Neuronal induction of 72-kDa heat shock protein following methamphetamine-induced hyperthermia in the mouse hippocampus

Drug- and/or trauma-induced hyperthermia? Characterization of HSP70 and myoglobin expression

Introduction

Heat shock protein 70 (HSP70) expression could be discussed as an adaption that promotes repair and counteracts cell damage. Myoglobin is released upon muscle damage of several pathways. The purpose of the present study was to determine whether the expression of HSP70 in kidney, heart and brain and of myoglobin in the kidney were associated with the cause of death and the survival times after lethal intoxications with three of the drugs most widely used in our local area (Saxony, Germany) as well as after fatal traumatic brain injury (TBI).

Methods

We retrospectively collected kidney, heart and brain samples of 50 autopsy cases with toxicological proved lethal intoxication (main drugs methamphetamine, morphine, alcohol), 14 TBI cases and 15 fatalities with acute myocardial injury in age- and gender-matched compilations.

Results

Our main findings suggest that HSP70 is associated with hyperthermal and other stress factors of most cell populations. HSP70 expressions in kidney and heart muscle are useful for a differentiation between fatal intoxications and cases without toxicological influence (p < 0.05). There were significant differences in the cerebral expression patterns between methamphetamine- and morphine-associated deaths compared to alcohol fatalities (p < 0.05). An intensive staining of HSP70 in the pericontusional zone and the hippocampus after TBI (especially neuronal and vascular) was shown even after short survival times and may be useful as an additional marker in questions of vitality or wound age. A relevant myoglobin decoration of renal tubules was only shown for methamphetamine abuse in the study presented.

Conclusion

In sum, the immunohistochemical characteristics presented can be supportive for determining final death circumstances and minimal trauma survival times but are not isolated usefully for the detection of drug- or trauma-induced hyperthermia.

Drug abuse and the neurovascular unit

Drug abuse continues to create a major international epidemic affecting society. A great majority of past drug abuse research has focused mostly on the mechanisms of addiction and the specific effects of substance use disorders on brain circuits and pathways that modulate reward, motivation, craving, and decision making. Few studies have focused on the neurobiology of acute and chronic substance abuse as it relates to the neurovascular unit (brain endothelial cell, neuron, astrocyte, microglia, and pericyte). Increasing research indicates that all cellular components of the neurovascular unit play a pivotal role in both the process of addiction and how drug abuse affects the brain response to diseases. This review will focus on the specific effects of opioids, amphetamines, alcohol, and nicotine on the neurovascular unit and its role in addiction and adaption to brain diseases. Elucidation of the role of the neurovascular unit on the neurobiology associated with drug addiction will help to facilitate the development of better therapeutic approaches for drug-dependent individuals.

Serum myoglobin, but not lipopolysaccharides, is predictive of AMPH-induced striatal neurotoxicity

Determinants of amphetamine (AMPH)-induced neurotoxicity are poorly understood. The role of lipopolysaccharides (LPS) and organ injury in AMPH-induced neurotoxicity was examined in adult male Sprague-Dawley rats that were give AMPH and became hyperthermic during the exposure. Environmentally-induced hyperthermia (EIH) in the rat was compared to AMPH to determine whether AMPH-induced increases in LPS and peripheral toxicities were solely attributable to hyperthermia. Muscle, liver, and kidney function were determined biochemically at 3h or 1 day after AMPH or EIH exposure and histopathology at 1 day after treatment. Circulating levels of LPS were monitored (via limulus amoebocyte coagulation assay) during AMPH or EIH exposure. Blood LPS levels were detected in 40-50% of the AMPH and EIH rats, but the presence of LPS in the serum had no effect on organ damage or striatal dopamine depletions (neurotoxicity). In both CR and NCTR rats, serum bound urea nitrogen and creatinine levels increased at 3h after EIH or AMPH (2- to 3-fold above control) but subsided by 1 day. Alanine transaminase was increased (indicating liver dysfunction) by both AMPH and EIH at 3 h (2- to 10-fold above control) in CR rats, but the levels were not significantly different between the control and AMPH groups in NCTR animals. Mild liver necrosis was detected in 1 of 7 rats examined in the AMPH group and in 1 of 5 rats examined in the EIH group (only NCTR rats were examined). Serum myoglobin increased (indicating muscle damage) in both CR and NCTR rats at 3h and was more pronounced with AMPH (≈5-fold above control) than EIH. Our results indicate that: (1) "free" blood borne LPS often increases with EIH and AMPH but may not be necessary for striatal neurotoxicity and CNS immune responses; (2) liver or kidney dysfunction may result from muscle damage; however, it is not sufficient nor necessary to produce, but may exacerbate, neurotoxicity; (3) AMPH-induced serum myoglobin release is a potential biomarker and possibly a factor in AMPH-induced toxicity processes.

