Temporal profile of neuronal damage in a model of transient forebrain ischemia

This study examined the temporal profile of ischemic neuronal damage following transient bilateral forebrain ischemia in the rat model of four-vessel occlusion. Wistar rats were subjected to transient but severe forebrain ischemia by permanently occluding the vertebral arteries and 24 hours later temporarily occluding the common carotid arteries for 10, 20, or 30 minutes. Carotid artery blood flow was restored and the rats were killed by perfusion-fixation after 3, 6, 24, and 72 hours. Rats with postischemic convulsions were discarded. Ischemic neuronal damage was graded in accordance with conventional neuropathological criteria. Ten minutes of four-vessel occlusion produced scattered ischemic cell change in the cerebral hemispheres of most rats. The time to onset of visible neuronal damage varied among brain regions and in some regions progressively worsened with time. After 30 minutes of ischemia, small to medium-sized striatal neurons were damaged early while the initiation of visible damage to hippocampal neurons in the h1 zone was delayed for 3 to 6 hours. The number of damaged neurons in neocortex (layer 3, layers 5 and 6, or both) and hippocampus (h1, h3-5, paramedian zone) increased significantly (p less than 0.01) between 24 and 72 hours. The unique delay in onset of ischemic cell change and the protracted increase in its incidence between 24 and 72 hours could reflect either delayed appearance of ischemic change in previously killed neurons or a delayed insult that continued to jeopardize compromised but otherwise viable neurons during the postischemic period.

Small differences in intraischemic brain temperature critically determine the extent of ischemic neuronal injury

We have tested whether small intraischemic variations in brain temperature influence the outcome of transient ischemia. To measure brain temperature, a thermocouple probe was placed stereotaxically into the left dorsolateral striatum of rats prior to 20 min of four-vessel occlusion. Rectal temperature was maintained at 36-37 degrees C by a heating lamp, and striatal temperature prior to ischemia was 36 degrees C in all animals. Six animal subgroups were investigated, including rats whose intraischemic striatal brain temperature was not regulated, or was maintained at 33, 34, 36, or 39 degrees C. Postischemic brain temperature was regulated at 36 degrees C, except for one group in which brain temperature was lowered from 36 degrees C to 33 degrees C during the first hour of recirculation. Energy metabolites were measured at the end of the ischemic insult, and histopathological evaluation was carried out at 3 days after ischemia. Intraischemic variations in brain temperature had no significant influence on energy metabolite levels measured at the conclusion of ischemia: Severe depletion of brain ATP, phosphocreatine, glucose, and glycogen and elevation of lactate were observed to a similar degree in all experimental groups. The histopathological consequences of ischemia, however, were markedly influenced by variations in intraischemic brain temperature. In the hippocampus, CA1 neurons were consistently damaged at 36 degrees C, but not at 34 degrees C. Within the dorsolateral striatum, ischemic cell change was present in 100% of the hemispheres at 36 degrees C, but in only 50% at 34 degrees C. Ischemic neurons within the central zone of striatum were not observed in any rats at 34 degrees C, but in all rats at 36 degrees C. In rats whose striatal temperature was not controlled, brain temperature fell from 36 to 30-31 degrees C during the ischemic insult. In this group, no ischemic cell change was seen within striatal areas and was only inconsistently documented within the CA1 hippocampal region. These results demonstrate that (a) rectal temperature unreliably reflects brain temperature during ischemia; (b) despite severe depletion of brain energy metabolites during ischemia at all temperatures, small increments of intraischemic brain temperature markedly accentuate histopathological changes following 3-day survival; and (c) brain temperature must be controlled above 33 degrees C in order to ensure a consistent histopathological outcome. Lowering of the brain temperature by only a few degrees during ischemia confers a marked protective effect.

Pathologic correlates of incidental MRI white matter signal hyperintensities

We related the histopathologic changes associated with incidental white matter signal hyperintensities on MRIs from 11 elderly patients (age range, 52 to 82 years) to a descriptive classification for such abnormalities. Punctate, early confluent, and confluent white matter hyperintensities corresponded to increasing severity of ischemic tissue damage, ranging from mild perivascular alterations to large areas with variable loss of fibers, multiple small cavitations, and marked arteriolosclerosis. Microcystic infarcts and patchy rarefaction of myelin were also characteristic for irregular periventricular high signal intensity. Hyperintense periventricular caps and a smooth halo, however, were of nonischemic origin and constituted areas of demyelination associated with subependymal gliosis and discontinuity of the ependymal lining. Based on these findings, our classification appears to reflect both the different etiologies and severities of incidental MRI signal abnormalities, if it is modified to treat irregular periventricular and confluent deep white matter hyperintensities together.

