NG-nitro-L-arginine methyl ester reduces necrotic but not apoptotic cell death induced by reversible focal ischemia in rat

During cerebral ischemia, nitric oxide (NO) production via stimulation of NO synthase, is likely one of the major events leading to neuronal death. Recently, we have demonstrated that after reversible focal ischemia, apoptosis was implicated in the penumbra whereas necrosis was prominent in the ischemic core. We have now examined the effect of a non-specific inhibitor of NO synthase, NG-nitro-L-arginine methyl ester (L-NAME, 3 ing kg-1 i.p., 5 min and 3 h after the onset of ischemia), on the progress of apoptotic and necrotic nuclei following transient focal cerebral ischemia, using DNA electrophoresis and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick-end labeling (TUNEL assay). Our results indicated that L-NAME prevented the loss of necrotic, but not apoptotic cells.     

Axonal injury caused by focal cerebral ischemia in the rat

The susceptibility of axons to blunt head injury is well established. However, axonal injury following cerebral ischemia has attracted less attention than damage in gray matter. We have employed immunocytochemical methods to assess the vulnerability of axons to cerebral ischemia in vivo. Immunocytochemistry was performed using antibodies to a synaptosomal-associated protein of 25 kDa (SNAP25), which is transported by fast anterograde transport; the 68-kDa neurofilament subunit (NF68kD); and microtubule-associated protein 5 (MAP5) on sections from rats subjected to 30 min and 1, 2, and 4 h of ischemia induced by permanent middle cerebral artery (MCA) occlusion. After 4 h of occlusion, there was increased SNAP25 immunoreactivity, which was bulbous in appearance, reminiscent of the axonal swellings that occur following blunt head injury. Increased SNAP25 immunoreactivity was present in circumscribed zones in the subcortical white matter and in the axonal tracts at the border of infarction, a pattern similar to that previously described for amyloid precursor protein. Although less marked, similar changes in immunoreactivity in axons were evident following 2 h of ischemia. MAP5 and NF68kD had striking changes in immunoreactivity in axonal tracts permeating the caudate nucleus within the MCA territory at 4 h. The appearance was roughened and disorganized compared with the smooth regular staining in axons within the nonischemic areas. Profiles reminiscent of axonal bulbs were evident in MAP5-stained sections. The changes seen with NF68kD and MAP5 were also evident at 2 h but were more subtle at 1 h. There were no changes in axonal immunoreactivity with SNAP25 or NF68kD at 30 min after MCA occlusion. Altered immunoreactivity following ischemia using SNAP25, MAP5, and NF68kD provides further evidence for the progressive breakdown of the axonal cytoskeleton following an ischemic insult. NF68kD and MAP5 appear to be sensitive markers of the structural disruption of the cytoskeleton, which precedes the subsequent accumulation of SNAP25 within the damaged axons. Axonal cytoskeletal breakdown and disruption of fast axonal transport, which are well-recognized features of traumatic brain injury, are also sequalae of an ischemic insult.     

Effects of postischemic halothane administration on outcome from transient focal cerebral ischemia in the rat

BACKGROUND: Serologic methods to detect Helicobacter pylori in infants, especially in developing countries, may be limited because of decreased immune response caused by malnutrition. The true prevalence may therefore be underestimated in this age group. Urea breath test is considered to be a good screening method in children but is expensive and therefore is not suitable for screening in developing countries. Simple, inexpensive, and accurate noninvasive methods to detect H. pylori in infants and young children are needed. METHODS: Enzyme immunoassay (EIA) and immunoblot (IB) serologic analyses, 13C-urea breath test (UBT), and immunomagnetic separation--polymerase chain reaction (IMS-PCR) were performed on stool specimens, to detect H. pylori in 68 children between 4 and 24 months of age (mean, 11.5 months) in an endemic area in Bangladesh and the results compared. RESULTS: The occurrence of H. pylori was 57% (n=39) using only UBT, 60% (n=41) using only IMS-PCR, and 78% (n=53) using UBT and IMS-PCR together. The concordance between UBT and IMS-PCR results was 62%. Immunoblot was positive in only 9% (n=6). Results in all 68 children were negative using EIA. DISCUSSION: The prevalence of H. pylori infection in this periurban community and age group was high. Only serologic methods seem to be unsatisfactory for screening of H. pylori infection in infants and may not reflect the true prevalence. Immunomagnetic separation-PCR is a simple and rapid method for detection of H. pylori in stool and is an attractive method for analysis of colonization in infants. However, it may reflect a different stage of disease than UBT. Further studies are needed to clarify this.     

