Immediate effects of cerebral ischemia: evolution and resolution of neurological deficits after experimental occlusion of one middle cerebral artery in conscious cats

Prospects of modeling poststroke epileptogenesis

This Review describes the current status of poststroke epilepsy (PSE) with an emphasis on poststroke epileptogenesis modeling for testing new therapeutic agents. Stroke is a leading cause of epilepsy in an aging population. Late-onset "epileptic" seizures have been reported in up to 30% cases after stroke. Nevertheless, the overall prevalence of PSE is 2-4%. Rodent models of stroke have contributed to our understanding of the relationship between seizures and the underlying ischemic damage to neurons. To understand whether acutely generated stroke events lead to a chronic phenotype more closely resembling PSE with recurrent seizures, a limited variety of approaches emerged in early 2000s. These limited methods of causing an occlusion in mice and rats show different infarct size and neurological deficits. The most often employed procedure for inducing focal ischemia is the middle cerebral artery occlusion. This mimics the pathophysiology seen in humans in terms of extent of damage to cortex and striatum. Photothrombosis and endothelin-1 models can similarly evoke episodes of ischemic stroke. These models are well suited to studying mechanisms and biomarkers of epileptogenesis or optimizing novel drug discoveries. However, modeling of PSE is tedious, is highly variable, and lacks validity; therefore, it is not widely implemented in epilepsy research. Moreover, the relevance of ischemic models to specific forms of human stroke remains unclear. Stroke modeling in young male rodents lacks clinical relevance to elderly populations and especially to women, likely as a result of sex differences. Nevertheless, because of the neuronal damage and epileptogenic insult that these models trigger, they are helpful tools in studying acquired epilepsy and prophylactic drug therapy. © 2016 Wiley Periodicals, Inc.

Large animal canine endovascular ischemic stroke models: A review

BACKGROUND

Stroke is one of the leading causes of death and long-term disability worldwide. Recent exciting developments in the field with endovascular treatments have shown excellent outcomes in acute ischemic stroke. Prior to translating these treatments to human populations, a large-animal ischemic stroke model is needed. With the advent of new technologies in digital subtraction angiography, less invasive endovascular stroke models have been developed. Canines have gyrencephalic brain similar to human brain and accessible neurovascular anatomy for stroke model creation. Canine stroke model can be widely utilized to understand the disease process of stroke and to develop novel treatment. Less invasive endovascular internal carotid emboli injection and coil embolization methods can be used to simulate transient or permanent middle cerebral artery occlusion. Major restriction includes the extensive collateral circulation of canine cerebral arteries that can limit the stroke size. Transient internal carotid artery occlusion can decrease collateral circulation and increase stroke size to some degree. Additional method of manipulating the extent of collateral circulation needs to be studied. Other types of canine stroke models, including vertebral artery occlusion and basilar artery occlusion, can also be accomplished by endovascular thrombi injection.

CONCLUSIONS

We extensively review the literature on endovascular technique of creating canine ischemic stroke models and their application in finding new therapies for ischemic stroke.

Neuroprotective effect of olive oil in the hippocampus CA1 neurons following ischemia: Reperfusion in mice

INTRODUCTION

Transient global ischemia induces selective, delayed neuronal death of pyramidal neurons in the hippocampal CA1. Oxidative Stress is considered to be involved in a number of human diseases including ischemia. Preliminary studies confirmed reduction of cell death in brain following treatment with antioxidants.

AIM

According to this finding, we study the relationship between consumption of olive oil on cell death and memory disorder in brain ischemia. We studied the protective effect of olive oil against ischemia-reperfusion.

MATERIAL AND METHODS

EXPERIMENTAL DESIGN INCLUDES THREE GROUPS: Intact (n = 8), ischemic control (n = 8) and treatment groups with olive oil (n = 8). The mice treated with olive oil as pre-treatment for a week. Then, ischemia induced by common carotid artery ligation and following the reduction of inflammation [a week after ischemia], the mice post-treated with olive oil. Nissl staining applied for counting necrotic cells in hippocampus CA1. Tunnel kit was used to quantify apoptotic cell death while to short term memory scale, we apply y-maze and shuttle box tests and for detection the rate of apoptotic and treated cell, we used western blotting test for bax and bcl2 proteins.