Markers associated with testosterone enhancement of methamphetamine-induced striatal dopaminergic neurotoxicity

Intact male CD-1 mice received an injection of testosterone propionate (TP--5 ug), progesterone (P--5 mg), the oil vehicle or remained untreated (control). At 24 hours after hormonal treatments the mice received an injection of methamphetamine (MA--40 mg/kg) and rectal temperatures were measured. At 5 days post-MA, assays were performed to assess effects of these treatments. Maximal increases in body temperatures, that were significantly greater than oil-treated controls, were obtained in TP-treated mice. At 5 days post-MA, maximal weight reductions were obtained with TP-treated mice, while P-treated mice showed no significant decrease between the pre- versus post-MA determinations. Striatal dopamine concentrations showed maximal reductions and heat-shock protein-70 maximal increases in the TP group, with both differing significantly as compared with all other groups. Protein levels of dopamine transporters were significantly decreased in P-treated mice, while vesicular monoamine transporter-2 was significantly decreased in TP-treated mice. Taken together, these results suggest that testosterone exacerbates the deleterious effects of MA within male mice as indicated by a number of markers related to neurotoxicity. The changes in markers as associated with this enhanced neurotoxicity suggest that TP may increase thermal/energy responses and/or oxidative stress to produce this effect.

Involvement of dopamine receptors in binge methamphetamine-induced activation of endoplasmic reticulum and mitochondrial stress pathways

Single large doses of methamphetamine (METH) cause endoplasmic reticulum (ER) stress and mitochondrial dysfunctions in rodent striata. The dopamine D₁ receptor appears to be involved in these METH-mediated stresses. The purpose of this study was to investigate if dopamine D₁ and D₂ receptors are involved in ER and mitochondrial stresses caused by single-day METH binges in the rat striatum. Male Sprague-Dawley rats received 4 injections of 10 mg/kg of METH alone or in combination with a putative D₁ or D₂ receptor antagonist, SCH23390 or raclopride, respectively, given 30 min prior to each METH injection. Rats were euthanized at various timepoints afterwards. Striatal tissues were used in quantitative RT-PCR and western blot analyses. We found that binge METH injections caused increased expression of the pro-survival genes, BiP/GRP-78 and P58^IPK, in a SCH23390-sensitive manner. METH also caused up-regulation of ER-stress genes, Atf2, Atf3, Atf4, CHOP/Gadd153 and Gadd34. The expression of heat shock proteins (HSPs) was increased after METH injections. SCH23390 completely blocked induction in all analyzed ER stress-related proteins that included ATF3, ATF4, CHOP/Gadd153, HSPs and caspase-12. The dopamine D₂-like antagonist, raclopride, exerted small to moderate inhibitory influence on some METH-induced changes in ER stress proteins. Importantly, METH caused decreases in the mitochondrial anti-apoptotic protein, Bcl-2, but increases in the pro-apoptotic proteins, Bax, Bad and cytochrome c, in a SCH23390-sensitive fashion. In contrast, raclopride provided only small inhibition of METH-induced changes in mitochondrial proteins. These findings indicate that METH-induced activation of striatal ER and mitochondrial stress pathways might be more related to activation of SCH23390-sensitive receptors.