Apoptosis and programmed cell death: a role in cerebral ischemia

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. Recent studies demonstrated: 1) DNA cleavage into oligonucleosome-sized fragments demonstrated by a typical ladder pattern; 2) early endonuclease activation, as demonstrated by the presence of high molecular weight DNA fragments (300 to 50 kbp); 3) chromatin condensation and apoptotic bodies formation; 4) activation of apoptosis-associated proteins. These results may indicate that apoptosis contributes to the development of the ischemic infarct and is probably substantially distinct from ischemia-triggered excitotoxicity, which tends to produce necrosis.     

Calcitonin gene-related peptide reduces brain injury in a rat model of focal cerebral ischemia

BACKGROUND AND PURPOSE: Calcitonin gene-related peptide is an endogenous vasodilating neuropeptide with a dense concentration in the trigeminocerebrovascular system. It is hypothesized that depletion of this peptide contributes to delayed cerebral ischemia after subarachnoid hemorrhage and that an exogenous supply of calcitonin gene-related peptide will augment ischemic cerebral blood flow and reduce neuronal injury. METHODS: In this study we have investigated the effect of an intravenous infusion of calcitonin gene-related peptide (100 ng/kg per minute), started 1 hour before and continued throughout 4 hours of focal cerebral ischemia, on cerebral blood flow and the volume of brain injury in a rat model of middle cerebral artery occlusion. RESULTS: Calcitonin gene-related peptide produces a significant improvement in ischemic cerebral blood flow (32 +/- 2 compared with 13 +/- 2 mL/100 g per minute in the controls; t = 6.92, P < .0001) with a concomitant reduction in the volume of ischemic brain injury (102 +/- 22 compared with 234 +/- 19 mm3; t = 4.47, P < .001). CONCLUSIONS: These findings lend support for the potential use of this peptide in the prophylactic treatment of delayed cerebral ischemia after aneurysmal subarachnoid hemorrhage.     

An integrated analysis of the progression of cell responses induced by permanent focal middle cerebral artery occlusion in the rat

Defining the chronology and severity of cell damage in an evolving lesion after ischemia is important for understanding the underlying mechanisms in the development of therapeutic intervention. In the present study, we used a combination of histological and immunocytochemical methods to evaluate cell responses from 30 min to 48 h after permanent occlusion of the middle cerebral artery (MCAO) in the rat. Specific immunocytochemical markers clearly revealed acute early responses in neurons (neurofilament protein 200), astrocytes (glial fibrillary acidic protein), and microglia/macrophages (OX-42 and ED-1) such as enlarged, convoluted neuronal processes, and disintegration of glia. Progressive topographic changes in the developing lesion, pinpointed by immunolabeling, indicated the severity and extension of the cell damage. Proliferation and hypertrophy of astrocytes and microglia around the infarct, and contralaterally, occurred 24-48 h after MCAO and coincided with mass necrosis and infiltration of neutrophils and macrophages into the core. These observations corroborate the suggestion that the inflammatory process is involved in the progression of the infarct.     

Enhanced vulnerability to apoptotic cell death in sporadic Alzheimer's disease

All important neuropathological features like neurodegeneration and amyloid deposition occur similarly in familial and in sporadic Alzheimer's disease (AD) patients, suggesting a common pathogenetic mechanism. We investigated whether defective vulnerabilty to the induction of the apoptotic cell death pathway might be one of the underlying mechanisms leading to progressive cell death in sporadic AD. Our test could prove useful in supporting the diagnosis of AD and in predicting individuals predisposed to AD.     

SPARC/osteonectin mRNA is induced in blood vessels following injury to the adult rat cerebral cortex

Recently we described the pattern of expression of the anti-adhesive glycoprotein SPARC/osteonectin in the developing and adult brain. SPARC mRNA was present in developing blood vessels during neurogenesis, but was not detected in the mature vasculature. We have now examined the effect of a lesion to the adult rat cerebral cortex on the expression of SPARC by in situ hybridization. SPARC mRNA was increased in the zone proximal to the wound at 3 to 10 days after cortical brain injury. During this period, SPARC was induced in mature blood vessels close to the lesion site and in blood vessels which develop following injury. These results suggest a role for SPARC in the process of angiogenesis following injury to the adult cerebral cortex.     