RESULTS

High rate of apoptosis was seen in ischemic group that significantly associated with short-term memory loss. Cell death was significantly lower when mice treated with olive oil. The memory test results were adjusted with cell death results and bax and bcl2 expression in all groups' comparison. Ischemia for 15 min induced cell death in hippocampus with more potent effect on CA1.

CONCLUSION

Olive oil intake significantly reduced cell death and decreased memory loss.

Biosensors for brain trauma and dual laser doppler flowmetry: enoxaparin simultaneously reduces stroke-induced dopamine and blood flow while enhancing serotonin and blood flow in motor neurons of brain, in vivo

Neuromolecular Imaging (NMI) based on adsorptive electrochemistry, combined with Dual Laser Doppler Flowmetry (LDF) is presented herein to investigate the brain neurochemistry affected by enoxaparin (Lovenox(®)), an antiplatelet/antithrombotic medication for stroke victims. NMI with miniature biosensors enables neurotransmitter and neuropeptide (NT) imaging; each NT is imaged with a response time in milliseconds. A semiderivative electronic reduction circuit images several NT's selectively and separately within a response time of minutes. Spatial resolution of NMI biosensors is in the range of nanomicrons and electrochemically-induced current ranges are in pico- and nano-amperes. Simultaneously with NMI, the LDF technology presented herein operates on line by illuminating the living brain, in this example, in dorso-striatal neuroanatomic substrates via a laser sensor with low power laser light containing optical fiber light guides. NMI biotechnology with BRODERICK PROBE(®) biosensors has a distinct advantage over conventional electrochemical methodologies both in novelty of biosensor formulations and on-line imaging capabilities in the biosensor field. NMI with unique biocompatible biosensors precisely images NT in the body, blood and brain of animals and humans using characteristic experimentally derived half-wave potentials driven by oxidative electron transfer. Enoxaparin is a first line clinical treatment prescribed to halt the progression of acute ischemic stroke (AIS). In the present studies, BRODERICK PROBE(®) laurate biosensors and LDF laser sensors are placed in dorsal striatum (DStr) dopaminergic motor neurons in basal ganglia of brain in living animals; basal ganglia influence movement disorders such as those correlated with AIS. The purpose of these studies is to understand what is happening in brain neurochemistry and cerebral blood perfusion after causal AIS by middle cerebral artery occlusion in vivo as well as to understand consequent enoxaparin and reperfusion effects actually while enoxaparin is inhibiting blood clots to alleviate AIS symptomatology. This research is directly correlated with the medical and clinical needs of stroke victims. The data are clinically relevant, not only to movement dysfunction but also to the depressive mood that stroke patients often endure. These are the first studies to image brain neurotransmitters while any stroke medications, such as anti-platelet/anti-thrombotic and/or anti-glycoprotein are working in organ systems to alleviate the debilitating consequences of brain trauma and stroke/brain attacks.

Checkpoints and pitfalls in the experimental neuropathology of circulatory disturbance

In neural tissue injury many pathological processes are common to different neurological disorders, including cerebral ischemia. Because ischemia has a fundamentally simple impact on neural tissue, good laboratory modeling can help improve the general understanding of the neuropathological processes involved. Summarized here are some basic principles that should be followed to ensure that cerebral ischemia studies are reproducible and informative: (i) selection of an appropriate model of cerebral ischemia in an appropriate species (although rodents are widely used for genomic studies, the use of larger animals, with brain structures macroscopically similar to those of humans, is appropriate for many studies, e.g. of white matter lesions or the pathophysiology of cerebral edema); (ii) correct maintenance of physiological parameters, including body temperature, systemic blood pressure, and blood gas tensions, under appropriate general anesthesia; (iii) selection of an appropriate method of cerebral blood flow (CBF) monitoring (decisions include whether or not the experiment requires real-time monitoring, in vivo measurement, and CBF mapping); (iv) appropriate timing of drug application in therapeutic studies (many drugs that are effective when given immediately after a short period of ischemia are ineffective in clinical trials, probably because of longer periods of ischemia and delayed drug delivery in clinical settings); and (v) multiparametric evaluation of therapeutic effect (with the recent increase in diagnosis of cases of mild stroke, measurement of mortality and infarct size have proven to be insufficient for the evaluation of therapeutic effect). Use of mild ischemia models and batteries of neurological tests for individual neurological functions, such as motor, somatosensory, and visual function, are becoming important in experimental ischemia research. In histological evaluation, assessment of the extent of both selective neuronal loss and the infarct will become mandatory. Regional analysis of each brain structure and coordination of the results with the apparent neurological dysfunction is a promising approach.