Guidelines for Prevention of Stroke in Patients With Ischemic Stroke or Transient Ischemic Attack

The aim of this new statement is to provide comprehensive and timely evidence-based recommendations on the prevention of ischemic stroke among survivors of ischemic stroke or transient ischemic attack. Evidence-based recommendations are included for the control of risk factors, interventional approaches for atherosclerotic disease, antithrombotic treatments for cardioembolism, and the use of antiplatelet agents for noncardioembolic stroke. Further recommendations are provided for the prevention of recurrent stroke in a variety of other specific circumstances, including arterial dissections; patent foramen ovale; hyperhomocysteinemia; hypercoagulable states; sickle cell disease; cerebral venous sinus thrombosis; stroke among women, particularly with regard to pregnancy and the use of postmenopausal hormones; the use of anticoagulation after cerebral hemorrhage; and special approaches for the implementation of guidelines and their use in high-risk populations.

Viability thresholds and the penumbra of focal ischemia

The classic concept of the viability thresholds of ischemia differentiates between two critical flow rates, the threshold of electrical failure and the threshold of membrane failure. These thresholds mark the upper and lower flow limits of the ischemic penumbra which is thought to suffer only functional but not structural injury. Recent studies of the functional and metabolic disturbances suggest a more complex pattern of thresholds. At declining flow rates, protein synthesis is inhibited at first (at a threshold of about 0.55 ml/gm/min), followed by a stimulation of anaerobic glycolysis (at 0.35 ml/gm/min), the release of neurotransmitters and the beginning disturbance of energy metabolism (at about 0.20 ml/min), and finally the anoxic depolarization (< 0.15 ml/gm/min). The penumbra, as defined by the classic flow thresholds, does not remain viable for extended periods. Since viability of the tissue requires maintenance of energy-dependent metabolic processes, penumbra is redefined as a region of constrained blood supply in which the energy metabolism is preserved. Imaging of the penumbra by combining autoradiographic cerebral blood flow measurements with bioluminescent images of adenosine triphosphate (ATP) demonstrates a gradual expansion of the infarct core (in which ATP is depleted) into the penumbra until, after a few hours, the penumbra has disappeared. It is suggested that the limited survival of the penumbra is due to periinfarct depolarizations, which result in repeated episodes of tissue hypoxia, because the increased metabolic workload is not coupled to an adequate increase of collateral blood supply. This explains pharmacological suppression of periinfarct depolarizations lowering the threshold of metabolic disturbances and reducing the volume of the ischemic infarct.

Overexpression of BCL-2 in transgenic mice protects neurons from naturally occurring cell death and experimental ischemia

Naturally occurring cell death (NOCD) is a prominent feature of the developing nervous system. During this process, neurons express bcl-2, a major regulator of cell death whose expression may determine whether a neuron dies or survives. To gain insight into the possible role of bcl-2 during NOCD in vivo, we generated lines of transgenic mice in which neurons overexpress the human BCL-2 protein under the control of the neuron-specific enolase (NSE) or phosphoglycerate kinase (PGK) promoters. BCL-2 overexpression reduced neuronal loss during the NOCD period, which led to hypertrophy of the nervous system. For instance, the facial nucleus and the ganglion cell layer of the retina had, respectively, 40% and 50% more neurons than normal. Consistent with this finding, more axons than normal were found in the facial and optic nerves. We also tested whether neurons overexpressing BCL-2 were more resistant to permanent ischemia induced by middle cerebral artery occlusion; in transgenic mice, the volume of the brain infarction was reduced by 50% as compared with wild-type mice. These animals represent an invaluable tool for studying the effects of increased neuronal numbers on brain function as well as the mechanisms that control the survival of neurons during development and adulthood.

Clinical correlates of white matter findings on cranial magnetic resonance imaging of 3301 elderly people. The Cardiovascular Health Study

BACKGROUND AND PURPOSE

Our aim was to identify potential risk factors for and clinical manifestations of white matter findings on cranial MRI in elderly people.