Maturation-dependent apoptotic cell death of oligodendrocytes in myelin-deficient rats

Early geographic relocation has been implicated as an important correlate of psychopathology, learning difficulties, and behavioural problems among child and adolescent populations, yet systematic studies of the potential influence of relocation on youthful drug use have not been conducted. This study explored the relationship between number of geographic moves before the age of 16 and the timing of onset of drug use and progression to drug-related problems. Data were obtained from 3,700 young adults aged 18 to 35 years participating in the 1990-1991 Ontario Mental Health Supplement, a large random probability survey of the residents of the Province of Ontario, Canada. Holding constant potential confounding factors, results showed highly significant positive relationships between moving and early initiation of illicit drugs including marijuana, hallucinogens, crack/cocaine, and illicit use of prescribed drugs. Among marijuana users, moving was also associated with a hastening of time to marijuana-related problems. Relationships between moving and measures of alcohol use/problems (onset of first drink, onset of any alcohol-related problem) were either weak or nonsignificant. Important sex differences were found, with statistically significant relationships between moving and early drug use initiation and progression occurring primarily among males. Future research is required to test for possible mediating mechanisms linking relocation with drug use as well as moderating influences. Efforts should also focus on finding out why drug use appears to be a more common response to relocation among boys.     

Ischemic damage and subsequent proliferation of oligodendrocytes in focal cerebral ischemia

In order to achieve a better understanding of the pathophysiology of ischemic white matter lesions, oligodendrocytic degeneration and subsequent proliferation were examined in the mouse model of middle cerebral artery occlusion. In situ hybridization histochemistry for proteolipid protein messenger RNA was employed as a sensitive and specific marker of oligodendrocytes, and immunohistochemistry for myelin basic protein was used as a compact myelin marker. Immunohistochemistry for microtubule-associated protein 2 and albumin was employed to monitor neuronal degeneration and the breakdown of the blood brain barrier, respectively. In the ischemic core of the caudoputamen, the immunoreactivity for microtubule-associated protein 2 disappeared and massive albumin extravasation occurred several hours after vessel occlusion, while proteolipid protein messenger RNA signals remained relatively strong at this time. The messenger RNA signals began to attenuate 12 h after ischemia and were hardly detectable 24 h after ischemia in the whole ischemic lesion. In situ end-labeling of fragmented DNA showed some cells with proteolipid protein messenger RNAs to have DNA fragmentation at this period. In contrast to proteolipid protein messenger RNA signals, the immunoreactivity for myelin basic protein was detected as long as five days after ischemia. An apparent increase in the cells possessing strong proteolipid protein messenger RNA signals was found five days after ischemia, mainly in the corpus callosum and the cortex bordering the infarcted areas. A double simultaneous procedure with in situ hybridization for proteolipid protein messenger RNA and immunohistochemistry for glial fibrillary acid protein or lectin histochemistry for macrophages/microglia showed proliferating oligodendrocytes to be co-localized with reactive astrocytes and macrophages/microglia. These findings show that oligodendrocytic damage occurred following ischemic neuronal damage and the breakdown of the blood brain barrier, but preceded the breakdown of myelin proteins in the ischemic lesion, that an apoptosis-like process was involved in ischemic oligodendrocytic death, and that surviving oligodendrocytes responded and proliferated in the outer border of the infarcted area.     

Orchidectomy induces a wave of apoptotic cell death in the epididymis

The epididymis is the site where spermatozoa are matured and stored. After orchidectomy, this tissue loses up to 80% of its weight. In the prostate, androgen withdrawal by orchidectomy is associated with apoptotic cell death. The objective of the present study was to investigate whether apoptotic cell death is involved in the androgen-dependent weight loss found in the rat epididymis after orchidectomy. Adult male Sprague-Dawley rats were orchidectomized, and apoptotic cells were identified by in situ TUNEL (TdT-mediated dUTP-digoxigenin nick end-labeling) apoptosis detection. Apoptosis first appeared in the epithelium of the initial segment of the epididymis 18 h after orchidectomy, reached a maximum on day 2, and disappeared by day 5 postorchidectomy. In the caput epididymidis, apoptosis was first found after 24 h, reached a maximum by day 3, and was detectable until day 5. In the corpus epididymidis, apoptosis was first seen on day 4, peaked on day 5, and was undetectable by day 6 postorchidectomy. In the cauda epididymidis, apoptosis was first seen on day 5, peaked on day 6, and was occasionally detected on day 7. Throughout the rat epididymis, apoptotic cell death was localized specifically to principal cells. The presence of apoptosis was confirmed with the observation of a ladder of nucleosomal sized DNA fragmentation by using agarose gel electrophoresis. Androgen replacement therapy after orchidectomy demonstrated that apoptosis in the caput, corpus, and cauda epididymidis was androgen dependent. However, androgens alone could not completely prevent apoptosis in the initial segment of the epididymis. Efferent duct ligation induced a similar pattern of apoptosis in the initial segment of the epididymis as that seen after orchidectomy, but there were fewer apoptotic cells in the caput epididymidis, and no apoptotic cell death in the corpus and cauda epididymidis. We conclude that withdrawal of androgen by orchidectomy induces a wave of apoptotic cell death in the epididymis; we hypothesize that apoptosis in the initial segment is caused primarily by withdrawal of androgen as well as by luminal components coming from the testis.     