Effect of JTP-2942, a novel thyrotropin-releasing hormone analog, on motor deficits after chronic focal cerebral ischemia in rats

To investigate the chronic effects of a novel thyrotropin-releasing hormone analog, JTP-2942 (N(alpha)-[(1S, 2R)-2-methyl-4-oxocyclopentylcarbonyl]-L-histidyl-L-prolinamide monohydrate), on behavioral changes after stroke, the authors examined its effects on motor and neurologic deficits using a middle cerebral artery (MCA) occlusion model in rats. A left MCA was permanently occluded at a proximal site. From 1 week after occlusion, JTP-2942 was intravenously administered once a day for 4 weeks. Sensorimotor performance was evaluated weekly for 10 weeks after the occlusion. The ability of the rat to maintain its body position on an inclined plane and neurologic examination based on hemiparesis and abnormal posture were examined. After all behavioral examinations were completed, the degree of shrinkage of the left hemisphere was measured. The ability of MCA-occluded rats to maintain body position on an inclined plane in the left-headed position was significantly lower than that of sham-operated rats throughout the test period. JTP-2942 gradually improved this deficit dose dependently, and a dose of 0.03 mg/kg of JTP-2942 significantly improved performance to the levels of the sham-operated rats. Neurologic deficits were also observed in MCA-occluded rats. JTP-2942 also significantly improved these deficits dose dependently. On the other hand, CDP-choline (500 mg/kg, administered intravenously), a therapeutic agent for the disturbance of consciousness and hemiparesis after stroke, improved neurologic deficits but did not affect the motor deficits measured using the inclined plane. It is noteworthy that the effects of JTP-2942 on these deficits were observed 4 weeks after cessation of drug administration. Furthermore, there was no difference in the degree of shrinkage of the cerebrum among the MCA-occluded groups. In the present study, long-lasting improving effects of JTP-2942 on the impairment of motor and neurologic functions were observed in rats with MCA occlusion, which continued after cessation of drug administration and which were not attributable to a reduction in ipsilateral cerebral shrinkage. It is considered that the effect of JTP-2942 on functional recovery is attributable to the activation of substitutive functions such as neuronal reconstruction. These pharmacologic properties of JTP-2942 may be of interest for the treatment of patients with motor and neurologic deficits during the chronic or subacute phase of stroke.

Behavioral changes after focal cerebral ischemia by left middle cerebral artery occlusion in rats

Behavioral changes after occlusion of the left middle cerebral artery (MCA) in rats were investigated for 16 weeks. Impairment of motor coordination and incidence of neurological deficits including hemiplegia and abnormal posture were present for the first 2 and 4 weeks after MCA occlusion, respectively. Learning behavior in one-trial passive avoidance task was disturbed for the entire 16-week period when rats were trained at days 3 after MCA occlusion. Reacquisition was also impaired when rats were retrained on 8 weeks after MCA occlusion. Except for synchronized EEG at days 2 after MCA occlusion, significant changes in spontaneous movement and EEG were not observed in the MCA-occluded group. These results suggest that this rat model of MCA-occlusion is useful for quantitatively measuring functional changes in chronic phase of focal cerebral ischemia.

