A comparison of induced heat-shock protein in neurons destined to survive and those destined to die after transient ischemia in rats

Dynamic expression changes of Bcl-2, Caspase-3 and Hsp70 in middle cerebral artery occlusion rats

BACKGROUND

This study aimed to study the dynamic changes of B cell lymphoma/leukaemia 2 (Bcl-2), caspase-3 and heat shock response protein 70 (Hsp70) in blood serum following acute middle cerebral artery occlusion (MCAO) in rats.

METHODS

Occlusion of the cerebral artery was accomplished via the intraluminal filament, followed by the TTC staining evaluation and neurological deficit score. Meanwhile, the blood serum was extracted at 0.5, 2, 3, 6, 12 and 24 hours and 3 and 7 days after surgery. The serum expression levels of caspase-3, Bcl-2 and Hsp70 were determined using ELISA kits according to the manufacturer's protocols. Expression correlations between Bcl-2 and Hsp70, Bcl-2 and caspase-3 were analysed using correl function. A rats model was successfully established.

RESULTS

The expression of all three indexes, including Bcl-2, caspase-3 and Hsp70, was significantly increased after surgery (p < 0.05) and peaked at 12, 24 and 24 hours, respectively. Up to 7 days after MCAO, the expression levels of these proteins recovered to the control levels. There were positive correlations between the expressions of Bcl-2 and Hsp70, Bcl-2 and caspase-3 (p < 0.05).

CONCLUSIONS

The altered expressions of these proteins in the blood serum may result in many symptoms in acute ischaemic stroke individuals.

Cerebral neurons of transgenic ALS mice are vulnerable to glutamate release stimulation but not to increased extracellular glutamate due to transport blockade

Mechanisms of motor neuron loss in amyotrophic lateral sclerosis (ALS) are unknown, but it has been postulated that excitotoxicity due to excessive glutamatergic neurotransmission by decreased efficiency of glutamate transport may be involved in both familial (FALS) and sporadic ALS. Using microdialysis in vivo, we tested the effects of the glutamate transport inhibitor L-trans-pyrrolidine-2,4-dicarboxylate (PDC) and of 4-aminopyridine (4-AP), which stimulates glutamate release from nerve endings, in the hippocampus and motor cortex of wild type (WT) and transgenic SOD1/G93A mice, an established model of FALS. Perfusion of 4-AP induced convulsions, expression of the inducible stress-marker heat-shock protein 70 (HSP70) and hippocampal neuronal loss. These effects were similar in both WT and G93A mice, and, in both groups, they were prevented by the previous systemic administration of the NMDA receptor antagonist MK-801. In contrast, perfusion of PDC resulted in a large and long-lasting (2 h) increase of extracellular glutamate, but no convulsions, neuronal damage or HSP70 expression were observed in either the WT or the G93A mice. Our results demonstrate that SOD1 G93A mutation does not enhance the vulnerability to endogenous glutamate-mediated excitotoxicity in brain, neither by blocking glutamate transport nor by stimulating its release. Therefore, these data do not support the possibility that glutamate transport deficiency may be an important factor of brain neuronal degeneration in familial ALS.

LateN-methyl-d-aspartate receptor blockade rescues hippocampal neurons from excitotoxic stress and death after 4-aminopyridine-induced epilepsy

The intrahippocampal perfusion of 4-aminopyridine (4-AP) in the rat produces immediate seizures and delayed neuronal death, due to the overactivation of N-methyl-D-aspartate (NMDA) receptors by endogenous glutamate released from nerve endings. With the same time course, 4-AP also induces the expression of the cell stress marker heat shock protein 70 (HSP70) in the contralateral non-damaged hippocampus. We have used this experimental model to study the mechanisms of the delayed neuronal stress and death. The NMDA receptor antagonist (+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclohepten-5,10-imine maleate (MK-801), administered intraperitoneally 30 or 60 but not 120 min after 4-AP perfusion, when animals show intense electroencephalography epileptiform activity, prevented the delayed neurodegeneration whereas the seizures continued for about 3 h as in the control animals. With an identical time window, MK-801 treatment also modified the pattern of HSP70 expression; the protein was expressed in the protected perfused hippocampus but no longer in the undamaged contralateral hippocampus. The possible role of Ca2+ in the delayed cell death and HSP70 expression was also studied by coperfusing the intracellular Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid tetrakis(acetoxymethyl ester) with 4-AP. This treatment resulted in protective and HSP70 effects very similar to those of MK-801. These results suggest that the seizures are not linked to neurodegeneration and that NMDA receptors need to be continuously overactivated by endogenous glutamate for at least 60 min in order to induce delayed neuronal stress and death, which are dependent on Ca2+ entry through the NMDA receptor channel.

Expression of heat shock protein 70 induced by 4-aminopyridine through glutamate-mediated excitotoxic stress in rat hippocampus in vivo

The intrahippocampal administration of 4-aminopyridine (4-AP) induces epileptic seizures and neurodegeneration, due probably to stimulation of glutamate release from synaptic terminals. We have studied the time course of the neurodegenerative changes produced by 4-AP, perfused through microdialysis cannulas in rat hippocampus, and correlated them with the expression of the inducible heat shock protein 70 (HSP70), detected immunocytochemically. Electroencephalographic seizure activity appeared immediately after the beginning of 4-AP perfusion. The first signs of histological neuronal damage were observed in CA1 and CA3 subfields of the perfused hippocampus 3 h after treatment and progressed until reaching a maximal neuronal loss at 24 h. In 4-AP-treated rats HSP70 was expressed mainly in neurons of the contralateral hippocampus, with a time course and cellular distribution very similar to the neurodegeneration observed in the perfused hippocampus, but no neuronal damage was observed. The N-methyl-D-aspartate (NMDA) receptor antagonists MK-801 and (3-phosphonopropyl)-piperazine-2-carboxylic acid prevented the seizures, the neurodegeneration and the expression of HSP70. These data demonstrate that the 4-AP-induced release of endogenous glutamate overactivates NMDA receptors in the perfused hippocampus and that the resulting neuronal hyperexcitability propagates to the contralateral hippocampus, generating a glutamate-mediated neuronal stress sufficient to induce the expression of HSP70 but not to produce neurodegeneration. These findings provide a useful model for investigating the relationships between neuronal hyperexcitation, neurodegeneration and the role of HSP expression.