Expression of heat shock protein (HSP 72 kDa) during acute methamphetamine intoxication depends on brain hyperthermia: neurotoxicity or neuroprotection?

In the present study, light and electron microscopy were used to examine heat shock protein (HSP 72 kD) expression during acute methamphetamine (METH) intoxication in rats and evaluate its relationships with brain temperature and alterations in a number of other histochemical and morphological parameters. Freely moving rats received METH at the same dose (9 mg/kg, sc) but at different ambient temperatures (23 and 29°C), showing a wide range of brain temperature elevations (37.6-42.5°C); brains were taken for histochemical and morphological evaluations at peak of brain temperature increase. We found that acute METH intoxication induces massive and wide-spread HSP expression in neural and glial cells examined in detail in the cortex, hippocampus, thalamus, and hypothalamus. In each of these structures, the number of HSP-positive cells tightly correlated with brain temperature elevation. The changes in HSP immunoreactivity were also tightly related to alterations in permeability of the blood-brain barrier, acute glial activation, and brain edema assessed by albumin and GFAP immunoreactivity and measuring tissue water content, respectively. While robust and generalized HSP production normally appears to be the part of an adaptive brain response associated with METH-induced metabolic activation, activation of this protective mechanism has its natural limits and could not counteract the damaging effects of oxidative stress, high temperature, and edema--the leading factors of METH-induced neurotoxicity.

Detection of methamphetamine neurotoxicity in forensic autopsy cases

Methamphetamine (METH) is a powerful stimulant drug of abuse with potent addictive and neurotoxic properties. METH neurotoxicity is characterized by the long-term depletion of striatal monoamines. METH-induced release of dopamine generates reactive hydrogen species, which are proposed to play an important role in METH neurotoxicity. The tyrosine hydroxylase (TH), dopamine transporter (DAT), and vesicular monoamine transporter 2 (VMAT2) levels and glial reactions in the striata of METH abusers were examined using immunohistochemical technique. Decreases in TH immunoreactivity and DAT levels were evident in METH users. Although significant differences in VMAT2 levels were not common, the levels of VMAT2--a stable marker of striatal dopaminergic terminal integrity--were remarkably reduced in some METH users. Further, significant increases were observed in the number of microglia in the striatum although the activation of glial cells was not evident. In addition, the expression of 72-kDa heat shock proteins (HSP72) in the brains of METH abusers was assessed. HSP72 immunoreactivity was observed in the hippocampus and other areas. These findings may be indicative of hyperthermia due to METH-induced neurotoxicity although it is possible that HSPs are induced by other effects of METH. Immunohistochemical detection of dopaminergic terminal marker deficits, glial reactions, and HSP induction might provide useful information regarding the pathophysiology of chronic and/or lethal METH use in cases of METH-related deaths, where METH intoxication may not be toxicologically demonstrated.

Selective Changes in Gene Expression in Cortical Regions Sensitive to Amphetamine During the Neurodegenerative Process