Cerebral energy metabolism measured in vivo by 31P-NMR in middle cerebral artery occlusion in the cat--relation to severity of stroke

The energy metabolism of the brain has been measured in a middle cerebral artery (MCA) occlusion model in the cat utilizing 31P-nuclear magnetic resonance (NMR). 31P-NMR spectra were serially obtained during 2 h of ischemia and a subsequent 4-h recovery period. The ratio of creatine phosphate (PCr) to inorganic phosphate (Pi) (PCr/Pi) showed a precipitous decrease in parallel with changes in electroencephalographic (EEG) amplitude in severe strokes during ischemia as well as during recirculation. Animals with mild strokes, as determined by EEG criteria, exhibited a much smaller decrease in PCr/Pi during ischemia. In the severe strokes, there was a splitting and significant shift of the Pi peak immediately after occlusion. In addition, the shifted Pi peak rapidly increased and remained elevated throughout the study. In the mild strokes, Pi also increased, but not as markedly. Intracellular pH determination by chemical shift of the Pi peak revealed a decrease from 7.1 to 6.2-6.3 during ischemia and the subsequent recovery period in the animals with severe strokes, whereas the pH in the animals with mild strokes did not show a significant change. A gradual decrease in adenosine triphosphate (ATP) to 57-79% of the control was exhibited in severely stroked animals during both the ischemia and the recovery period, whereas there was no change in ATP in the mild stroked animals. These results suggest that the dynamic process of pathophysiological changes in an MCA occlusion model in the cat leads to significant differences in cerebral metabolism between animals with mild and severe strokes.

Cortical deafferentation in cat focal ischemia: disturbance and recovery of sensory functions in cortical areas with different degrees of cerebral blood flow reduction

During and after 15-min occlusion of the middle cerebral artery (MCA) in cats, local CBF and neuronal activity were measured in cortical areas varying in the degree of CBF reduction. In an area within the ischemic center (primary auditory cortex, middle ectosylvian gyrus), CBF was severely suppressed. Click-induced auditory evoked potentials and evoked as well as spontaneous single-unit activity ceased within 1 min after occlusion. Recirculation resulted in a recovery of the different neurophysiological parameters with a time delay ranging from several minutes to 2 h. In two areas surrounding the ischemic focus (a visual area in the marginal gyrus and the forelimb representation area in the primary somatosensory cortex), CBF was reduced but remained above 30 ml/100 g/min during MCA occlusion. Visual flash-induced evoked potentials and somatosensory evoked potentials induced by median nerve electrical stimulation ceased in the corresponding areas with a somewhat slower time course as compared to the auditory responses and they recovered faster after recirculation. In another somatosensory area (hindlimb projection area in the primary somatosensory cortex), CBF stayed nearly at control levels during occlusion. Evoked potentials and single-unit activity induced by tibial nerve electrical stimulation decreased approximately 5 min after occlusion and were abolished approximately 5 min later. At that time, single-unit activity had changed to a nonresponsive pattern but persisted. However, potentials evoked transcallosally by electrical stimulation of the contralateral hemisphere were still recorded. After reopening the MCA, the recovery of neuronal functions was usually complete and occurred within approximately 5 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the effect of fluosol DA and dextran 40 on regional cerebral blood flow, infarction size, and mortality in cats with temporary occlusion of the middle cerebral artery

Twenty-four cats were divided into two groups and treated with an intravenous infusion of either fluosol DA or dextran. One-half of the animals in each group were ventilated with room air and one-half with 100% oxygen. The right middle cerebral artery was occluded for a period of 4 hours through a transorbital approach. Regional blood flow by the hydrogen clearance method was measured before and after the infusion of fluosol DA or dextran, after oxygenation in the animals on 100% oxygen, three times during the period of ischemia, and after reperfusion. Regional cerebral blood flow increased slightly with the infusion of fluosol or dextran, decreased slightly with hyperoxygenation in the animals so treated, and decreased markedly in the right hemisphere during temporary occlusion of the right middle cerebral artery in all groups. With reperfusion regional flows in the right hemisphere varied considerably, with some animals showing hyperperfusion and others essentially no flow. There was no significant difference in average regional cerebral blood flow between any of the groups. The severity of infarction in all groups was directly related to the decrease in regional cerebral blood flow in the right hemisphere during temporary occlusion. There was also a strong correlation between the regional cerebral blood flow in the right hemisphere after reperfusion and the severity of infarction. In general, the animals showing normal or increased flow after reperfusion had small infarcts and those showing no reflow had large infarcts. Mortality was high in all groups, was not significantly different between any of the groups, and was highly correlated to the size of infarction. In brief, in this study fluosol offered no advantage over dextran, and probably neither agent, in the dose used, offered any protection against cerebral ischemia.