METHODS

Medicare eligibility lists were used to obtain a representative sample of 5888 community-dwelling people aged 65 years or older. Correlates of white matter findings were sought among 3301 participants who underwent MRI scanning and denied a history of stroke or transient ischemic attack. Participants underwent extensive standardized evaluations at baseline and on follow-up, including standard questionnaires, physical examination, multiple blood tests, electrocardiogram, pulmonary function tests, carotid sonography, and M-mode echocardiography. Neuroradiologists graded white matter findings from 0 (none) to 9 (maximal) without clinical information.

RESULTS

Many potential risk factors were related to the white matter grade, but in the multivariate model the factors significantly (all P < .01) and independently associated with increased grade were greater age, clinically silent stroke on MRI, higher systolic blood pressure, lower forced expiratory volume in 1 second (FEV1), and income less than $50,000 per year. If excluded, FEV1 was replaced in the model by female sex, history of smoking, and history of physician-diagnosed hypertension at the baseline examination. Many clinical features were correlated with the white matter grade, especially those indicating impaired cognitive and lower extremity function.

CONCLUSIONS

White matter findings were significantly associated with age, silent stroke, hypertension, FEV1, and income. The white matter findings may not be considered benign because they are associated with impaired cognitive and lower extremity function.

The role of zinc in selective neuronal death after transient global cerebral ischemia

Zinc is present in presynaptic nerve terminals throughout the mammalian central nervous system and likely serves as an endogenous signaling substance. However, excessive exposure to extracellular zinc can damage central neurons. After transient forebrain ischemia in rats, chelatable zinc accumulated specifically in degenerating neurons in the hippocampal hilus and CA1, as well as in the cerebral cortex, thalamus, striatum, and amygdala. This accumulation preceded neurodegeneration, which could be prevented by the intraventricular injection of a zinc chelating agent. The toxic influx of zinc may be a key mechanism underlying selective neuronal death after transient global ischemic insults.

Tetracyclines inhibit microglial activation and are neuroprotective in global brain ischemia

Ischemic stroke is the most common life-threatening neurological disease and has limited therapeutic options. One component of ischemic neuronal death is inflammation. Here we show that doxycycline and minocycline, which are broad-spectrum antibiotics and have antiinflammatory effects independent of their antimicrobial activity, protect hippocampal neurons against global ischemia in gerbils. Minocycline increased the survival of CA1 pyramidal neurons from 10.5% to 77% when the treatment was started 12 h before ischemia and to 71% when the treatment was started 30 min after ischemia. The survival with corresponding pre- and posttreatment with doxycycline was 57% and 47%, respectively. Minocycline prevented completely the ischemia-induced activation of microglia and the appearance of NADPH-diaphorase reactive cells, but did not affect induction of glial acidic fibrillary protein, a marker of astrogliosis. Minocycline treatment for 4 days resulted in a 70% reduction in mRNA induction of interleukin-1beta-converting enzyme, a caspase that is induced in microglia after ischemia. Likewise, expression of inducible nitric oxide synthase mRNA was attenuated by 30% in minocycline-treated animals. Our results suggest that lipid-soluble tetracyclines, doxycycline and minocycline, inhibit inflammation and are neuroprotective against ischemic stroke, even when administered after the insult. Tetracycline derivatives may have a potential use also as antiischemic compounds in humans.

Lacunar strokes and infarcts: a review

At least 20 different lacunar syndromes have been described and can be recognized by characteristic clinical features. Almost all occur in patients with hypertension. Small lacunes are usually due to lipohyalinosis, larger ones to atheromatous or embolic occlusion of a penetrating vessel. The concept of the "lacunar state" is examined in the light of recent knowledge with the conclusion that the clinical deficit is primarily related to unrecognized normal pressure hydrocephalus rather than to the presence of a few lacunes. The notion that lacunes occur haphazardly is criticized because the first or only lacune tends to be symptomatic. The incidence of cerebral lacunes has declined since the introduction of antihypertensive therapy, an indication that therapy is effective.