Sequential expression patterns of apoptosis- and cell cycle-related proteins in neuronal response to severe or mild transient hypoxia

Severe hypoxia was shown to induce apoptotic death in developing brain neurons, whereas mild hypoxia was demonstrated to stimulate neurogenesis. Since the apoptotic process may share common pathways with mitosis, expression profiles of proteins involved in apoptosis or the cell cycle were analyzed by immunohistochemistry and/or western blotting, in relation with cell outcome of cultured neurons from fetal rat forebrain subjected to either lethal (6 h) or non-lethal (3 h) hypoxia (95% N(2)/5% CO(2)). Hypoxia for 6 h led to apoptosis that was inhibited by the cell cycle blocker olomoucine. Transient overexpression of proliferating cell nuclear antigen was followed by increasing expression of p53, p21, Bax and caspases, whereas Bcl-2 and heat shock proteins were progressively repressed. Conversely, a 3-h hypoxic insult initiated neuronal mitosis, with increased thymidine incorporation. In these conditions, levels of proliferating cell nuclear antigen, Rb, Bcl-2 and heat shock proteins were persistently elevated, while expression of p53, p21, Bax and caspases gradually decreased. These data confirm that hypoxia promotes cell cycle activation, whatever the stress intensity. This process is then aborted following apoptosis-inducing hypoxia, whereas sublethal insult would trigger neurogenesis, at least in developing brain neurons in vitro, by stimulating timed expression of neurogenic and survival-associated proteins.

Temporospatial expression of HSP72 and c-JUN, and DNA fragmentation in goat hippocampus after global cerebral ischemia

The role of gene induction (expression of HSP72 and c-JUN proteins) and delayed ischemic cell death (in situ labeling of DNA fragmentation) have been investigated in the goat hippocampus after transient global cerebral ischemia. The animals were subjected to 20-min ischemia (bilateral occlusion of the external carotid arteries plus bilateral jugular vein compression) and allowed to reperfuse for 2 h, and then 1, 3, and 7 days. Histological signs of cell loss were not found in the hippocampus at 2 h, 1 day, or 3 days of reperfusion. However, such an ischemic insult produced extensive, selective, and delayed degeneration in the hippocampus, as 68% of the neurons in CA1 had died at 7 days, but cell loss was not detected in CA3 and dentate gyrus fields. Concomitantly, a high percentage of TUNEL-positive CA1 neurons (60+/-9%, mean +/- SEM) was seen at 7 days, but not at the earlier time points. Mild induction of HSP72 was detected in the goat hippocampus after ischemia. The maximum percentage of HSP72-positive neurons (10-15%) was shown at 3 days of reperfusion and was concentrated mainly in the CA3 field, subiculum, and hilus, rather than in the CA1 field, whereas HSP72 expression was hardly detected at 7 days. At this later time point, scattered induction of nuclear c-JUN was found in a few neurons. The results show that: 1) postischemic delayed neuronal death selectively affects the CA1 field in the goat hippocampus, a phenomenon which seems to take longer to develop than in previously reported rodent models; and 2) postischemic expression of c-JUN does not appear to be related to cell death or survival, while the inability of most CA1 neurons to express HSP72 could contribute to neuronal death.

Hyperthermic preconditioning protects against spinal cord ischemic injury

BACKGROUND

Paraplegia can result from operations requiring transient occlusion of the descending thoracic aorta. The present study tested whether inducing hyperthermia in rats before aortic ischemia would be neuroprotective.

METHODS

Rats were randomly assigned to hyperthermic preconditioning (n = 27) or control (n = 32) groups. Eighteen hours before ischemia, the hyperthermic preconditioned rats were heated at 41 degrees C for 15 minutes. Ten minutes of spinal ischemia were produced by balloon occlusion of the thoracic aorta. Neurologic performance scores were evaluated daily to 7 days after ischemia. The lumbar region of the spinal cord was removed for histologic grading.

RESULTS

The hyperthermic preconditioned animals had less permanent spinal cord injury compared with controls (29.6% versus 59.4%, p = 0.02), and the incidence of immediate paraplegia in the hyperthermic preconditioned group was significantly less than that in the control group (3.7% versus 28.1%, p = 0.03). Histologic scores correlated with the neurologic outcome at the time of sacrifice in rats with permanent spinal cord injury but not in those walking normally.

CONCLUSIONS

We used a rat model of spinal cord ischemia and found that hyperthermic preconditioning before spinal cord ischemia resulted in improved clinical outcome.

Time course of brain neuronal degeneration and heat shock protein (72) expression following neck tourniquet-induced cerebral ischemia in the rat

1. The present study was designed to examine the regional expression of HSP72/73 protein after a 7.5-min period of cerebral ischemia and to compare the distribution of HSP neurons with the localization of irreversible neuronal degeneration as analyzed by silver impregnation technique. 2. During 6-24 hr after cerebral ischemia clear-cut neuronal argyrophilia developed in several brain regions including the hippocampal hilus, nucleus reticularis thalami, and colliculi inferiores. With the exception of the hippocampal hilus, the structures which showed silver impregnability were HSP72 negative at 6-24 hr. 3. Despite the clear HSP72 expression seen in hippocampal CA1 neurons, a significant loss of these neurons was seen at 7 days after ischemia. 4. These data show that in some structures the presence of HSP72 is indicative of higher resistance of these neurons to ischemia-induced degeneration, however, the process of delayed neuronal degeneration appears to be independent of the accelerated synthesis of HSP72 seen during the early period of reflow.