A prophylactic bolus of thiopentone does not protect against prolonged focal cerebral ischaemia

Barbiturate coma is still recommended for brain protection during periods of temporary focal ischaemia such as during carotid endarterectomy. We tested the hypothesis that a single dose of barbiturate given before a period of protracted severe focal ischaemia would protect against focal cerebral infarction. Sixteen cats had the proximal left middle cerebral artery (MCA) occluded. Eight cats received halothane alone titrated to keep their pulse and blood pressure within the normal range. Eight cats received, in addition to halothane, a bolus of thiopentone sufficient to produce an isoelectric EEG immediately prior to MCA occlusion. Six hours after the occlusions the animals were sacrificed and the brains scored histologically to assess both size and severity of ischaemia. There was no statistically significant difference in the size or severity of the infarcts between the groups. We conclude from this study that the extent of the histological injury was not reduced by a single prophylactic bolus of thiopentone given before prolonged focal cerebral ischaemia.

An unanesthetized-gerbil model of cerebral ischemia-induced behavioral changes

A surgical procedure has been developed to study the effects of cerebral ischemia in the unanesthetized Mongolian gerbil. The methodology is based upon the surgical isolation and instrumentation of both common carotid arteries. A loop of dental floss is placed around each carotid artery and passed through double lumen catheter material; this allows for later occlusion of the carotid arteries and their release in unanesthetized subjects. Functional changes following transient carotid artery occlusion are readily demonstrated by the occurrence of altered spontaneous locomotor activity at various times postischemia. This model should be useful in the evaluation of potential therapeutic agents in the treatment of cerebral ischemia.

Neurologic deficit, blood flow and biochemical sequelae of reversible focal cerebral ischemia in cats

Temporary focal cerebral ischemia was induced in 23 cats by occluding the left middle cerebral artery (MCA) for 2 h. Animals then were divided into groups for unforced reperfusion of varying duration ranging from 2 to 48 h. Regional blood flow (rCBF) at the borders of the ischemic area was measured repeatedly using the hydrogen clearance technique, and neurological ratings were obtained, both during ischemia and reperfusion. At the scheduled end of reperfusion brains were frozen in situ with liquid nitrogen, and regional distributions of biochemical substrate contents as well as tissue pH were visualized using bioluminescence and fluorescence techniques. During focal ischemia collateral flow in the border zone dropped to 55 +/- 20.3% of control level, and all animals developed a neurologic deficit with a median of 6 points on a disability scale from 0 to 10, rCBF and functional impairment being closely correlated (tau = -0.47, P1 less than 0.005). After reopening of the MCA there was an immediate and rather uniform increase in border zone flow to 105 +/- 25.7% of control level, while neurologic recovery was quite variable. In all but one animal reversible ischemia led to persistent disturbances in the energy-producing metabolism as demonstrated by the low regional ATP content, which in part was accompanied by a diminished NADH fluorescence and an alkaline pH shift at high tissue glucose levels. These findings suggest that disturbances in cerebral energy metabolism induced by temporary ischemia may be caused by inhibition of the glycolytic pathway that is hardly reversed by unforced reperfusion and, therefore, results in permanent damage.

Neurologic deficit and cerebral ATP depletion after temporary focal ischemia in cats

Focal ischemia was induced in 23 cats by occluding the left middle cerebral artery for 2 h. The animals were then divided into groups for unforced reperfusion of variable duration ranging from 2 to 48 h. Neurological ratings were obtained during both ischemia and reperfusion. Following planned sacrifice the regional ATP content was assessed by means of a bioluminescence method showing spatial distribution and degree of ATP depletion. All the animals developed a neurologic deficit, with a median of 6 points on a disability scale of 0-10. After reopening of the middle cerebral artery, neurologic recovery was quite variable depending on the initial neurologic deficit (partial phi = 0.67, p1 less than 0.05): Animals with mild initial functional impairment improved and those with severe neurologic disturbances either died early or developed a more severe neurologic deficit, irrespective of the duration of reperfusion. The degree of ATP depletion and the amount of brain tissue involved exhibited a significant correlation with the neurological outcome (tau = 0.50, p1 less than 0.05), but they were even more closely related to the initial neurologic deficit (partial phi = 1.00, p1 less than 0.001), suggesting an early definitive manifestation of deficiencies in regional energy metabolism.

