Transient hyperthermia protects against subsequent forebrain ischemic cell damage in the rat

p53 expression in brain after middle cerebral artery occlusion in the rat

The purpose of this study is to determine whether the p53 protein, a product of the p53 tumor suppressor gene, that has been associated with the 72 kDa heat shock protein (hsp72), is expressed in ischemic brain. Adult Wistar rats (n = 5) were subjected to 120 minutes of middle cerebral artery occlusion. Twelve hours after reopening the artery, brain tissue was analyzed to determine the extent of neuronal damage (hematoxylin and eosin), and the distribution of p53 and hsp72 (monoclonal antibodies). Our data demonstrate that p53 is expressed in regions of neuronal necrosis; in contrast, morphologically intact neurons express hsp72. The data suggest that the presence of p53 is associated with cell death and that hsp72 may regulate p53 function.

Zinc toxicity and induction of the 72 kD heat shock protein in primary astrocyte culture

Zinc is a potent inducer of the 72 kD heat shock protein (HSP72). In brain, pathological conditions such as ischemia and seizures increase extracellular zinc. The present study examines the effect of zinc on HSP72 expression in rat primary cortical astrocyte culture. Astrocytes were grown to confluence and exposed to zinc chloride in CO2-equilibrated Earle's buffered salt solution. Expression of HSP72 was examined using immunocytochemistry. HSP72 was induced with zinc concentrations of 5 to 100 microM after 4 h exposures, or 200 to 300 microM after 15 min exposures. At the lower concentrations expression occurred in small clusters of contiguous cells. At concentrations high enough to cause cell death, HSP72-positive astrocytes formed a continuous margin around patches of dead cells. These patterns of HSP72 expression are similar to the patterns seen after cerebral ischemia in vivo. Exposure to zinc at 100 microM for 4 h or 400 microM for 15 min caused greater than 90% cell death. Increases in extracellular zinc may contribute to HSP72 induction and astrocyte death under ischemia and other pathological conditions in brain.

MK-801 and ketamine induce heat shock protein HSP72 in injured neurons in posterior cingulate and retrosplenial cortex

MK-801 and ketamine are noncompetitive N-methyl-D-aspartate (NMDA) receptor blockers that decrease brain injury in animal models of focal and global ischemia. Recent reports, however, suggested that MK-801 itself can damage neurons. Here we show that MK-801 (0.1 to 5.0 mg/kg) and ketamine (40 to 100 mg/kg) typically induce heat shock protein HSP72 mainly in layer 3 neurons of the posterior cingulate and retrosplenial cortex of the rat. These HSP72-immunoreactive neurons contain abnormal cytoplasmic vacuoles visualized by electron microscopy. The HSP72 immunoreactivity is maximal at 24 hours with 1.0-mg/kg doses of MK-801 and disappears by 2 weeks. Based on these data, we propose: (1) MK-801 and ketamine injure selected neurons, which express HSP72 in response to that injury. (2) Since HSP72 is induced for 1 to 2 weeks, the prolonged psychological side effects of MK-801, ketamine, phencyclidine, and related drugs could be related to this injury. (3) The neuroprotective effect of MK-801 is probably not related to HSP72 induction. (4) HSP72 immunocytochemistry is useful for studying nonlethal neuronal injury from a wide variety of brain insults.

Axon-glia exchange of macromolecules

The periaxonal and perineurial glia of crayfish and squid are strategically situated to regulate the neuronal microenvironment. Diverse molecules rapidly traverse the periaxonal sheath and a fraction of them enters the axons from glia or the glia from axons. The significance of these intercellular exchanges has not been tested directly. However, recent reports suggest that stress proteins, which probably are synthesized by both types of glia and transferred to axons, may be essential components by which the glia directly and indirectly assist neurons in tolerating ambient stress.