Benign focal ischemic preconditioning induces neuronal Hsp70 and prolonged astrogliosis with expression of Hsp27

We have established a focal preconditioning (PC) paradigm that produces significant and prolonged ischemic tolerance (IT) of the brain to subsequent permanent middle cerebral artery occlusion (MCAO). PC using 10 min of MCAO induces brain tolerance at 1-7 days of reperfusion that requires active protein synthesis. The protective protein(s) involved are unknown. In these studies the increased transcription and translation of the inducible 70-kDa heat shock protein (Hsp70) and the 27-kDa heat shock protein (Hsp27), and astrogliosis/glial fibrillary acidic protein (GFAP) were determined by Northern analysis and immunohistochemistry following PC. Cellular localization of proteins was determined by double labeling. PC produced no brain injury but did increase Hsp70 mRNA transiently at 6 h and increased Hsp27 mRNA later at 24 h for at least 5 days. Protein expression induced by PC exhibited a similar profile. Hsp70 protein was primarily expressed in neurons from 1 to 5 days post-PC throughout the PC cortex. Hsp27 protein expression was initiated later for a much longer period of time. A remarkable astroglyosis was verified with increased astrocytic Hsp27 from 1 to 7 days after PC. Gliosis with increased Hsp27 in the PC cortex was still present but reduced 4 weeks after PC. Therefore, PC that results in brain tolerance/neuroprotection increases neuronal Hsp70 in the PC cortex and activated astrocytic Hsp27 in the PC cortex in a temporal fashion associated with developing IT. The short duration of benign ischemia (PC) that produces IT produces a robust, long-lived cellular and protein synthetic response that extends throughout the entire cortex (i.e. well beyond the MCA perfusion territory). The resulting IT is associated with changes in astrocyte-activation that might provide increased support and protection from injury. Although both Hsp70 and Hsp27 may participate in the neuroprotection/brain tolerance induced by PC, the temporal expression patterns of these proteins indicate that they are not solely responsible for the tolerance to brain injury.

Preischemic blood glucose supply to the brain modulates HSP(72) synthesis and neuronal damage in gerbils

Preischemic hyperglycemia is known to aggravate brain damage caused by transient forebrain ischemia. Because heat shock proteins (HSPs) 72 have been proposed to play a protective role against ischemic neuronal injury, we studied the HSP(72) mRNA expression and protein synthesis in gerbils subjected to 10 min bilateral carotid occlusion under normoglycemic, hyperglycemic and fasting conditions. HSP(72) mRNA expression and HSP(72) synthesis were studied using in situ hybridization and immunostaining, respectively. After 8 h of blood recirculation, HSP(72) mRNAs were expressed in all the hippocampal subfields of the three different groups, with higher expression in the hyperglycemic gerbils. After 48 h of reperfusion, HSP(72) mRNAs had almost completely disappeared in the hyper- and normoglycemic groups, and were more strongly expressed in the CA(1) neurons of the fasted group. At this time, fasted gerbils exhibited intense HSP(72) immunoreactivity in the CA(1), whereas an absence of immunoreactivity was observed in that area in the other groups. Finally, ischemia was also associated with marked astrocytic activation, as evidenced by GFAP immunostaining. Overall results indicate that preischemic differences in blood glucose supply to the brain are related to HSP(72) mRNA expression (in terms of duration) and to HSP(72) protein induction (in terms of intensity) in the vulnerable CA(1) neurons of the hippocampus. Ability of CA(1) neurons to synthesize HSP(72) proteins was associated with higher neuronal survival in the fasted group after 48 h of reflow, suggesting a protective role of HSP(72), even though evaluation of neuronal damage at 7 days indicated that neuronal death was mainly delayed in the time.

Pentylenetetrazol seizures induce cell suffering but not death in the immature rat brain

To investigate whether long-term functional consequences of status epilepticus (SE) induced by pentylenetetrazol in 10-day-old rats correlated with cell injury and/or death, acid fuchsin and TUNEL staining were performed between 4 to 144 h after SE. Acid fuchsin stained hippocampus, amygdala and cerebral cortex at 24 h but not at 72 and 144 h. No DNA fragmentation was apparent at any time. Thus, immature neurons subjected to sustained seizures suffer transiently but survive probably by activating repair processes.

Pixel-based image analysis of HSP70, GADD45 and MAP2 mRNA expression after focal cerebral ischemia: hemodynamic and histological correlates

Gene expression studies with in situ hybridization after focal brain ischemia indicate a variety of distinct anatomical patterns. An important question is to what extent such reactive gene expression correlates with neuronal damage or survival. To study these questions, we focused on two stressed-induced genes, heat shock protein 70 (HSP70) and growth-arrest and DNA damage-inducible gene (GADD) 45 mRNA, and we compared reactive changes in mRNA to loss of the constitutive signal for microtubule-associated protein 2 (MAP2) mRNA. A pixel-based image analysis of mRNA signals was carried out using a highly reproducible model of focal brain ischemia. A poly-l-lysine coated filament was used to occlude the origin of the middle cerebral artery (MCA) for 2 h in ventilated, normothermic rats. Brains were collected after 0, 1, 3 and 6 h, and 1, 3 and 7 days. In situ hybridization analysis was carried out for HSP70 mRNA, GADD45 mRNA and MAP2 mRNA. Autoradiographic data sets were averaged and co-mapped into a common template of the rat brain. These data sets were then compared on a pixel-by-pixel basis with previously acquired image data sets derived from quantitative studies of local cerebral blood flow (LCBF) (obtained at the end of 2-h ischemia) of and infarctive histopathology (obtained at 3 days) in the same focal ischemia model. HSP70 mRNA and GADD45 mRNA were grossly elevated in the hemisphere subjected to ischemia during the first day. Pixel-based analysis showed a strong correlation between HSP70 mRNA signals, the degree of early blood-flow reduction and the probability of histological infarction. GADD45 mRNA was expressed in a more variable fashion. Decreases in MAP2 mRNA signals at 1, 3 and 7 days correlated strongly with histological infarction. These co-mapping procedures allow us to conclude that HSP70 mRNA is a robust indicator of ischemic stress and histological outcome after 2 h of focal brain ischemia. The topographic features of GADD45 expression suggest its possible role in conferring resistance to ischemic injury. Finally, our results indicate that local decreases in constitutive MAP2 expression at 1 day and beyond may be used as a robust marker of tissue regions having a high probability of focal infarction.

C-Fos, Jun D and HSP72 immunoreactivity, and neuronal injury following lithium-pilocarpine induced status epilepticus in immature and adult rats

In order to follow the maturation-related evolution of neuronal damage, cellular activation and stress response subsequent to Li-Pilo seizures in the 10- (P10), 21-day-old (P21) and adult rat, we analyzed the expression of the c-Fos protein as a marker of cellular activation, HSP72 immunoreactivity as the stress response and silver staining for the assessment of neuronal damage in 20 selected brain regions. The early wave of c-Fos measured at 2 h after the onset of seizures was present in most structures of the animals at the three ages studied and particularly strong in the cerebral cortex, hippocampus and amygdala. The late wave of c-Fos measured at 24 h after the onset of seizures and that was shown to correlate to neuronal damage was absent from the P10 rat brain, and present mainly in the cerebral cortex and hippocampus of P21 and adult rats. The expression of the stress response, assessed by the immunoreactivity of HSP72 at 24 h after the seizures was absent from the P10 rat brain and present in the entorhinal cortex, amygdala, hippocampus and thalamus of P21 and adult rats. The expression of Jun D at 24 h after the seizures was discrete and present in most brain regions at all ages. Neuronal injury assessed by silver staining at 6 h after the onset of seizures was very discrete in the brain of the P10 rat and limited to a few neurons in the piriform and entorhinal cortices. In older animals, marked neuronal degeneration occurred in the cerebral cortex, amygdala, hippocampus, lateral septum and thalamus. Thus the immediate cell activation induced by lithium-pilocarpine seizures which is present at all ages translates only into a late wave of c-Fos and the expression of HSP72 in P21 and adult animals in which there will be extensive cell damage.