Functional recovery of cortical neurons as related to degree and duration of ischemia

Simultaneous recordings of spontaneous single cell activity and local cerebral blood flow were obtained from 72 cortical neurons and adjacent brain in 54 cats before, during, and after ischemia induced by reversible occlusion of the middle cerebral artery. In most cells spontaneous electrical activity ceased at flow values of about 0.18 ml/gm/min (range, 0.06 to 0.22 ml/gm/min). No signal was obtained from 28 neurons during reperfusion following ischemia of varying degree and duration. Overall, neurons exposed to a residual flow of 0.14 ml/gm/min or less for more than 45 minutes had a poorer prognosis compared to any other combination of degree and duration of ischemia. A discriminant curve was estimated to define the border line between recovering and nonrecovering cells. Regions showing irreversible neuronal failure contained selective neuronal necrosis or areas of infarction by histological examination. Reperfusion restored neuronal function in 44 cells. In this group of neurons, there was a joint interaction of duration of ischemia, ischemic residual flow, and recovery time: cells exposed to moderate ischemia (0.09 to 0.22 ml/gm/min) for up to 20 minutes recovered rapidly; most neurons subjected either to extreme ischemia (less than 0.09 ml/gm/min) of short duration (less than 20 minutes) or to moderate ischemia (0.09 to 0.22 ml/gm/min) for longer periods (20 to 141 minutes) required from 19 to 50 minutes for recovery. A few resistant neurons tolerated less than 0.09 ml/gm/min for more than 20 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure of naloxone to affect focal incomplete cerebral ischemia and collateral blood flow in cats

Focal incomplete cerebral ischemia was created in 20 adult cats by retro-orbital middle cerebral artery (MCA) occlusion under halothane anesthesia. Arterial blood flow (CBF), bilateral electroencephalographic (EEG) recordings, and systemic arterial blood pressure (SABP) were monitored for the 1st hour of occlusion. Ten animals were treated with 10 mg/kg of naloxone within 10 minutes of MCA clipping, followed by a continuous infusion of naloxone at 2 mg/kg/hr for the duration of the occlusion (8 hours). Ten animals were treated in a similar fashion with physiological saline (control). Blood flow was restored after 8 hours. The brains were examined at the time of death or 7 days after the occlusion period. There was no difference between the two groups regarding cerebral infarction size or distribution, neurological outcome, SABP, PaCO2, or CBF. Minor changes in EEG amplitude observed in the naloxone-treated group appear to represent interaction of the drug with halothane after prolonged administration. The authors conclude that naloxone did not modify the outcome of focal cerebral ischemia in the cat.

Comparison of middle cerebral artery trunk occlusion by silicone cylinder embolization and by trapping

The authors produced occlusion of the middle cerebral artery (MCA) trunk in dogs by two methods: silicone cylinder embolization and trapping. Comparative analyses of the clinicopathological features in these models, extending from the acute to chronic stage, were performed. Within 24 hours after embolization, the brain exhibited swelling without macroscopic infarction. Microangiograms revealed impaired filling in the deep areas of the brain with midline shift. At 4 to 7 days after embolization, the animals showed major neurological deficits, evident deep cerebral infarction, and poorly perfused areas in the deep cerebrum with prominent midline shift. At 3 to 4 weeks after embolization, the neurological deficits improved and the affected regions showed cavities or localized lesions. Microangiograms demonstrated hypervascular areas with abnormal vessels in the affected cerebrum. On the other hand, trapping of the MCA trunk produced mild neurological deficits, although there was no evidence of macroscopic lesions or impairment of filling. This study shows that silicone cylinder embolization in the MCA trunk produces a reliable and reproducible deep cerebral infarction in dogs.