Poly(ADP-ribose) polymerase gene disruption renders mice resistant to cerebral ischemia

Nitric oxide (NO) and peroxynitrite, formed from NO and superoxide anion, have been implicated as mediators of neuronal damage following focal ischemia, but their molecular targets have not been defined. One candidate pathway is DNA damage leading to activation of the nuclear enzyme, poly(ADP-ribose) polymerase (PARP), which catalyzes attachment of ADP ribose units from NAD to nuclear proteins following DNA damage. Excessive activation of PARP can deplete NAD and ATP, which is consumed in regeneration of NAD, leading to cell death by energy depletion. We show that genetic disruption of PARP provides profound protection against glutamate-NO-mediated ischemic insults in vitro and major decreases in infarct volume after reversible middle cerebral artery occlusion. These results provide compelling evidence for a primary involvement of PARP activation in neuronal damage following focal ischemia and suggest that therapies designed towards inhibiting PARP may provide benefit in the treatment of cerebrovascular disease.

Stroke protection by 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors mediated by endothelial nitric oxide synthase

The treatment of ischemic strokes is limited to prophylactic agents that block the coagulation cascade. Here, we show that cholesterol-lowering agents, 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors, protect against cerebral injury by a previously unidentified mechanism involving the selective up-regulation of endothelial NO synthase (eNOS). Prophylactic treatment with HMG-CoA reductase inhibitors augments cerebral blood flow, reduces cerebral infarct size, and improves neurological function in normocholesterolemic mice. The up-regulation of eNOS by HMG-CoA reductase inhibitors is not associated with changes in serum cholesterol levels, but is reversed by cotreatment with L-mevalonate and by the downstream isoprenoid, geranylgeranyl pyrophosphate and not by farnesyl pyrophosphate. The blood flow and neuroprotective effects of HMG-CoA reductase inhibitors are completely absent in eNOS-deficient mice, indicating that enhanced eNOS activity by HMG-CoA reductase inhibitors is the predominant if not the only mechanism by which these agents protect against cerebral injury. Our results suggest that HMG-CoA reductase inhibitors provide a prophylactic treatment strategy for increasing blood flow and reducing brain injury during cerebral ischemia.

In vivo evidence that erythropoietin protects neurons from ischemic damage

Erythropoietin (EPO) produced by the kidney and the liver (in fetuses) stimulates erythropoiesis. In the central nervous system, neurons express EPO receptor (EPOR) and astrocytes produce EPO. EPO has been shown to protect primary cultured neurons from N-methyl-D-aspartate (NMDA) receptor-mediated glutamate toxicity. Here we report in vivo evidence that EPO protects neurons against ischemia-induced cell death. Infusion of EPO into the lateral ventricles of gerbils prevented ischemia-induced learning disability and rescued hippocampal CA1 neurons from lethal ischemic damage. The neuroprotective action of exogenous EPO was also confirmed by counting synapses in the hippocampal CA1 region. Infusion of soluble EPOR (an extracellular domain capable of binding with the ligand) into animals given a mild ischemic treatment that did not produce neuronal damage, caused neuronal degeneration and impaired learning ability, whereas infusion of the heat-denatured soluble EPOR was not detrimental, demonstrating that the endogenous brain EPO is crucial for neuronal survival. The presence of EPO in neuron cultures did not repress a NMDA receptor-mediated increase in intracellular Ca2+, but rescued the neurons from NO-induced death. Taken together EPO may exert its neuroprotective effect by reducing the NO-mediated formation of free radicals or antagonizing their toxicity.

Moderate hyperglycemia augments ischemic brain damage: a neuropathologic study in the rat

We compared the effects of glucose injection with those of saline or mannitol on ischemic brain damage and brain water content in a four-vessel occlusion (4-VO) rat model, which simultaneously causes severe forebrain ischemia and moderate hindbrain ischemia. Glucose given before onset of ischemia was followed by severe brain injury, with necrosis of the majority of neocortical neurons and glia, substantial neuronal damage throughout the remainder of forebrain, and severe brain edema. By comparison, saline injection before forebrain ischemia resulted in only scattered ischemic damage confined to neurons and no change in the brain water content. Mannitol injection before 4-VO or D-glucose injection during or after 4-VO produced no greater forebrain damage than did the saline injection. Morphologic damage in the cerebellum, however, was increased by D-glucose injection given either before or during 4-VO. The results demonstrate that hyperglycemia before severe brain ischemia or during moderate ischemia markedly augments morphologic brain damage.