Heat shock protects cultured neurons from glutamate toxicity

Expression of heat shock proteins (HSPs) occurs in brain after ischemia and status epilepticus. We report that induction of the heat shock response in cortical cultures protects neurons from glutamate-induced excitotoxicity. Cultures heated to 42.2 degrees C for 20 min showed an overall decrease in protein synthesis but an increase in the synthesis of approximately 72 and approximately 85 kd proteins and in the levels of HSP70 mRNA. Heat shock inhibited excitotoxicity in cells exposed to glutamate at 3 or 24 hr following heat exposure, but not when the interval between heat and glutamate exposure was shortened to 15 min or lengthened to 48 hr. Protection due to heat shock required new protein synthesis, since it did not occur when protein or RNA synthesis inhibitors were added. By ameliorating excitotoxic processes, HSPs may attenuate brain injury in certain pathologic conditions.

'Ischemic tolerance' phenomenon detected in various brain regions

We investigated the effects of mild and non-lethal ischemic insult on neuronal death following subsequent lethal ischemic stress in various brain regions, using a gerbil model of bilateral cerebral ischemia. Single 10-min ischemia consistently caused neuronal damage in the hippocampal CA1, CA2, CA3 and CA4, layer III/IV of the cerebral cortex, dorsolateral part of the caudoputamen and ventrolateral part of the thalamus. On the other hand, in double ischemia groups, 2-min ischemic insult 2 days before 10-min ischemia exhibited significant protection in the CA1 and CA3 of the hippocampus, the cerebral cortex, the caudoputamen and the thalamus. Five-min ischemic insult 2 days before 10-min ischemia also showed protective effect in the same areas as those of 2-min ischemia except for the CA1 region of the hippocampus, while 1-min ischemic insult exhibited no protective effect in any brain regions. In the immunoblot analysis, both 2- and 5-min ischemia caused increased synthesis of heat shock protein 72 (HSP 72) in the hippocampus, but 1-min ischemia did not. The present study demonstrated that the 'ischemic tolerance' phenomenon was widely found in the brain and also suggested that ischemic treatment severe enough to cause HSP 72 synthesis might be needed for induction of 'ischemic tolerance'.

Temporal profile of the effects of pretreatment with brief cerebral ischemia on the neuronal damage following secondary ischemic insult in the gerbil: cumulative damage and protective effects

We examined the response of the gerbil brain to secondary ischemic insult following pretreatment with brief ischemia at intervals of 5 min, 1 and 6 h, 1, 2, 4, 7 and 14 days. Two minutes of bilateral carotid artery occlusion produced no histopathological brain damage, whereas 3 min of occlusion caused a moderate to severe reduction in the number of hippocampal CA1 pyramidal cells. Two-minute occlusion followed by 3-min occlusion at 5-min, 1- and 6-h intervals resulted in almost complete destruction of CA1 neurons. Additional neuronal damage was observed in the striatum at a 1-h interval and in the thalamus and the neocortex at 1- and 6-h intervals. The neuronal damage was most severe at a 1-h interval. Two-minute ischemia followed by 3-min ischemia at intervals of 1, 2, 4 and 7 days, however, caused a marked protective effect, and the hippocampal CA1 neurons were preserved. The protective effect was not observed at a 14-day interval and following pretreatment with 1-min ischemia. Thus, pretreatment with brief ischemia leads to complex responses of the brain to secondary ischemic insult; cumulative damage at intervals of 1-6 h and protective effects at intervals of 1-7 days.

Heat shock protein hsp72 induction in cortical and striatal astrocytes and neurons following infarction

Transient global and transient focal ischemia induced the 72 kDa heat shock protein (hsp72) in neurons in cortex, striatum, and other regions known to be injured during transient ischemia. A novel finding was the induction of hsp72 in islands (cylinders in three dimensions) of cells composed of astrocytes around the perimeter and neurons in the interior. Since histology showed pale staining in these regions, it is proposed that these islands represent areas of focal infarction in the distribution of small cortical and lenticulostriate arteries. Although the factors responsible for hsp72 induction during ischemia and infarction are unknown, these results suggest differences in mechanisms of hsp72 induction in astrocytes compared to neurons.