Omental transposition or transplantation to the brain and superficial temporal artery--middle cerebral artery anastomosis in preventing experimental cerebral ischaemia

Transposition of lengthened omentum to the brain surface, transplantation of an omental graft, or superficial temporal artery--middle cerebral artery anastomosis were performed in dogs prior to transcranial occlusion of the ipsilateral middle cerebral artery at its origin, including the bifurcation of the internal carotid artery. Both omentum and by-pass were able to reduce the changes in cerebral blood flow, somatosensory evoked responses, cerebral water and electrolyte content, consequent to the ischaemic insult. In the experimental conditions adopted in this study, the effect of omental transposition in maintaining high levels of flow throughout the entire occluded hemisphere was more marked compared to that resulting from the other methods, while the onset of ischaemic cerebral oedema was affected approximately at the same degree by all procedures. The results point to the role of the transposed omentum in providing an effective collateral circulation to the ischaemic brain.

Thresholds of focal cerebral ischemia in awake monkeys

An awake-primate model has been developed which permits reversible middle cerebral artery (MCA) occlusion during physiological monitoring. This method eliminates the ischemia-modifying effects of anesthesia, and permits correlation of neurological function with cerebral blood flow (CBF) and neuropathology. The model was used to assess the brain's tolerance to focal cerebral ischemia. The MCA was occluded for 15 or 30 minutes, 2 to 3 hours, or permanently. Serial monitoring evaluated neurological function, local CBF (hydrogen clearance), and other physiological parameters (blood pressure, blood gases, and intracranial pressure). After 2 weeks, neuropathological evaluation identified infarcts and their relation to blood flow recording sites. Middle cerebral artery occlusion usually caused substantial decreases in local CBF. Variable reduction in flow correlated directly with the variable severity of deficit. Release of occlusion at up to 3 hours led to clinical improvement. Pathological examination showed microscopic foci of infarction after 15 to 30 minutes of ischemia, moderate to large infarcts after 2 to 3 hours of ischemia, and in most cases large infarcts after permanent MCA occlusion. Local CBF appeared to define thresholds for paralysis and infarction. When local flow dropped below about 23 cc/100 gm/min, reversible paralysis occurred. When local flow fell below 10 to 12 cc/100 gm/min for 2 to 3 hours or below 17 to 18 cc/100 gm/min during permanent occlusion, irreversible local damage was observed. These studies imply that some cases of acute hemiplegia, with blood flow in the paralysis range, might be improved by surgical revascularization. Studies of local CBF might help identify suitable cases for emergency revascularization.

Experimental cerebral infarction in primates: regional changes in brain histamine content

Histamine levels in different regions of the brain in the primate Macaca Radiata were studied following experimental infarction induced in the basal ganglia by coagulation of the middle cerebral artery. In the basal ganglia an elevation of histamine level was seen probably due to proliferation of mast cells. In the hypothalamus, a main constituent of the ascending histaminergic neuronal pathway, a sharp rise in histamine content occurred in infarcted as well as sham-operated animals: this probably reflects non-specific stress-related alterations. In contrast, the cortical area of the ischemic hemisphere showed a higher elevation of histamine, demonstrating that infarction in one region can cause widespread specific changes in histaminergic systems remote from the infarct. The rise in histamine level at the ischemic site could evoke an increase in microcirculation which might aggravate cerebral edema, while changes in the remote regions may be responsible for some of the neurological deficits following stroke.

Regional cortical metabolism in focal ischemia

Regional cortical levels of organic phosphates and carbohydrates were measured in cat brains, enzymatically inactivated by the technique of "funnel freezing" 1 hour after occlusion of a middle cerebral artery (MCA). Significant metabolic alterations occurred in all hemispheres ipsilateral to the site of occlusion. However, there was marked interindividual variability, with changes ranging from only slight increases in lactate, pyruvate, and adenosine monophosphate (AMP) in small regions of cortex at one extreme, to profound depletion of high-energy phosphates, depression of glucose and pyruvate levels, and increased lactate, adenosine diphosphate (ADP) and AMP levels in much of the hemisphere of the most severely involved animals. In contrast, metabolic changes in the hemisphere contralateral to the site of occlusion were very few or nonexistent. In addition, in all ipsilateral hemispheres there were regions peripheral to the areas of greatest metabolic alteration where there was excessive elevation of glucose levels. The results demonstrate that occlusion of a major cerebral vessel does not produce metabolic changes that are consistent in their distribution or severity. However, the findings of this study probably depict some of the complicated metabolic events that occur clinically during thrombotic or embolic infarction of brain.