Identification of collaterally perfused areas following focal cerebral ischemia in the rat by comparison of gradient echo and diffusion-weighted MRI

Diffusion-weighted (DW) and gradient echo (GE) magnetic resonance images were acquired before and after occlusion of the middle cerebral artery (MCA) in the rat. Upon occlusion, an increase in DW imaging signal intensity was observed in a core area within the MCA territory, most likely reflecting cytotoxic edema. The signal from GE images, which is sensitive to changes in the absolute amount of deoxyhemoglobin, decreased following ischemia within a region that extended beyond the core area observed with DW imaging. This hypointensity is attributed to increases in blood volume and/or oxygen extraction fraction, which result from a decrease in perfusion pressure in the collaterally perfused area. The evolution of the GE imaging signal intensity from different regions was studied for 3.5 h following the occlusion. In the core area, the GE imaging signal returned towards baseline values after approximately 1-2 h, while it remained stable in the surrounding area. This feature may reflect a decrease in hematocrit due to microcirculatory defect and/or a decrease in the oxygen extraction fraction due to ongoing infarction of the tissue and may indicate that tissue recovery is severely compromised. The combined use of DW and GE imaging offers great promise for the noninvasive identification of specific pathological events with high spatial resolution.     

Late-onset lipid peroxidation and neuronal cell death following transient forebrain ischemia in rat brain

The receptor encoded by the W (c-kit) locus is expressed on the membrane of mouse primordial germ cells, whereas its ligand termed stem cell factor (SCF), encoded by the Sl locus, is expressed on the membrane of somatic cells associated with both the primordial germ cell migratory pathways and homing sites. Using an in vitro short time assay which allows a quantitative measure of adhesion between cells, in the present paper we show that SCF/c-kit interaction can modulate primordial germ cell adhesion to somatic cells. We report that the adhesiveness of 11.5 dpc primordial germ cells to four types of somatic cells in culture (TM4 cells, STO fibroblasts, bone marrow stromal cells and gonadal somatic cells) is significantly reduced by antibodies directed against c-kit receptor or SCF, as well by soluble SCF. This SCF/c-kit mediated adhesion seems independent of SCF-induced tyrosine autophosphorylation of c-kit receptor. Moreover, primordial germ cells showed a poor ability to adhere to a bone marrow stromal cell line carrying the Sl(d) mutation (unable to synthesize membrane-bound SCF). This adhesiveness was not further impaired by anti-c-kit antibody. These results demonstrate that SCF/c-kit interaction contributes to the adhesion of primordial germ cells to somatic cells in culture and suggest that the role played by SCF in promoting survival, proliferation and migration of these cells in vitro and in vivo, demonstrated by several studies, might depend on the ability of the membrane-bound form of this cytokine to directly mediate primordial germ cell adhesion to the surrounding somatic cells.     