Neuronal stress response and neuronal cell damage after cardiocirculatory arrest in rats

Cardiocirculatory arrest is the most common clinical cause of global cerebral ischemia. We studied neuronal cell damage and neuronal stress response after cardiocirculatory arrest and subsequent cardiopulmonary resuscitation in rats. The temporospatial cellular reactions were assessed by terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end-labeling (TUNEL) staining of DNA fragments, in situ hybridization (heat shock protein hsp70; immediate early genes c-fos and c-jun), and immunocytochemical (HSP70; and myeloperoxidase, specific marker of polymorphonuclear leukocytes [PMNL]) techniques. Cardiac arrest of 10 minutes' duration was induced in mechanically ventilated male Sprague-Dawley rats anesthetized with nitrous oxide and halothane. After cardiopulmonary resuscitation, animals were allowed to reperfuse spontaneously for 6 hours, 24 hours, 3 days, and 7 days (n = 6 per group). Five sham-operated animals were controls. The TUNEL staining revealed an early onset degeneration in the thalamic reticular nucleus (TRN) at 6 hours that peaked at 3 days. In contrast, degeneration was delayed in the hippocampal CA1 sector, showing an onset at 3 days and a further increase in the number of TUNEL-positive cells at 7 days. A minor portion of TUNEL-positive nuclei in the CA1 sector showed condensed chromatin and apoptotic bodies, whereas all nuclei in the TRN revealed more diffuse staining. After 6 hours of reperfusion, levels of mRNA for hsp70 and c-jun were elevated in circumscribed areas of cortex, in all hippocampal areas, and in most nuclei of thalamus, but not in the TRN. After 24 hours, a strong expression of mRNA for hsp70 and c-jun could be observed in the second layer of the cortex and in hippocampal CA1 sector; hsp70 also was observed in hippocampal CA3 sector. Some animals showed expression of hsp70 and c-jun in the dentate gyrus. After 3 days, hsp70 and c-jun were detected mainly in the CA1 sector of hippocampus. At 7 days, mRNA for both returned to control values. Therefore, delayed cell degeneration in the CA1 sector corresponds to a prolonged expression of hsp70 and c-jun in this area. In situ hybridization studies for c-fos revealed a strong signal in CA3 and dentate gyrus and a less prominent signal in TRN at 6 hours. At 24 hours, CA4 and amygdalae were positive, whereas at 3 and 7 days, the signal reached control levels; no prolonged or secondary expression was observed in the CA1 sector. Immunohistochemical study confirmed translation of HSP70 in various areas corresponding to the detection of mRNA, including the CA1 sector. The number of PMNL increased significantly at 6 hours and 7 days after cardiac arrest; PMNL were distributed disseminately and were not regionally associated with neuronal cell damage. The current data support the view that CA1 neurons might undergo an apoptosis-associated death after cardiac arrest, but PMNL are not directly involved in this process. The marked differences in the time course and the characteristics of TUNEL staining and the neuronal stress response in CA1 sector and TRN point to different mechanisms of neuronal injury in the two selectively vulnerable areas.

Induction of Apg-1, a member of the heat shock protein 110 family, following transient forebrain ischemia in the rat brain

Apg-1 (Osp94) and apg-2 belong to the heat shock protein (hsp) 110 family. In mouse somatic cells the apg-1 and hsp105/110 transcripts are inducible by a 32 degrees C to 39 degrees C heat shock, while apg-2 is not heat-inducible. Since ischemia is known to induce expression of hsp70, its effect on expression of apg-1 was assessed by using the 20-min forebrain ischemia model of the rat. In the cerebral cortex, Northern blot analysis and in situ hybridization histochemistry demonstrated an increased expression in neuronal cells of apg-1 transcripts 3 h after the onset of reperfusion, with a peak at 12 h, followed by a decline. In the hippocampus, the level was increased at 3 h, remained constant until 24 h, and then declined. Transcript levels of apg-2 as well as hsp 105 were also increased under the present conditions, indicating that the expression of apg-2 was differentially regulated in response to heat and ischemic stresses. The induction kinetics of hsp 105, but neither apg-2 nor hsp 70, were identical to those of apg-1. These results demonstrated that brain ischemia/reperfusion induced expression of each member of the hsp 110 family, although the regulatory mechanisms may not be the same. They also suggest a significant role of apg-1 in both the ischemic- and heat-stress responses and in the normal functioning of the non-stressed neuronal cells.

Spatial and temporal evolution of neuronal activation, stress and injury in lithium-pilocarpine seizures in adult rats

In order to follow the spatial and temporal evolution of neuronal damage, cellular activation and stress responses subsequent to lithium-pilocarpine seizures of various durations in the adult rat, we analyzed the expression of Fos protein and local cerebral glucose utilization as markers of cellular activation, HSP72 immunoreactivity and acid fuchsin staining as indicators of cellular stress and injury, and Cresyl violet staining for the assessment of neuronal damage. The expression of Fos appeared very early, 2-30 min after the onset of polyspikes and intensified during the following 4 h. Fos immunoreactivity was especially high in the hippocampus, cerebral cortex, amygdala and anterior olfactory nuclei. Local cerebral glucose utilization measured during the second hour of seizures was largely increased (350-580%) over control levels in cortical areas, amygdala, dentate gyrus, caudate nucleus and mediodorsal thalamus. HSP72 immunoreactivity never appeared earlier than 40-50 min after the onset of polyspikes, and was most prominent in hippocampal CA3 area, cerebral cortex (except the piriform cortex) and anterior olfactory nuclei. Acid fuchsin staining was maximal in the piriform cortex and the polymorphic layer of the dentate gyrus. Staining was moderate in the sensorimotor cortex and the amygdala. Neuronal damage was extensive in the piriform and entorhinal cortices, the hippocampal CA3 area and the polymorphic layer of the dentate gyrus, basal amygdala, mediodorsal thalamus and anterior olfactory nuclei. In conclusion, the present study shows that brain regions with the highest expression of Fos and the largest metabolic activation were also highly stained with acid fuchsin and most heavily damaged. Conversely, there is no clear relationship between HSP72 expression, cellular activation and neuronal damage.