Expression of heat shock protein 70 and heat shock cognate 70 messenger RNAs in rat cortex and cerebellum after heat shock or amphetamine treatment

The expression of strictly inducible hsp70 mRNAs and constitutively expressed hsc70 mRNAs was compared in cerebellum and cerebral cortex of control rats, heat-shocked rats, and rats made hyperthermic with amphetamine. An hsc70-specific oligonucleotide probe identified a 2.55-kb mRNA in cerebellum and cerebral cortex of all rats. An hsp70-specific oligonucleotide probe identified a 3.05-kb mRNA and a 3.53-kb mRNA in cerebellum and cerebral cortex of heat-shocked and amphetamine-treated rats, but not in control rats. Quantitation demonstrated that both hsp70 and hsc70 mRNA levels, relative to 18S rRNA levels, were increased following each treatment. The relative levels of both mRNAs were higher in cerebellum than in cerebral cortex. In amphetamine-treated rats, hsc70 mRNA relative levels increased at body temperatures greater than 39 degrees C, whereas hsp70 mRNA synthesis was induced at temperatures greater than 40 degrees C. Total thermal response values and relative levels of both mRNAs were compared. The results suggested that both the transcription and turnover of hsp70 mRNAs differed between cerebellum and cerebral cortex. At equivalent total thermal response values, amphetamine-treated rats had higher relative levels of hsp70 mRNAs than heat-shocked rats, suggesting that amphetamine enhanced the induction of hsp70 mRNAs.

Postischemic spontaneous hyperthermia is not a major aggravating factor for neuronal damage following repeated brief cerebral ischemia in the gerbil

Brief and non-lethal cerebral ischemia produces most severe neuronal damage when such ischemia is induced repeatedly at 1-h intervals. We examined whether spontaneous postischemic hyperthermia is an aggravating factor for the cumulative damage following repeated ischemia in the gerbil. We maintained body and cranial temperature at normothermia throughout the initial reperfusion period, but could not observe an amelioration of histopathological brain damage following two 2-min bilateral carotid artery occlusions at a 1-h interval as compared to hyperthermic conditions. The results suggest that postischemic hyperthermia is not a major aggravating factor for the cumulative damage following repeated ischemic insults.

Hyperthermia-induced neuronal protection against ischemic injury in gerbils

We investigated the effect of hyperthermic pretreatment before induction of ischemia using a gerbil model of 5-min forebrain ischemia. A single hyperthermic treatment 18 h before ischemia exhibited a partial protective effect, and repetitive hyperthermic pretreatments at 18-h intervals before ischemia showed clear protection against neuronal death in the CA1 area of the hippocampus, whereas single hyperthermic treatment 3, 6, 24, or 50 h before ischemia exhibited little protective effect. This transient and cumulative neuroprotective effect of hyperthermic pretreatment strongly suggested the involvement of stress reactions after hyperthermia in the protective mechanism against ischemic neuronal death.

Stress protein synthesis by crayfish CNS tissue in vitro

Some crustacean axons remain functional for months after injury. This unusual property may require stress proteins synthesized by those neurons or provided to them by glial cells. To begin to explore this hypothesis, we examined the conditions that stimulated stress protein synthesis by crayfish CNS tissue in vitro. Incubation for 1-15 h with arsenite or at temperatures about 15 degrees C higher than the acclimation temperature of 20 degrees C induced transient expression of several stress proteins. The heat stress response was blocked by Actinomycin D, suggesting that synthesis of new mRNA was required. In addition, the major crayfish 66 kD stress protein and its mRNA had sequence identities with the 70 kD stress proteins of mammals. Since the crayfish stress response has much in common with that of other organisms, the unique advantages of the crayfish nervous system can be used to study the impact of stress proteins on glial and neuronal function.

Chronic cerebral intracellular alkalosis following forebrain ischemic insult in rats

We measured cerebral intracellular pH using in vivo phosphorus-31 nuclear magnetic resonance spectroscopy during 1 week after forebrain ischemia or sham operation in eight and seven rats, respectively. Mean maximum pH was significantly higher (p less than 0.003) in the ischemic group than in the sham-operated group (7.34 +/- 0.03 and 7.19 +/- 0.02, respectively). The difference between mean maximum pH and baseline pH (7.08 +/- 0.01 in each group) was significantly greater (p less than 0.02) in the ischemic group than in the sham-operated group. In the ischemic group, alkalosis occurred primarily after 48-72 hours of recirculation. We speculate that brain tissue alkalosis occurring chronically after ischemia is associated with delayed ischemic neuronal death.