Gender-linked brain injury in experimental stroke

BACKGROUND AND PURPOSE

Premenopausal women are at lower risk than men for stroke, but the comparative vulnerability to tissue injury once a cerebrovascular incident occurs is unknown. We hypothesized that female rats sustain less brain damage than males during experimental focal ischemia and that the gender difference in ischemic outcome can be eliminated by ovariectomy.

METHODS

Age-matched male (M), intact female (F), and ovariectomized female (O; plasma estradiol: 4.1+/-1.6 pg/mL compared with 7.4+/-1.5 in F and 4.0+/-1.1 in M) rats from two different strains, normotensive Wistar and stroke-prone spontaneously hypertensive rats, were subjected to 2 hours of intraluminal middle cerebral artery occlusion, followed by 22 hours of reperfusion. Cerebral blood flow (CBF) was monitored throughout the ischemic period by laser-Doppler flowmetry. Infarction volume in the cerebral cortex (Ctx) and caudoputamen (CP) was determined by 2,3,5-triphenyltetrazolium chloride staining. In a separate cohort of M, F, and O Wistar rats, absolute rates of regional CBF were measured at the end of the ischemic period by quantitative autoradiography using [14C]iodoantipyrine.

RESULTS

F rats of either strain had a smaller infarct size in Ctx and CP and a higher laser-Doppler flow during ischemia compared with respective M and O rats. Mean end-ischemic CBF was higher in F compared with M and O rats in CP, but not in Ctx. Cerebrocortical tissue volume with end-ischemic CBF < 10 mL/100 g/min was smaller in F than M rats, but not different from O rats.

CONCLUSIONS

We conclude that endogenous estrogen improves stroke outcome during vascular occlusion by exerting both neuroprotective and flow-preserving effects.

Experimental cerebral ischemia in mongolian gerbils. I. Light microscopic observations

Light microscopic observations were carried out on Mongolian gerbils (Meriones unguiculatus) subjected to a partial cerebral ischemia by occlusion of the left common carotid artery at the neck. About 30% of gerbils developed an ischemic injury in the ipsilateral hemisphere and their brains revealed the following histopathologic features: 1. the changes were related to the intensity (duration) of the ischemic insult and to the time elapsed following release of the occlusion. The ischemic lesions appear to progress after re-establishment of the circulation and this presents one facet of a "maturation" phenomenon which seems to be a general principle applicable to various parameters of ischemic injury. The rate of "maturation" of the lesions is related to the intensity of the ischemic insult, a lesser intensity resulting in longer development of lesions. 2. The changes were either focal or diffuse in character. The former were assumed to be directly related to a vascular involvement; among the latter the topistic distribution of the hippocampal changes suggested a feature of selective vulnerability. 3. An indirect indication of neuronal recovery was surmised from observations on animals sacrificed after different periods following occlusions of the same duration. Also capable of recovery was a "reactive change" observed in the H3 neurons of the hippocampus. This change was characterized by central chromatolysis and resembled the "rimäre Reizung" of Nissl.

Ischemia-induced neuronal apoptosis

Hypoxic-ischemic neuronal death has long been considered to represent necrosis, but it now appears that many brain neurons undergo apoptosis after either global or focal ischemic insults. This event is probably substantially distinct from ischemia-triggered excitotoxicity, which tends to produce necrosis. While many questions remain unanswered, the concept of ischemic apoptosis has raised exciting prospects of combining anti-apoptotic with anti-excitotoxic treatments to achieve heightened therapeutic benefits in the brains of patients traumatized by cardiac arrest or stroke.

Enhanced expression of Iba1, ionized calcium-binding adapter molecule 1, after transient focal cerebral ischemia in rat brain

BACKGROUND AND PURPOSE

Iba1 is a novel calcium-binding protein and is specifically expressed in microglia in the brain. It has been suggested that Iba1 plays an important role in regulation of the function of microglia. In the present study we examined time-dependent Iba1 expression after transient middle cerebral artery occlusion and characterized microglial activation in various brain regions.

METHODS

Rat middle cerebral artery occlusion was induced by the intraluminal filament technique. After 1.5 hours of transient ischemia, Iba1 expression was examined by immunohistochemical and immunoblot analyses. The microglial activation in association with ischemic severity was characterized by double immunostaining with other specific markers.