Induction of heme oxygenase protein protects neurons in cortex and striatum, but not in hippocampus, against transient forebrain ischemia

To clarify whether heme oxygenase-1 (HO-1) protein plays a protective role against cerebral ischemia, we investigated the effects of an HO inhibitor (tin mesoporphyrin IX [SnMP] three doses of 30 micromol/kg, intraperitoneally) and an HO inducer (hemin, three doses of 30 micromol/kg, intraperitoneally) on the pathologic outcome and on the immunohistochemical reaction for HO-1 after 20-minute transient forebrain ischemia followed by 3-day reperfusion in rats. Hemin significantly increased viable neurons in the cortex (compared to the SnMP-treated group, P < .05) and striatum (compared to the saline-treated group at P < .01 and SnMP-treated group at P < .05), and intense HO-1 immunoreactivity was observed in cortex and striatum, whereas the administration of SnMP tended to decrease viable neurons in the parietal cortex. In contrast, neither hemin nor SnMP affected the pathologic outcome in the CA1 and CA3 hippocampi, in which HO-1 immunoreactivity was weak. These results suggest that induction of HO-1 protein may contribute to cellular defense against ischemic damage in brain regions where potential ability to synthesize HO-1 is retained in ischemia.

Effects of pentylenetetrazol-induced status epilepticus on c-Fos and HSP72 immunoreactivity in the immature rat brain

Pentylenetetrazol (PTZ)-induced status epilepticus (SE) leads to acute and long-term metabolic decreases in specific brain regions of rats at 10 (P10) or 21 days after birth (P21). These decreases are not related to apparent neuronal damage. Therefore, to better understand the neuronal activation and stress response to PTZ in immature rats, we mapped the expression of c-Fos and of the 72 kDa heat-shock protein (HSP72) in the same model of severe SE induced by the repetitive i.p. injections of subconvulsive doses of PTZ. Rats were sacrificed either at 2 or 24 h after the onset of SE in order to reveal c-Fos immunoreactivity, and at 24 and 72 h for HSP72 expression. Hematoxylin-eosin staining was performed at 24, 72 and 144 h after SE. The expression of c-Fos at 2 h after SE was more marked at P21 than at P10 and was prominent at both ages in the hippocampal dentate gyrus, cerebral cortex and amygdala. Some immunoreactivity was also present in the hypothalamus, thalamus and a few brainstem and cerebellar regions at both ages. There was a good relation between the regions expressing c-Fos and those exhibiting acute metabolic decreases at P21. Conversely, PTZ seizures did not lead to any expression of c-Fos at 24 h after SE or of HSP72 at 24 or 72 h at any age. Cell density was not affected by PTZ-induced SE at any age and at any time. These results suggest that c-Fos is a useful marker of neuronal activation induced by severe and prolonged seizures in the immature brain. The lack of HSP72 and of late c-Fos expression likely reflect the absence of neuronal damage in this model of PTZ-induced SE in the immature rat.

Sequence of neuronal responses assessed by immunohistochemistry in the newborn rat brain after hypoxia-ischemia

OBJECTIVE

Our purpose was to study the neuronal responses of heat shock protein-72 (a stress-inducible protein) and microtubule-associated protein-2 (a constitutive protein of the neuronal cytoskeleton) after hypoxia-ischemia and their relationship with permanent damage in the newborn rat brain.

STUDY DESIGN

Seven-day-old rats were exposed to unilateral carotid artery ligation followed by 2 hours of hypoxia (8% oxygen/92% nitrogen) and then killed at time points ranging from 1 to 72 hours after injury. Brains were removed for immunohistochemical and routine staining.

RESULTS

Heat shock protein-72 appearance and microtubule-associated protein-2 disappearance occurred from 1 hour after injury, mainly in the dentate gyrus of the hippocampal formation and the cerebral cortex. Such alterations reached maximal levels at 24 hours for both proteins. Microtubule-associated protein-2 staining recovered in almost all parts of the brain. However, the hippocampal CA3 showed a delay in the responses for both proteins, and microtubule-associated protein-2 did not recover the response to immunostaining. Histologic evaluation at 72 hours after hypoxia by routine methods showed predominant damage in the hippocampal CA3.

CONCLUSION

Our results show that delayed responses of heat shock protein-72 and microtubule-associated protein-2 are related to a high incidence of neuronal cell loss in the hippocampal CA3 region.

The heat shock stress response after brain lesions: induction of 72 kDa heat shock protein (cell types involved, axonal transport, transcriptional regulation) and protein synthesis inhibition

The cerebral stress response is examined following a variety of pathological conditions such as focal and global ischemia, administration of excitotoxins, and hyperthermia. Expression of 72 kDa heat shock protein (Hsp70) and hsp70 mRNA, the mechanism underlying induction of hsp70 mRNA involving activation of heat shock factor 1, and inhibition of cerebral protein synthesis are different aspects of the stress response considered here. The results are compared with those in the literature on induction, transcriptional regulation, expression, and cellular location of Hsp70, with a view to getting more insight into the function of the stress response in the injured brain. The present results illustrate that Hsp70 can be expressed in cells affected at various degrees following an insult that will either survive or dic as the brain lesion develops, depending on the severity of cell injury. This indicates that, under certain circumstances, synthesized Hsp70 might be necessary but not sufficient to ensure cell survival. Other situations involve uncoupling between synthesis of hsp70 mRNA and protein, probably due to very strict protein synthesis blockade, and often result in cell loss. Cells eventually will die if protein synthesis rates do not go back to normal after a period of protein synthesis inhibition. The stress response is a dynamic event that is switched on in neural cells sensitive to a brain insult. The stress response is, however, tricky, as affected cells seem to need it, have to deal transiently with it, but eventually be able to get rid of it, in order to survive. Putative therapeutic treatments can act either selectively, potentiating the synthesis of Hsp70 protein and recovery of protein synthesis, or preventing the stress response by deadening the insult severity.