Gene expression profiles in several brain regions of adult male rats were evaluated following a d-amphetamine (AMPH) exposure paradigm previously established to produce AMPH neurotoxicity. Escalating doses of AMPH (5-30 mg/kg) were given over the course of 16 h per day in an 18 degrees C environment for 2 days. This paradigm produces neurotoxicity but eliminates or minimizes the hyperthermia and seizure activity that might influence gene expression in a manner unrelated to the neurotoxic effects of AMPH. The expression of 1185 genes was monitored in the striatum, parietal cortex, piriform cortex and posteriolateral cortical amygdaloid nucleus (PLCo) using cDNA array technology, and potentially significant changes were verified by RT-PCR. Gene expression was determined at time points after AMPH when neurodegeneration was beginning to appear (16 h) or maximal (64 h). Expression was also determined 14 days after AMPH to find long-term changes in gene expression that might be biomarkers of a neurotoxic event. In the parietal cortex there was a two-fold increase in neuropeptide Y precursor protein mRNA whereas nerve growth factor-induced receptor protein I-A and I-B mRNA decreased 50% at 16 h after the end of AMPH exposure. Although these changes in expression were not observed in the PLCo, insulin-like growth factor binding protein 1 mRNA was increased two-fold in the PLCo at 16 and 64 h after AMPH. Changes in gene expression in the cortical regions were all between 1.2- and 1.5-fold 14 days after AMPH but some of these changes, such as annexin V increases, may be relevant to neurotoxicity. Gene expression was not affected by more than 1.5-fold at the time points in the striatum, although 65% dopamine depletions occurred, but the plasma membrane-associated dopamine transporter and dopamine D2 receptor were decreased about 40% in the substantia nigra at 64 h and 14 days post-AMPH. Thus, the 2-day AMPH treatment produced a few changes in gene expression in the two-fold range at time points 16 h or more after exposure but the majority of expression changes were less than 1.5-fold of control. Nonetheless, some of these lesser fold-changes appeared to be relevant to the neurotoxic process.

Hyperthermic induction of the 27-kDa heat shock protein (Hsp27) in neuroglia and neurons of the rat central nervous system

The 27-kDa heat shock protein (Hsp27) is constitutively expressed in many neurons of the brainstem and spinal cord, is strongly induced in glial cells in response to ischemia, seizures, or spreading depression, and is selectively induced in neurons after axotomy. Here, the expression of Hsp27 was examined in brains of adult rats from 1.5 hours to 6 days after brief hyperthermic stress (core body temperature of 42 degrees C for 15 minutes). Twenty-four hours following hyperthermia, Western blot analysis showed that Hsp27 was elevated in the cerebral cortex, hippocampus, cerebellum, and brainstem. Immunohistochemistry for Hsp27 revealed a time-dependent, but transient, increase in the level of Hsp27 immunoreactivity (Hsp27 IR) in neuroglia and neurons. Hsp27 IR was detected in astrocytes throughout the brain and in Bergmann glia of the cerebellum from 3 hours to 6 days following heat shock. Peak levels were apparent at 24 hours, gradually declining thereafter. In addition, increases in Hsp27 IR were detected in the ependyma and choroid plexus. Hyperthermia induced Hsp27 IR in neurons of the subfornical organ and the area postrema within 3 hours and reached a maximum by 24 hours with a return to control levels 4-6 days after hyperthermia. Specific populations of hypothalamic neurons also showed Hsp27 IR after hyperthermia. These results demonstrate that hyperthermia induces transient expression of Hsp27 in several types of neuroglia and specific populations of neurons. The pattern of induced Hsp27 IR suggests that some of the activated cells are involved in physiological responses related to body fluid homeostasis and temperature regulation.

Two inbred strains of rats, Fischer 344 and Lewis, showed differential behavior and brain expression of corticosterone receptor mRNA induced by methamphetamine

