- 9 mm Hg, brain CO2 was 59 +/- 14 mm Hg, brain pH was 7.0 +/- 0.2, and brain temperature was 36.7 +/- 0.7 degrees C. Hypocapnia and hypoxemia produced a significant decline in tissue oxygen (< or = 30 +/- 3 mm Hg; P < 0.001), whereas hypercapnia caused by hypoventilation and intracranial pressure increase produced a significant increase in tissue CO2 (> or = 74 +/- 4 mm Hg; P < 0.001). Focal ischemia produced a rapid 42% decline in brain oxygen (25 +/- 7 mm Hg) and a 25% increase in tissue pCO2 (71 +/- 23 mm Hg). Brain oxygen further decreased to 19 +/- 6 mm Hg toward the end of the experiment, 4 hours later. After middle cerebral artery occlusion, the regional cerebral blood flow decreased to 10 +/- 5 ml per 100 g per minute, within the 1st hour, from a baseline value of 65 +/- 15 ml per 100 g per minute. It then gradually increased to 15 +/- 5 ml per 100 g per minute by the end of the 4-hour experiment. Brain pH was closely and inversely related to brain CO2. The brain temperature in the focally ischemic tissue decreased from 36.7 +/- 0.7 to 35.5 +/- 1.6 degrees C by the end of the experiment. The in vitro experiment demonstrated good linear correlation between the sensor readings and the blood gas analysis. Continuous monitoring of oxygen, CO2, pH, and temperature in damaged or at-risk brain tissue using a single sensor is now feasible and will, thus, allow improved continuous monitoring of neurosurgical patients who are at risk of significant secondary brain damage.

HU-211, a novel noncompetitive N-methyl-D-aspartate antagonist, improves neurological deficit and reduces infarct volume after reversible focal cerebral ischemia in the rat

BACKGROUND AND PURPOSE

HU-211 is a nonpsychotropic cannabinoid analogue that has been shown to act as a functional N-methyl-D-aspartate receptor blocker. We investigated the neuroprotective efficacy of HU-211 in a model of reversible middle cerebral artery occlusion (MCAo) in rats.

METHODS

Male Wistar rats were anesthetized with halothane and subjected to 90 minutes of temporary MCAo by retrograde insertion of an intraluminal nylon suture, coated with poly-L-lysine, through the external carotid artery into the internal carotid artery and MCA. The drug (HU-211 in cosolvent, 4 mg/kg IV) or vehicle was administered in a blinded fashion 70 minutes after onset of MCAo. Behavioral tests were evaluated during occlusion (60 minutes) and for a 3-day period after MCAo. Three days after MCAo, brains were perfusion-fixed, and infarct volumes were determined.

RESULTS

HU-211 significantly improved the neurological score compared with vehicle during the 3 days after MCAo. Treatment with HU-211 also significantly reduced both infarct volume (mean +/- SEM, 66.6 +/- 12.5 versus 149.8 +/- 36.3 mm3) and brain swelling (2.61 +/- 1.33% versus 6.66 +/- 1.24%) compared with vehicle-treated rats (n = 17 in each group).

CONCLUSIONS

These results demonstrate the neuroprotective ability of HU-211 in focal cerebral ischemia as judged by neurological score, infarct size, and brain swelling. Reversible MCAo with the use of a poly-L-lysine-coated intraluminal suture proved to be a reliable and effective modification of this technique, yielding consistent results.

The neuroprotective effect of chlormethiazole on ischaemic neuronal damage following permanent middle cerebral artery ischaemia in the rat

The ability of chlormethiazole to protect against ischaemic cell damage in a rat model of permanent focal ischaemia has been examined. Chlormethiazole (1 mmol/kg) was administered intraperitoneally either 1 or 3 h after occlusion of the middle cerebral artery with an intraluminal filament. Twenty four hours after the start of occlusion there was histological evidence for ischaemic damage in both cortex and striatum. The volume of ischaemic damage in control (saline injected) animals was 310 +/- 25 mm3 (mean +/- SEM; n = 6). Chlormethiazole administered 1 h after occlusion reduced this damage by 58% (128 +/- 40 mm3; n = 6; P < 0.01), protection being observed in both brain regions. The drug was ineffective when given 3 h after occlusion (304 +/- 25 mm3; n = 5). Chlormethiazole had no effect on body temperature, mean arterial blood pressure, blood pH, pO2 or pCO2, but did induce mild bradycardia. Chlormethiazole therefore appears to be an effective neuroprotective agent in this model of permanent ischaemia, complementing previous data on the efficacy of this drug in other focal and global models of cerebral ischaemia.