The model of pentylenetetrazol-induced status epilepticus in the immature rat: short- and long-term effects

In order to assess acute, short and long-term effects of seizures in the immature rat brain, we studied the metabolic, circulatory and histopathological changes induced by pentylenetetrazol (PTZ) given at postnatal day 10 (P10) or 21 (P21). Seizures were induced by repetitive subconvulsive injections of PTZ given as a first dose of 40 mg/kg followed 10 min later by 20 mg/kg. Thereafter, rats received every 10 min additional injections of PTZ 10 mg/kg until the onset of status epilepticus. Local cerebral metabolic rates for glucose (LCMRglc) were measured both during the seizures in P10 and P21 rats and in the young adult animal at P60 by means of the quantitative 2-deoxyglucose technique. Rates of local cerebral blood flow (LCBF) were determined during the seizures by the iodoantipyrine technique. Short-term histological changes were assessed by acid fuchsin and hematoxylin-eosin staining and by HSP72 immunohistochemistry. At P10, LCMRglcs uniformly increased (38-400%) over control values during seizures. At P21, metabolic increases (39-181%) occurred only in 20% of the structures while LCMRglcs decreased in most cortical, hippocampal and sensory areas as well as in mammillary body, discrete thalamic nuclei and white matter areas. At P10, LCBF rose (32-184%) in all brain structures whereas, at P21, LCBF decreased in cortical, hippocampal and sensory regions and increased in most other areas. At P60, in animals having seized at either age, significant long-term decreases in LCMRglcs were recorded in hippocampus, auditory and piriform cortex, medial geniculate body and mammillary body. In P60 animals exposed to PTZ at P10, LCMRglcs were also decreased in 3 other sensory areas. In P60 animals exposed to seizures at P21, LCMRglcs were additionally decreased in sensory regions, cortices, thalamic and hypothalamic regions. Neuronal cells were transiently stained with acid fuchsin, with a peak occurring at 24 h after the seizures. The stain was visible in all regions of cerebral cortex and hippocampus and in some thalamic and hypothalamic nuclei. This transient staining was not accompanied by cell degeneration as assessed by hematoxylin-eosin histology. No HSP72 expression could be detected 24 h after the seizures, neither at P10 nor at P21. The present study shows that the immature rat neurons undergo altered metabolic rates and local circulatory decreases in the acute phase, a change in the affinity of acid fuchsin as a short-term effect and long-term metabolic decreases. All these changes are located in the same regions, i.e., cerebral cortex, hippocampus, sensory regions as well as scattered thalamic and hypothalamic nuclei. Thus, short- and long-term metabolic changes induced by seizures can be used as an index of cell stress in the immature rat brain. Since all these changes occur in the absence of visible neuronal death, they might be related to changes in the final arborization and synaptic organization of the developing brain.

Expression of heat shock protein-70 and limbic seizure-induced neuronal death in the rat brain

The effect of MK-801, a non-competitive N-methyl-D-aspartate (NMDA) antagonist, on the kainic acid-induced expression of the inducible heat shock protein 70 kDa (HSP70) and on neuronal death in the rat hippocampus was investigated. HSP70 is expressed in approximately 80% of the pyramidal neurons in the CA1 field 1 day after kainic acid injection. The majority of these HSP70-immunopositive neurons exhibited swelling and a hollow appearance in the perikaryon, indicating that they had been injured following kainic acid-elicited limbic seizures. Four days after administration of kainic acid, 87% of the pyramidal neurons in the CA1 field were dead. When a single dose of MK-801 was administered 1 h before kainic acid injection, the number of rats suffering with seizures was reduced, the severity of limbic seizures was attenuated and seizure onset was delayed. Neither HSP70 expression on day 1 nor neuronal loss on day 4 in the CA1 pyramidal cell layer was observed in these animals. A considerable number of HSP70-immunopositive neurons was detected in the dentate hilus, however, and somewhat fewer in the CA3a and CA3c subfields on day 1. Severe neuronal damage in these regions followed on day 4. Interestingly, little HSP70 expression or neuronal loss was observed in the CA3b subfield in these same animals. When a single dose of MK-801 was given 4 h after kainic acid treatment, HSP70 expression was partially blocked; 18% of neurons expressed HSP70 on day 1 and 37% on day 4 in CA1 pyramidal neurons in comparison to the kainic acid controls. About 50% neuronal death was detected in the CA1 pyramidal cell layer 4 days after kainic acid treatment followed by MK-801. When the animals were treated with MK-801 4 h after kainic acid treatment followed by additional daily administration for 3 days, a negligible number of pyramidal neurons expressed HSP70, and the survival of pyramidal cells was significantly increased in the CA1 field. Limbic seizure-induced HSP70 expression not only indicates neuronal injury in the pyramidal cell layer of the hippocampus but also predicts delayed neuronal death, at least in the case of the CA1 field of animals that suffered stage IV-V seizures.

Cyclin D1 messenger RNA is induced in microglia rather than neurons following transient forebrain ischaemia

Following 30 min of forebrain ischaemia in the rat, delayed neuronal death occurs in the CA1 sector of the hippocampus within two to three days, whereas neurons in other selectively vulnerable regions, such as the dorsolateral striatum, die within 6-12 h. In this study, we investigated cyclin D1 expression, which codes for a regulatory protein in cell cycle regulation, but it is also induced in sympathetic neurons undergoing programmed cell death. Cyclin D1 messenger RNA could not be detected by in situ hybridization techniques in brains of control rats, but was found at one and two days after ischaemia in regions of the dorsolateral striatum with neuronal degeneration. DNA fragmentation in this region, identified by the terminal transferase biotinylated-UTP nick end labelling (TUNEL) procedure, was observed from 6 h after ischaemia onward. In the hippocampus, increased levels of cyclin D1 messenger RNA were found at two and three days after ischaemia in the striatum pyramidale of the CA1 sector. This expression was associated with the occurrence of neuronal damage and TUNEL-stained neurons. By seven days cyclin D1 messenger RNA was found in hardly any brain structure. There was no temporospatial overlap of cyclin D1 expression with the expression of the immediate-early genes c-fos, c-jun, and mkp-1, a result which is clearly distinct from findings in sympathetic ganglion neurons undergoing programmed cell death. These results do not suggest a role for cyclin D1 in neuronal cell death following transient forebrain ischaemia. The similarity of the cyclin D1 expression profile with that of the microglia-specific CR3 complement receptor beta-subunit messenger RNA, and the results of combined in situ hybridization and microglia-specific immunohistochemistry suggest that microglia are the source of cyclin D1 messenger RNA in the postischaemic brain. Since cyclin D1 codes for a critical regulatory protein for progression of the G0 to G1 phase in the cell cycle and we did not observe prominent occurrence of DNA fragmentation in microglial cells in the hippocampus at time points when cyclin D1 messenger RNA was found, we suggest that cyclin D1 induction is involved in the onset of microglial cell proliferation.