Intraluminal increase of superoxide anion following transient focal cerebral ischemia in rats

OBJECTIVES: We studied the triggering mechanism for neurally mediated syncope. BACKGROUND: Although increased transient sympathetic tone is thought to be necessary for the development of neurally mediated syncope, little is known about the triggering mechanism for neurally mediated syncope. METHODS: Plasma epinephrine (EP) and norepinephrine (NE) levels were assessed in 20 syncope patients during tilt test (80 degrees, 15 min) with and without isoproterenol (ISP, 0.01, 0.02 microg/kg/min). If syncope occurred, propranolol (0.1 mg/kg) was injected. RESULTS: Eight patients experienced syncope during tilting alone, and 9 patients required ISP for syncope. In the negative response without ISP, NE showed a small statistical 1.7-fold increase at end of tilting and EP did not change during tilting. When syncope occurred during tilting alone, a significant 11.7-fold increase in EP at syncope was registered concomitant with a small 2.5-fold increase in NE. When patients experienced syncope during tilting with ISP, a significant 5.0-fold increase in EP at syncope was registered concomitant with a small 1.7-fold increase in NE. In patients without ISP, propranolol did not interrupt syncope. In patients with ISP, six of eight receiving propranolol responded to tilting negatively. CONCLUSIONS: An increase of NE levels may result in inhibition of syncope and an EP surge may be a triggering mechanism for neurally mediated syncope. Comparatively low levels of EP may be enough to induce syncope during tilting with ISP compared with tilting alone. Propranolol is not effective in patients without ISP, but it frequently inhibits syncope in patients with ISP. Propranolol (0.1 mg/kg) may be insufficient to block the actions of high levels of circulating EP.     

Cytosolic redistribution of cytochrome c after transient focal cerebral ischemia in rats

Recent in vitro cell-free studies have shown that cytochrome c release from mitochondria is a critical step in the apoptotic process. The present study examined the expression of cytochrome c protein after transient focal cerebral ischemia in rats, in which apoptosis was assumed to contribute to the expansion of the ischemic lesion. In situ labeling of DNA breaks in frozen sections after 90 minutes of middle cerebral artery (MCA) occlusion showed a significant number of striatal and cortical neurons, which were maximized at 24 hours after ischemia, exhibiting chromatin condensation, nuclear segmentation, and apoptotic bodies. Cytosolic localization of cytochrome c was detected immunohistochemically in the ischemic area as early as 4 hours after 90 minutes of MCA occlusion. Western blot analysis of the cytosolic fraction revealed a strong single 15-kDa band, characteristic of cytochrome c, only in the samples from the ischemic hemisphere. Western blot analysis of the mitochondrial fraction showed a significant amount of mitochondrial cytochrome c in nonischemic brain, which was decreased in ischemic brain 24 hours after ischemia. These results provide the first evidence that cytochrome c is being released from mitochondria to the cytosol after transient focal ischemia. Although further evaluation is necessary to elucidate its correlation with DNA fragmentation, our results suggest the possibility that cytochrome c release may play a role in DNA-damaged neuronal cell death after transient focal cerebral ischemia in rats.     

Involvement of platelet-activating factor in cell death induced under ischemia/postischemia-like conditions in an immortalized hippocampal cell line

The involvement of platelet-activating factor (PAF) in cell damage induced by ischemia/postischemia-like conditions was studied in a hippocampus-derived cell line, HN33.11. Cells exposed to N2-saturated glucose-free HEPES-buffered saline (ischemia) for 5 h followed by 18 h of incubation in serum-free control medium (postischemia reincubation) remained 67.4 +/- 2.4% viable in comparison with sham-treated cells. Analysis of DNA fragmentation in combination with Hoechst 33258 staining indicates that apoptosis is the dominant mode of cell death in the present model. PAF level during 10 h of ischemia was unchanged. However, an increase in PAF accumulation was found early during the reincubation period that followed 5 h of ischemia. Peak PAF concentrations were noted at 2 h after initiation of reincubation and rapidly declined to control level after 7 h of reincubation. Consistent with a role of PAF in mediating cell death under ischemia/postischemia reincubation in this model, the PAF antagonist BN 50739 exerted a dose-dependent protective effect. Maximal protection (85.7 +/- 5.4%) of the cells from ischemia/reincubation-induced cell damage was achieved at 0.1 microM BN 50739. The PAF antagonist lacked any protective effect against ischemia-induced cell death. On the other hand, the addition of the stable PAF analogue 1-O-hexadecyl-2-N-methylcarbamyl-sn-glycero-3-phosphocholine (MC-PAF) at the onset of ischemia potentiated ischemia/reincubation-induced apoptosis--an effect that was blocked by BN 50739. Pretreatment of HN33.11 cells with the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N,N-tetraacetic acid acetoxymethyl ester (BAPTA-AM) also provided a protective effect against ischemia/reincubation-induced cell damage. BAPTA-AM increased cell viability by 50%. Pretreatment with BAPTA-AM also decreased ischemia/reincubation-induced PAF accumulation in HN33.11 cells. The results suggest that PAF, acting via a PAF receptor, is at least in part mediating apoptosis under ischemia/postischemia-like conditions in HN33.11 cells.     