N-tert-butyl-alpha-phenylnitrone improves recovery of brain energy state in rats following transient focal ischemia

Recent results have demonstrated that the spin trapping agent N-tert-butyl-alpha-phenylnitrone (PBN) reduces infarct size due to middle cerebral artery occlusion (MCAO), even when given after ischemia. The objective of the present study was to explore whether PBN influences recovery of energy metabolism. MCAO of 2-hr duration was induced in rats by an intraluminal filament technique. Brains were frozen in situ at the end of ischemia and after 1, 2, and 4 hr of recirculation. PBN was given 1 hr after recirculation. Neocortical focal and perifocal ("penumbra") areas were sampled for analyses of phosphocreatine (PCr), creatine, ATP, ADP, AMP, glycogen, glucose, and lactate. The penumbra showed a moderate-to-marked decrease and the focus showed a marked decrease in PCr and ATP concentrations, a decline in the sum of adenine nucleotides, near-depletion of glycogen, and an increase in lactate concentration after 2 hr of ischemia. Recirculation for 1 hr led to only a partial recovery of energy state, with little further improvement after 2 hr and signs of secondary deterioration after 4 hr, particularly in the focus. After 4 hr of recirculation, PBN-treated animals showed pronounced recovery of energy state, with ATP and lactate contents in both focus and penumbra approaching normal values. Although an effect of PBN on mitochondria cannot be excluded, the results suggest that PBN acts by preventing a gradual compromise of microcirculation. The results justify a reevaluation of current views on the pathophysiology of focal ischemic damage and suggest that a therapeutic window of many hours exists in stroke.

Hyperthermia nullifies the ameliorating effect of dizocilpine maleate (MK-801) in focal cerebral ischemia

The present study was inspired by two previous findings from the laboratory. The first was that dizocilpine maleate (MK-801) fails to reduce infarct size when the middle cerebral artery (MCA) is permanently occluded by an intraluminal filament technique in rats. In seeking the reasons for this we measured temperature and found that the body temperature of occluded animals increases to 39.0-39.5 degrees C during the first 2-3 h. In order to explore whether the rise in temperature was responsible for the lack of effect of MK-801, two groups of animals were studied, both containing animals which were subjected to 2 h of transient MCA occlusion and given MK-801 15 min before, as well as 6 and 24 h after ischemia. In one group, temperature was allowed to rise spontaneously during ischemia (39.0-39.5 degrees C). In the other, body temperature was maintained close to normal during ischemia, and for the first 6 h postischemically, by cooling of the ambient air. Infarct volume was assessed by triphenyltetrazolium chloride staining after 48 h of recovery. The results showed that MK-801 failed to reduce infarct size in animals whose body temperature rose during ischemia. In contrast, the drug markedly reduced infarct volume in temperature-controlled animals; in fact, 5/8 animals had no infarcts but selective neuronal damage only. The results suggest that amelioration of focal ischemic damage cannot be expected if body and brain temperature is allowed to rise above normal.

Preischemic hyperglycemia leads to delayed postischemic hyperthermia

BACKGROUND AND PURPOSE

Temperature alterations are known to influence the outcome of transient ischemia, even when instituted in the postischemic period. Since preischemic hyperglycemia aggravates ischemic brain damage, the question of whether hyperglycemic animals become hyperthermic arose. To explore this possibility, we measured body temperature telemetrically in normoglycemic and hyperglycemic rats subjected to 10 minutes of forebrain ischemia at a body (and brain) temperature of 37 degrees C.

METHODS

Isoflurane-anesthetized animals were subjected to 10 minutes of forebrain ischemia under normoglycemic or hyperglycemic conditions. Temperature changes after ischemia were measured by means of a telemetric temperature coil.

RESULTS

In normoglycemic animals, temperature decreased to 35.6 +/- 1.1 degrees C (mean +/- SD) during the first 4 hours of recovery, after which it gradually increased to normal values (38 degrees C). Hyperglycemic animals behaved differently in that they remained normothermic for approximately 10 hours during recovery and later became hyperthermic, with core temperatures rising above 39 degrees C. The rise in temperature was not due to the osmotic load of the glucose administered because infusion of mannitol, which gave a comparable increase in plasma osmolality, failed to cause delayed postischemic hyperthermia. Excessive hypercapnia during ischemia in normoglycemic animals, which produces cerebral acidosis of a magnitude similar to that of hyperglycemia and is known to aggravate ischemic lesions, likewise failed to induce hyperthermia. When post-ischemic seizures ensued in hyperglycemic subjects, temperature was 39.8 +/- 0.6 degrees C. Animals with seizures invariably died. To evaluate the influence of postischemic hyperthermia on the outcome, an additional series of experiments was performed in which delayed hyperthermia was avoided by gentle cooling (n = 6) or by acetaminophen administration (n = 5). Although these procedures prevented delayed hyperthermia, they neither blocked seizure induction nor affected the fatal outcome. Postischemic seizures developed when the core temperatures of animals were 37.9 +/- 0.1 degrees C and 37.8 +/- 0.2 degrees C in the cooled and acetaminophen-treated groups, respectively.

CONCLUSIONS

The results suggest that both delayed hyperthermia and delayed seizures in hyperglycemic animals are caused by the aggravated damage incurred by these animals during or immediately after the ischemic insult.