Molecular correlates of delayed neuronal death following transient forebrain ischemia in the rat

Following transient forebrain ischemia selective and delayed neuronal degeneration occurs in the CA1 sector of the hippocampus. It is presently unclear whether this cell death is related to programmed cell death (PCD), which occurs in neurons during development of the CNS. Recently, the expression of various genes, such as c-fos, c-jun mkp-1, cyclin D1, and hsp70 was found to be associated with PCD in model systems. We and others have described that these genes are also upregulated in the hippocampus following ischemia. Most notably, c-fos, c-jun, and hsp70 are expressed specifically in CA1 neurons at survival times shortly preceding cell degeneration in rat models of global ischemia. In addition, the gene products could be detected by immunohistochemical methods, despite a general impairment of protein synthesis. These finding are especially relevant, since recent report suggests a functional role for Fos family proteins and c-jun in PCD in neurons of the superior cervical ganglion. These results could be indicative for the occurrence of a PCD-related program in CA1 neurons ad corroborate several other lines of evidences, such as occurrence of DNA fragmentation. Clearly, further studies are necessary to elucidate the functional role of the gene inductions following ischemia in vivo.

NMDA receptors mediate heat shock protein induction in the mouse brain following administration of the ibotenic acid analogue AMAA

Expression of inducible heat shock protein-70 (HSP-70) and hsp-70 mRNA were studied in the adult mouse brain following systemic administration of the ibotenic acid analogue (+/-)-2-amino-3-hydroxy-5-methyl-4-isoxazoleacetic acid (AMAA), which is a potent N-methyl-D-aspartate (NMDA) agonist. At the dose of 20 mg/kg, AMAA produced excitatory behaviours in adult mice but overt convulsions were not seen. This treatment did not result in any detectable morphological brain damage at 4 days following administration. At 2.5 h and 5 h following treatment induction of hsp-70 mRNA expression was found in the pyramidal cell layers of CA1 and, to a lesser extent, CA3 fields of hippocampal Ammon's horn, amygdala, olfactory lobes, tenia tecta, hypothalamic nuclei and a superficial layer of cingulate, frontal and retrosplenial cortices. The presence of HSP-70 was detected by immunochemistry at 24 h following drug administration in those regions previously showing hsp-70 mRNA induction. AMAA-induced hsp-70 mRNA expression was prevented by pre-treatment with the non-competitive NMDA antagonist MK-801. These results suggest that NMDA receptors are involved in the stress response induced by AMAA.

Time course of protein changes following in vitro ischemia in the rat hippocampal slice

Following 5 min in vitro ischemia, total protein synthesis is dramatically and persistently inhibited in neurons in the rat hippocampal slice. This model system was used to explore the responses of individual proteins to this irreversible insult. In vitro ischemia inhibited new protein synthesis of most proteins analyzed; however, the synthesis of a 68/70 kDa protein was substantially stimulated for the first hour after ischemia. By 3 hr postischemia, its synthesis rates were depressed to 60% of control rates. Although the total amounts of most proteins were not significantly depleted for the first few hours after ail ischemic episode, there were several notable exceptions. The levels of HSC73, a constitutively expressed member of the 70 kDa stress protein family, were reduced after in vitro ischemia. In addition, MAP-2 (microtubule-associated protein-2) and alpha-tubulin were depleted in the early hours after the insult, with MAP-2 exhibiting a detectable depletion earlier than tubulin. In contrast, the levels and distribution of a 68 kDa neurofilament protein localized to CA3 pyramidal neurons in the slice, apparently distinct from the band whose new synthesis was stimulated, were not affected by the 5 min in vitro ischemia insult. Thus, the responses of individual proteins to ischemia varied considerably, These individual responses could play an important role in the damage mechanism that is initiated in response to in vitro ischemia.

Survival of parvalbumin-immunoreactive neurons in the gerbil hippocampus following transient forebrain ischemia does not depend on HSP-70 protein induction

HSP-70 was induced in the gerbil following 20 min of forebrain ischemia. The induction, as revealed with immunohistochemistry, is stronger and longer-lasting in CA3 and dentate gyrus than in CA1. Most neurons in this region, except GABAergic interneurons containing the calcium-binding protein parvalbumin, eventually cease to live as a result of delayed cell death. Double-labeling of inducible HSP-70 and parvalbumin has shown that no co-localization occurs in the hippocampus and neocortex of the gerbil in this model of transient forebrain ischemia. These results show that different thresholds of sensitivity and vulnerability exist for different subpopulations of neurons in the ischemic hippocampus, and suggest that HSP-70 protein induction is probably not essential for the survival of particular neuronal subpopulations subjected to transient ischemia.

Kainic acid-induced heat shock protein-70, mRNA and protein expression is inhibited by MK-801 in certain rat brain regions

The regional expression of inducible 72 kDa heat shock protein (HSP-70), HSP-70 mRNA and the neuropathological outcome of their expression were examined in the rat brain following systemic administration of kainic acid (9 mg/kg), and also after pretreatment with the non-competitive N-methyl-D-aspartate antagonist MK-801 (1 mg/kg). Five hours after administration of kainic acid alone, dense expression of HSP-70 mRNA was found within the limbic system, mainly in the hippocampus, piriform and entorhinal cortices, amygdaloid complex, thalamic nuclei, subiculum and in other cortical areas in rats that had shown convulsive behaviour. At 24 h, HSP-70 immunoreactivity was seen in most areas previously expressing HSP-70 mRNA, except the piriform and entorhinal cortices and several ventral nuclei of the amygdaloid complex. Histopathological examination at 24 h revealed marked cell loss in these latter regions and less severe histopathological changes in other areas of the limbic system in brains of convulsive rats. No alterations were apparent in non-convulsive rats. The percentage of rats showing convulsive behaviour with kainic acid was reduced from 74 to 4% following pretreatment with MK-801. In addition, MK-801 inhibited the kainic acid-induced expression of HSP-70 mRNA and protein in certain brain regions, notably the cortex, the pyramidal cell layer of CA1, and discrete thalamic nuclei. However, HSP-70 mRNA induction was sustained in the pyramidal cell layer of CA3, the amygdaloid complex and the subiculum, despite the fact that none of these rats convulsed. MK-801 prevented necrosis in all rats examined except the single rat that had shown convulsive behaviour. These results show that early regional expression of inducible HSP-70 mRNA allows the visualization of regions affected by kainic acid and maps regions inhibited by MK-801. In addition, the results identify brain regions putatively involved in the manifestation of limbic convulsions. Furthermore, these data illustrate that the induction of HSP-70 mRNA is not predictive of cell death or survival.