RESULTS

In the peri-ischemic area, heavily Iba1 immunoreactive cells rapidly appeared at 3.5 hours after reperfusion. Immunoreactivity was further increased and peaked at 7 days. In the ischemic core, round Iba1-positive cells, which may be blood-borne monocytes, appeared from 24 hours and reached a peak at 4 to 7 days. Double immunostaining revealed that activated microglia in the peri-ischemic area upregulated Iba1 expression but were negative for the macrophage marker ED1. ED1-positive cells were clearly restricted to the ischemic core.

CONCLUSIONS

These findings suggest the following: (1) Iba1 expression may be associated with microglial activation in ischemic brain, and Iba1 immunostaining can be useful to evaluate the pathophysiological roles of activated microglia in ischemic injury. (2) Expression of ED1 antigen is strictly restricted to severe ischemic damage, whereas activated microglia in the peri-ischemic area showed Iba1 upregulation without ED1. Therefore, microglia may exhibit difference of antigenicity in the severity of ischemic brain injury.

The glutamate antagonist MK-801 reduces focal ischemic brain damage in the rat

Excessive activation of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor has been implicated in the sequence of neurochemical events that results in irreversible neuronal damage in cerebral ischemia. The effects of the NMDA antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate (MK-801) upon the amount of ischemic brain damage has been assessed quantitatively in the lightly anesthetized rat. Focal cerebral ischemia was produced by the permanent occlusion of one middle cerebral artery (MCA), and the animals were killed 3 hours after the arterial occlusion. MK-801 (0.5 mg/kg) was administered intravenously either 30 minutes prior to MCA occlusion or 30 minutes after the induction of ischemia. Pretreatment with MK-801 reduced the volume of ischemic damage both in the cerebral cortex (by 38% compared with untreated rats with MCA occlusion; p less than 0.01) and in the caudate nucleus (by 18% compared with controls; p less than 0.05). Treatment with MK-801, initiated 30 minutes after MCA occlusion, reduced the volume of ischemic damage in the cerebral cortex (by 52% compared with controls; p less than 0.01). The volume of ischemic damage in the caudate nucleus was minimally influenced by MK-801 treatment initiated after MCA occlusion. The antiischemic effects of MK-801 were readily demonstrable despite the hypotension that MK-801 induced in rats anesthetized with halothane (0.5%), nitrous oxide (70%), and oxygen (30%). The potency of MK-801 in reducing ischemic brain damage, even when administered after the induction of ischemia, highlights the potential use of NMDA receptor antagonists for the treatment of focal cerebral ischemia in humans.

Selective vulnerability in the gerbil hippocampus following transient ischemia

Following brief ischemia, the Mongolian gerbil is reported to develop unusual hippocampal cell injury (Brain Res 239:57--69, 1982). To further clarify this hippocampal vulnerability, gerbils were subjected to ischemia for 3, 5, 10, 20, and 30 min by bilateral occlusion of the common carotid arteries. They were perfusion-fixed after varying intervals of survival time ranging from 3 h up to 7 days. Following brief ischemia (5--10 min), about 90% of the animals developed typical hippocampal damage. The lesion was present throughout the extent of the dorsal hippocampus, whereas damage outside the hippocampus was not observed. Each sector of the hippocampus showed different types of cell reaction to ischemia. Ischemia cell change was seen in scattered CA4 neurons , and reactive change was found in CA2, whereas CA1 pyramidal cells developed a strikingly slow cell death process. Ischemia for 3 min did not produce hippocampal lesion in most cases. Following prolonged ischemia (20--30 min), brain injury had a wide variety in its extent and distribution. These results revealed that the gerbil brief ischemia model can serve as an excellent, reliable model to study the long-known hippocampal selective vulnerability to ischemia. Delayed neuronal death in CA1 pyramidal cells was confirmed after varying degrees of ischemic insult. These findings demonstrated that the pathology of neuronal injury following brief ischemia was by no means uniform nor simple.

Essential role of adenosine, adenosine A1 receptors, and ATP-sensitive K+ channels in cerebral ischemic preconditioning

Preconditioning with sublethal ischemia protects against neuronal damage after subsequent lethal ischemic insults in hippocampal neurons. A pharmacological approach using agonists and antagonists at the adenosine A1 receptor as well as openers and blockers of ATP-sensitive K+ channels has been combined with an analysis of neuronal death and gene expression of subunits of glutamate and gamma-aminobutyric acid receptors, HSP70, c-fos, c-jun, and growth factors. It indicates that the mechanism of ischemic tolerance involves a cascade of events including liberation of adenosine, stimulation of adenosine A1 receptors, and, via these receptors, opening of sulfonylurea-sensitive ATP-sensitive K+ channels.