Diminution of preprosomatostatin-mRNA in cerebral cortex of the aged rat

The aim of the present study was to examine the effect of normal aging on somatostatin neurotransmission. Somatostatin gene expression was analysed in several regions of the cerebral cortex and hippocampus in 3, 7 and 21 month-old Sprague-Dawley rats using quantitative in situ hybridization with a 48mer oligodeoxynucleotide antisense probe. Furthermore the distribution of 125I-Tyr11 somatostatin receptor binding sites was studied using quantitative receptor autoradiography. The results demonstrated a significant reduction of preprosomatostatin-mRNA in the frontal cortex of the aged (21 month) group compared with the young (3 month) and the middle-aged (7 month) groups. The receptor binding densities of the aged (21 month) group tended to be lower, compared to the other groups although no significant region-specific changes were evident. These results indicate neurochemical changes in somatostatin-containing neurons in the frontal cortex during aging.     

Cerebral protection by intermittent reperfusion during temporary focal ischemia in the rat

Temporary arterial occlusion has been routinely used as an adjunct in intracranial aneurysm surgery. This has commonly been performed using a protocol of multiple short periods of occlusion alternating with periods of restoration of normal circulation. Recently, the logical basis of this method has come under scrutiny. There is extensive experimental evidence to suggest that repetitive, brief periods of global ischemia may cause more severe cerebral injury than an equivalent single period of global ischemia. Only recently has this issue begun to be addressed with regard to focal ischemia. Hence, despite the common use of temporary clipping, little experimental data are available regarding the ischemic consequences of temporary arterial occlusion with periods of reperfusion versus uninterrupted temporary occlusion. To investigate this issue, a protocol of occlusion/reperfusion that simulates the temporal profile that occurs during surgery was performed in a rat model of focal ischemia. Sixteen anesthetized Sprague-Dawley rats were divided into two groups. The animals in Group I underwent 60 minutes of uninterrupted middle cerebral artery occlusion and the animals in Group II were subjected to six separate 10-minute occlusion periods with 5 minutes of reperfusion between occlusions. Histopathological analysis was performed 72 hours postischemia. Group I had significantly increased mean infarction volumes (50.0 +/- 12.1 mm3) compared to Group II (8.7 +/- 3.1 mm3) (p = 0.008). Injuries in Group I occurred in both the cortex and striatum, whereas Group II showed only striatal injuries. Furthermore, the extent of the injuries in Group II was less severe, characterized by ischemic neuronal injury rather than frank infarction. The results indicate that intermittent reperfusion is neuroprotective during temporary focal ischemia and support the hypothesis that intermittent reperfusion is beneficial if temporary clipping is required during aneurysm repair.     

Induction of ischemic tolerance following brief focal ischemia in rat brain

The objective of this study was to determine whether brief focal ischemia induces ischemic tolerance in rat brain. Focal ischemia was produced in Wistar rats by occluding the middle cerebral artery (MCA) for 20 min at a distal site. Following recovery for 24 h, the animals were subjected to a 10-min episode of forebrain ischemia using a combination of bilateral carotid artery occlusion and systemic hypotension. Histologic injury, assessed after a survival period of 3-4 days, consisted of selective neuronal necrosis bilaterally in cerebral cortex, striatum, hippocampus, and thalamus superimposed upon a small cortical infarct adjacent to the site of MCA occlusion. However, the intensity of neuronal necrosis in the MCA territory of the neocortex ipsilateral to MCA occlusion was markedly less than that in the contralateral MCA cortex. In contrast, the extent of neuronal necrosis in subcortical structures was similar in both hemispheres. Unexpectedly, animals in which the MCA was manipulated, but not occluded, also exhibited a marked reduction of neuronal necrosis in the ipsilateral MCA neocortex following forebrain ischemia. However, in animals with craniotomy alone, forebrain ischemia caused a similar extent of neuronal necrosis in the MCA neocortex of both hemispheres. Transient occlusion of the MCA induced the focal expression of the 72-kDa heat-shock protein (hsp72) in the MCA territory of the neocortex. Limited expression of hsp72 was also detected following sham occlusion, but not after craniotomy alone. These results demonstrate focal induction of ischemic tolerance in rat neocortex that may be related to expression of heat-shock proteins.