Expression of c-fos and inducible hsp-70 mRNA following a transient episode of focal ischemia that had non-lethal effects on the rat brain

Expression of c-fos and inducible hsp-70 mRNA was studied with in situ hybridization techniques at different times following an episode of middle cerebral artery (MCA) occlusion not resulting in any apparent lethal effect on the rat brain. hsp-70 and c-fos mRNA were found in the ipsilateral striatum and adjacent cortex. In the striatum, levels of hsp-70 mRNA increased from 1 to 2 and 4 h of reperfusion, whereas levels of c-fos mRNA decreased from 1 to 4 h of reperfusion. These results demonstrate that following non-lethal focal ischemia the brain areas within the MCA territory show high c-fos and hsp-70 mRNA expression response, illustrating the concomitant induction of these mRNAs in cells that survive the ischemic insult.

Regional expression of inducible heat shock protein-70 mRNA in the rat brain following administration of convulsant drugs

Expression of inducible heat shock protein-70 mRNA (hsp-70 mRNA) was studied in the rat brain following systemic administration of different convulsant agents: an L-type voltage-dependent calcium channel agonist, (+/-)-BAY K 8644 (BAY-K); the excitotoxic glutamate agonists kainic acid and N-methyl-D-aspartic acid (NMDA); and the GABAA receptor complex antagonists pentylenetetrazole (PTZ) and lindane (gamma-hexaclorocyclohexane). BAY-K induced minimal hsp-70 mRNA expression in the hippocampus of convulsant rats, localized in the dentate gyrus and the pyramidal cell layer of Ammon's horn. Kainic acid treatment in rats, showing severe limbic convulsions, caused intense expression of hsp-70 mRNA and protein (HSP-70). Expression was localized in select cerebral regions, notably the pyramidal cell layer of the hippocampal CA3 field of Ammon's horn and the piriform cortex, and also the subicular complex and the amygdala, and, to a lesser extent, the entorhinal cortex, the pyramidal cell layer of CA1, several thalamic nuclei, and the parietal cortex. In contrast, systemic administration of NMDA, PTZ or lindane led to no detectable induction of hsp-70 mRNA in the rat brain, despite producing convulsions. Histological examination revealed cell injury only following kainic acid treatment. Damage was most apparent in the piriform and entorhinal cortices, pyramidal cell layer of the CA1 field, and cortical amygdaloid nuclei. BAY-K, NMDA, PTZ and lindane did not lead to any observable histopathological changes. These results show that convulsions of different aetiology do not inevitably induce hsp-70 mRNA expression or cell damage. Intense expression of hsp-70 mRNA was generally associated with regions that later showed variable degrees of nerve cell damage, although hsp-70 mRNA expression was not always predictive of subsequent cell death or survival.

Hemeoxygenase expression after reversible ischemia of rat brain

Heme oxygenase (HO-1) gene expression was studied in the brains of rats subjected to 30 min global cerebral ischemia followed by recirculation of up to 24 h. Total RNA was isolated from the cerebral cortex, striatum and hippocampus and reverse-transcribed into cDNA. cDNA was taken as template for PCR using HO-1-specific primers. We found that, when PCR reactions were run for 22 cycles, the amount of PCR products correlated closely with the amount of cDNA. HO-1 gene expression was sharply increased after cerebral ischemia in all three brain structures studied. In the cortex and striatum, the HO-1 mRNA content increased constantly after cerebral ischemia up to 24 h of recovery, being 8- and 9-fold over control after 24 h of recirculation in the cortex and striatum, respectively. In the hippocampus, HO-1 mRNA levels peaked at 4 h after ischemia (9-fold over control) and declined thereafter to 4.5-fold over control 24 h after ischemia. Assuming that the observed increase in mRNA levels is paralled by increased HO-1 protein synthesis, formation of the products of HO reaction, biliverdin and carbon monoxide, is activated after ischemia. These products may produce different and divergent effects on the recovery from the metabolic stress produced by cerebral ischemia.

Induction of HSP70 mRNA and HSP70 protein in the hippocampus of the developing gerbil following transient forebrain ischemia

The effects of a 20-min transient episode of forebrain ischemia on the induction of HSP70 mRNA and protein, and the histopathological outcome in the hippocampus of the developing gerbil, were examined at postnatal days (P) 7, 15, 21 and 30 and in adulthood. 4 days after the ischemic episode, P7 gerbils did not show apparent histological abnormalities; however, from P15 onwards, ischemia resulted in necrosis in selected areas of the hippocampus. At P15 and P21, necrosis was observed in the base of the granular cell layer of the dentate gyrus and in the CA3 pyramidal cell layer, whereas at P30 and adult necrosis was apparent in the CA1 pyramidal cell layer. HSP70 mRNA induction was not found in ischemic P7 and P15 gerbils while, from P21 onwards, induction was observed in the dentate gyrus and CA1 pyramidal cell layer. In addition, at P30 and adult, HSP70 mRNA expression was also seen in CA3 pyramidal cell layer. Induction of HSP70 immunoreactivity was not seen at P7 but, from P15 onwards, ischemia induced HSP70 immunoreactivity in different areas: in dentate gyrus granular and molecular layers, from P15 onwards; in CA1 pyramidal cell layer, from P21 onwards; and in CA3 pyramidal cell layer, from P30 onwards. Results show selective age-dependent patterns of vulnerability to ischemia in the gerbil hippocampus which, overall, were not well-correlated to the corresponding HSP70 mRNA and protein induction patterns.