The protective effects of dietary fish oil on focal cerebral infarction

The protective effect of the (n-3) fatty acids in menhaden fish oil on acute cerebral ischemia was investigated in cats. Cerebral ischemia was produced by ligation of the left middle cerebral artery of cats fed either a basal diet of feline cat chow or the basal diet supplemented with 8% of the calories as menhaden oil for 18-24 days. Fatty acids esters of 20:5 (n-3) were increased and the 18:2 (n-6) decreased in the heart and liver of cats fed supplemental fish oil, but the brain lipid showed no effect of the diet. We found that the neurological deficit and the volume of brain infarction in the group treated with fish oil was less than that of the control group. The present findings suggest that moderate dietary supplements of fish oil may be beneficial in the prophylactic treatment of ischemic cerebral vascular disease.

Acute cerebral revascularization after regional cerebral ischemia in the dog. Part 2: Clinicopathological correlation

The efficacy of cerebral revascularization by anastomosis of the superficial temporal artery (STA) to the middle cerebral artery (MCA), performed 4 and 24 hours after a regional MCA infarction had been produced by combined occlusion of the MCA and internal carotid artery, was tested in 12 dogs. To control possible intercurrent variables, seven other dogs remained untreated and five had a sham operation. Clinical and pathological changes were recorded and analyzed. An incidence of 85% infarction was obtained in the untreated control group. The severity of the clinical deficits and pathological changes for the anastomosed groups were greater than those seen in the untreated control group. The extent of the infarction was significantly greater (p less than 0.05) in the anastomosed groups than in the sham-operated and control groups. Hemorrhagic infarcts occurred in most of the dogs in the anastomosed groups, but were not present in either control group (p less than 0.05). Two dogs in the 4-hour and one in the 24-hour group improved more than any control dog, but the difference was not statistically significant (p greater than 0.05). In two dogs with occluded anastomosis the clinical deficits and the pathological changes were less than those seen in animals with patent anastomosis. The severity of the pathological and clinical changes correlated well with the reestablishment of flow in the MCA territory. It is proposed that cerebral revascularization at 4 and 24 hours following a regional MCA infarct in the dog is followed by an exacerbation of the microcirculatory obstruction, cerebral edema, and infarction. From improvement noted in three animals the authors suggest that under special conditions the revascularization could benefit some cases following acute cerebral infarction.

Modification of acute focal ischemia by treatment with mannitol and high-dose dexamethasone

A simple implanted device was used to occlude the left middle cerebral artery (MCA) of 50 conscious cats. In the acute experiments, 10 cats were given mannitol (1.2 gm/kg intravenously) and 10 cats were untreated. The neurological status of the treated cats improved. Perfusion with a mixture of colloidal carbon and buffered paraformaldehyde was carried out from 30 minutes to 12 hours following MCA occlusion. Results of the morphological examination of the brains demonstrated that mannitol delayed the development of neuronal alterations and edema. Measurement of capillary luminal diameters in the ischemic cortex of the untreated cats revealed progressive narrowing with microcirculatory obstruction occurring at 6 hours. Capillary narrowing was absent or minimal in the treated cats during the initial 6 hours. Breakdown of the blood-brain barrier also was delayed by treatment. In the 30 subacute experiments, 10 cats were untreated, 10 cats received mannitol (1.2 gm/kg intravenously), and 10 cats were given a combination of mannitol and high-dose dexamethasone. Although early transient clinical improvement occurred in the treated animals, morphological findings in the brains of the treated and untreated cats following 48 hours of ischemia were not significantly different. Despite the finding that the beneficial effects of mannitol were relatively short-lived (6 to 12 hours), the delay in the development of irreversible changes probably is important as it would allow a longer period of time for the institution of a more definitive form of therapy.

Intracranial pressure, blood pressure, and pulse rate after occlusion of a middle cerebral artery in cats

The left middle cerebral artery was occluded in 12 tranquilized but unanesthetized cats with use of a device implanted transorbitally 5 to 7 days earlier. Bilateral epidural pressures, mean aortic blood pressure, and pulse rate were measured at intervals for up to 48 hours after occlusion. The relationships of these measurements to each other and to the extent and severity of cerebral infarcts is described.