Recently, a role of the hypothalamo-pituitary-adrenocortical (HPA) axis in facilitating the behavioral and neurochemical effects of psychostimulants has been proposed. Two inbred strains of rats, Fischer 344/N (F344) and Lewis/N (LEW), have markedly different HPA axes as well as behavioral responses to psychostimulants: F344 rats show hyperresponsive HPA axis and no significant sensitization to cocaine, whereas LEW rats display blunted response in HPA axis and develop cocaine-induced locomotor sensitization. Corticosterone exerts its biological effects via intracellular receptors, termed type I (mineralocorticoid receptor: MR) and type II (glucocorticoid receptor: GR). The present study examines the development of stereotypy sensitization and the brain expression of mRNAs for MR, GR, and heat shock protein 90 (HSP90) in methamphetamine (MAP)-treated F344 and LEW rats. Animals received i.p. injections with chronic saline (SAL: once daily for 21 days), chronic saline and acute MAP (AM: saline for 20 days and 4 mg/kg MAP on the 21st day), or chronic MAP (CM: 4 mg/kg MAP for 21 days) and were sacrificed three hours after the last injections. Striatum, hippocampus, and cerebellum were quickly dissected on ice and total RNA was isolated for northern analyses. LEW rats developed stereotypy sensitization significantly earlier than F344 rats. AM significantly decreased GR and MR mRNA expression in hippocampus of LEW, compared to SAL. CM significantly increased GR and MR mRNA expression in striatum of F344 compared to SAL and AM, while it decreased GR mRNA in striatum of LEW and MR mRNA in hippocampus, compared to SAL. AM significantly increased HSP90 mRNA in all brain regions examined, without the hippocampus in LEW. CM significantly increased the expression of HSP90 mRNA in the striatum and cerebellum of F344, but significantly decreased in the striatum and hippocampus of LEW. These contrasting differences between F344 and LEW, in their susceptibility to stereotypy sensitization and striatal expression of GR mRNA by chronic MAP, suggest that some striatal genes, whose transcription is regulated by GR, play a crucial role in the development of MAP-induced behavioral sensitization.

Changes in mRNA levels for heat-shock/stress proteins (Hsp) and a secretory vesicle associated cysteine-string protein (Csp1) after amphetamine (AMPH) exposure

Damage to nerve terminals, reactive gliosis and somatic degeneration can result when pronounced hyperthermia occurs during amphetamine (AMPH) exposure. The effects of AMPH-induced hyperthermia and damage on the relative mRNA levels for several heat shock/stress proteins (Hsp27, Hsp60, Hsp70 and Hsc70), as well as secretory vesicle associated cysteinestring protein (Csp1) were determined in both the striatum and substantia nigra using reverse transcriptase polymerase chain reaction (RT-PCR). These changes were compared to changes in Hsp mRNA levels seen in primary rat cerebral astrocyte cultures after heat shock/stress. Striatal Hsp70 mRNA increased about 2-fold over control levels at 16 hr after AMPH-induced hyperthermia, and was the only Hsp species to significantly increase in response to AMPH. Hsp70 mRNA levels returned to control within 14 days after AMPH. Two-fold increases in Hsp70 mRNA were also seen in primary cultures of rat cerebrum 24 hr after heat shock. In primary cultures and brain tissue, the increased Hsp70 mRNA levels were still more than 500-fold less than constitutive Hsc70 mRNA and 50-fold less than Hsp60 levels. Hsp27 mRNA was not present in the striatum, nigra and primary cell cultures. Thus, the expression of Hsp species mRNA measured was very similar in brain tissue and primary cell cultures. Because only a modest induction of Hsp 70 mRNA occurred, the Hsp species evaluated may only play a minor role in AMPH neurotoxicity. However, further studies are necessary to determine whether large increases in Hsp70 are occurring in selected neurons or glia in the striatum. RT-PCR products for Csp1 were produced in total RNA obtained from brain but not from cultured astrocytes, suggesting that the Csp1 mRNA measured by RT-PCR is of neuronal origin. Csp1 mRNA levels were acutely downregulated in neurons in the substantia nigra, possibly in response to damage, but not the striatum after AMPH exposure. A slight long-term upregulation at 4 months of Csp1 mRNA may occur in the striatum but not in nigra.

Cell specific expression of Hsp70 in neurons and glia of the rat hippocampus after hyperthermia and kainic acid-induced seizure activity