A model of focal ischemic stroke in the rat: reproducible extensive cortical infarction

In the search for a more reproducible focal ischemic stroke model in the rat, we systematically interrupted blood flow to the right middle cerebral artery territory by ligating the right middle cerebral artery, and the right and left common carotid arteries in succession. Using a laser-Doppler flowmeter, we found that the relative surface blood flow in cerebral cortex supplied by the right middle cerebral artery decreased to 62, 48, and 18% of baseline respectively after successive ligation of the right middle cerebral artery, and the right and left common carotid arteries. A focal infarct in the cerebral cortex supplied by the right middle cerebral artery was consistently noted after ligation of the right middle cerebral and the right common carotid arteries and temporary clip occlusion of the left common carotid artery for 60 min. The surface areas of infarction measured 100 +/- 6 mm2 and the maximal cross-sectional area of infarction was 10.4 +/- 1.1 mm2 (N = 10). The mortality rate was 7% (N = 70). The characteristic changes of ischemic necrosis were limited to the cortex with sparing of subcortical structures. No motor deficits occurred. Occlusion of the right middle cerebral artery alone or together with the right common carotid artery did not consistently cause gross infarction and the maximal cross-sectional area of infarction was smaller (the right middle cerebral artery, 1.7 +/- 0.8 mm2, N = 10; the right middle cerebral artery plus the right common carotid artery, 4.8 +/- 1.9 mm2, N = 10). Permanent ligation of the right middle cerebral artery and both common carotid arteries had a high mortality (60% in 3 days, N = 10).(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral protection in homozygous null ICAM-1 mice after middle cerebral artery occlusion. Role of neutrophil adhesion in the pathogenesis of stroke

Acute neutrophil (PMN) recruitment to postischemic cardiac or pulmonary tissue has deleterious effects in the early reperfusion period, but the mechanisms and effects of neutrophil influx in the pathogenesis of evolving stroke remain controversial. To investigate whether PMNs contribute to adverse neurologic sequelae and mortality after stroke, and to study the potential role of the leukocyte adhesion molecule intercellular adhesion molecule-1 (ICAM-1) in the pathogenesis of stroke, we used a murine model of transient focal cerebral ischemia consisting of intraluminal middle cerebral artery occlusion for 45 min followed by 22 h of reperfusion. PMN accumulation, monitored by deposition of 111In-labeled PMNs in postischemic cerebral tissue, was increased 2.5-fold in the ipsilateral (infarcted) hemisphere compared with the contralateral (noninfarcted) hemisphere (P < 0.01). Mice immunodepleted of neutrophils before surgery demonstrated a 3.0-fold reduction in infarct volumes (P < 0.001), based on triphenyltetrazolium chloride staining of serial cerebral sections, improved ipsilateral cortical cerebral blood flow (measured by laser Doppler), and reduced neurological deficit compared with controls. In wild-type mice subjected to 45 min of ischemia followed by 22 h of reperfusion, ICAM-1 mRNA was increased in the ipsilateral hemisphere, with immunohistochemistry localizing increased ICAM-1 expression on cerebral microvascular endothelium. The role of ICAM-1 expression in stroke was investigated in homozygous null ICAM-1 mice (ICAM-1 -/-) in comparison with wild-type controls (ICAM-1 +/+). ICAM-1 -/- mice demonstrated a 3.7-fold reduction in infarct volume (P < 0.005), a 35% increase in survival (P < 0.05), and reduced neurologic deficit compared with ICAM-1 +/+ controls. Cerebral blood flow to the infarcted hemisphere was 3.1-fold greater in ICAM-1 -/- mice compared with ICAM-1 +/+ controls (P < 0.01), suggesting an important role for ICAM-1 in the genesis of postischemic cerebral no-reflow. Because PMN-depleted and ICAM-1-deficient mice are relatively resistant to cerebral ischemia-reperfusion injury, these studies suggest an important role for ICAM-1-mediated PMN adhesion in the pathophysiology of evolving stroke.