In this study we investigated the time course, cell-type and stress-specific expression of hsp70 mRNA and Hsp70 protein in glial cells and neurons in the rat brain following heat shock treatment and kainic acid-induced status epilepticus. Transcripts for hsp70 were detected in hippocampal homogenates from 1.5 to 6 h following hyperthermia and from 3 to 24 h following kainic acid-induced seizures. In situ hybridization revealed hsp70 mRNA to be region specific and time-dependent following hyperthermia and kainic acid-induced seizures. Western analysis indicated that Hsp70 reached maximal levels at 3 h after hyperthermia and 12 h after kainic acid-induced seizures. Immunohistochemistry revealed low level expression of Hsp70 protein in dentate granule cells at 1.5 and 3 h after hyperthermia. No Hsp70 protein was detected in neurons of the pyramidal cell layer or dentate hilus at any time following hyperthermia. Small Hsp70-immunoreactive cells were detected throughout the hippocampus following hyperthermia that, based on cell size, distribution, and double-labeling with vimentin, were considered to be glia. In contrast, high levels of Hsp70 protein were detected in neurons of the pyramidal cell layer and dentate hilus at 24 h after seizure-inducing kainic acid injection. These results suggest that expression of Hsp70 protein is cell-specific depending on the stressor. In addition, finding high levels of Hsp70 mRNA in the dentate granule cells after hyperthermia, but little or no Hsp70 protein, suggests that the synthesis of the protein is also regulated at the post-transcriptional level following hyperthermia.

Ibogaine blocked methamphetamine-induced hyperthermia and induction of heat shock protein in mice

Body temperature changes and heat shock protein (HSP-72) induction in the caudate nucleus were studied in female C57BL/6N mice pretreated with ibogaine (50 mg/kg) and sacrificed 48 h. after a single dose of methamphetamine (20 mg/kg). Methamphetamine injection resulted in hyperthermia and induced HSP-72 expression, whereas treatment with ibogaine alone produced hypothermia. The ibogaine followed by methamphetamine injection showed no hyperthermia and decreased HSP-72 expression. These data indicate that pretreatment with ibogaine can completely block methamphetamine-induced hyperthermia and HSP-72 expression in the striatum.

Methamphetamine-induced hyperthermia in mice: examination of dopamine depletion and heat-shock protein induction

Methamphetamine (METH) is a common drug of abuse and a clinical anoretic which is known to cause neurotoxicity in rodents as evidenced by a depletion of dopamine (DA) and by decreased numbers of DA uptake sites in the striatum. It is also known to cause hyperthermia which is believed to induce the production of the 72-kDa heat-shock protein (HSP-72). In the present study, we evaluated whether METH induced the production of HSP-72 in both the mouse hippocampus and striatum and also attempted to correlate this induction with monoamine depletion. Adult male C57BL/6N mice received METH (20 mg/kg, i.p.) in an ambient temperature of 27 degrees C and body temperatures were monitored up to 240 min after treatment. Animals were sacrificed 12, 18, 24, 39, and 48 h after treatment. One striatum was examined for DA, DOPAC, and HVA levels using HPLC-EC and the contralateral striatum, along with the hippocampus, was prepared for immunoblotting. HPLC-EC analysis revealed a significant depletion of DA, DOPAC, and HVA at all time points. There was, however, a significant increase in DA at 48 vs. 39 h. A biphasic production of HSP-72, in both the hippocampus and striatum, was detected by immunoblot. HSP-72 production was strong at 12 h which corresponds to neuronal induction. However, at 18 h in the striatum and 24 h in the hippocampus, the induction appears to be reduced. A second phase of HSP-72 induction occurred at 39 h in both regions. In a second experiment, mice were dosed according to the same paradigm and were perfused at 18 h after treatment for immunohistochemical analysis. HSP-72 immunoreactivity was found in neurons of the CA1 and CA4 regions of the hippocampus; however, no detectable response was evident in the striatum. In conclusion, these data demonstrate that a single injection of METH can lead to hyperthermia which may then result in both the induction of HSP-72 and depletion of DA concentration.

Gradation of kainic acid-induced rat limbic seizures and expression of hippocampal heat shock protein-70

Systemic injection of kainic acid (KA) induces limbic seizures in rats, which resemble human temporal lobe epilepsy, the most common form of adult human epilepsy. In this study, we have investigated KA-elicited limbic seizures in the rats by correlating the severity of the seizure attacks with the expression of hippocampal heat shock protein-70 (HSP70) which has been suggested to be a marker for neuronal injury/death in this model of seizures. After a systemic injection of KA, six stages of limbic seizures have been classified, namely, staring (stage 1), wet dog shake (stage 2), hyperactivity (stage 3), rearing (stage 4), rearing and falling (stage 5), and jumping (stage 6). Stages 4, 5 and 6 were further divided into mild and severe sub-stages. HSP70 expression was not detected in animals with stages 1 and 2 seizures. At stage 3 a small amount of HSP70 immunoreactive neurons was detected in the CA3 field and the dentate hilus. From stage 4 to stage 5 the degree of HSP70 immunoreactivity increased in the CA1 field from a few positive cells in stage 4 mild to large numbers of immunoreactive neurons in stage 5 severe. HSP70 became detectable in pyramidal cells in the CA2 field from stage 5 severe and higher. In animals with stage 6 seizures, the majority of HSP70 expression became located in glial cells throughout the whole hippocampus. We concluded that HSP70 expression in the hippocampus positively correlates with the severity of KA-elicited limbic seizures.

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.

The effects of reduced perfusion and reperfusion on c-fos and HSP-72 protein immunohistochemistry in gestational day 21 rat brains

Metabolic stressors such as hyperthermia, seizures and ischemic hypoxia result in the induction of c-fos and heat-shock proteins (HSP) in affected brain cells of the adult rodent, especially within the hippocampal region, which normally has high metabolic demands. Here we ligated the uterine vessels of gestational day (GD) 21 rat pups to produce ischemic hypoxia. We confirmed that HSP-72 protein, as previously reported, was activated in the perinatal rat pup, especially in the hippocampal CA3 region. However, the capability of hippocampal cells to produce c-fos protein following drug-induced seizures has been reported to develop only after postnatal day 13. Here, ischemic hypoxia caused CA1 hippocampal cells to produce immunohistochemically detectable c-fos protein in GD-21 rats. These results seem to contradict the previous reports of no c-fos induction in rats this young by demonstrating a functional c-fos translational mechanism by GD-21. However, seizure vs ischemic hypoxia-induced c-fos expression may involve several different pre-translational pathways. A delayed development of a receptor, second messenger, or genomic element for regulating c-fos transcription remain as possible explanations for the late maturity of responsivity to seizures.

Occurrence of heat shock response in deafferented neurons in the substantia nigra of rats

The substantia nigra is innervated by massive inhibitory GABAergic projections from the striatum and globus pallidus, deafferentation of which is supposed to lead to anterograde trans-synaptic degeneration of the nigral neurons. An immunohistochemical method was used to examine the induction of 72,000 mol. wt heat shock protein in the substantia nigra following cerebral hemitransection or transient middle cerebral artery occlusion. At three and four days post-transection, strong immunoreactivity for 72,000 mol. wt heat shock protein was found in the ipsilateral substantia nigra pars reticulata. Light microscopic observation revealed a number of pars reticulata neurons showing strong immunoreactivity for 72,000 mol. wt heat shock protein in their perikarya and proximal processes. In addition, Golgi-like stained neurons with dystrophic features were occasionally observed in the ipsilateral substantia nigra pars reticulata. The immunoreactivity for 72,000 mol. wt heat shock protein in the ipsilateral pars reticulata gradually declined and almost disappeared by 15 days after transection. No apparent induction of 72,000 mol. wt heat shock protein was found in the substantia nigra pars compacta throughout the time period examined. Massive striatal ischemic injury produced by transient middle cerebral artery occlusion also induced expression of 72,000 mol. wt heat shock protein in the pars reticulata neurons three and four days postoperatively. These findings suggest that deafferentation of the striatal or striatopallidal inputs per se is a harmful stress for the substantia nigra pars reticulata neurons, inducing 72,000 mol. wt heat shock protein synthesis. The present data may contribute to our understanding of the molecular basis of the pathomechanism of the transneuronal regression of substantia nigra pars reticulata neurons, which may occur after removal of inhibitory GABAergic inputs.