Cortical application of potassium chloride induces the low-molecular weight heat shock protein (Hsp27) in astrocytes

The effect of female sex hormones on Hsp27 phosphorylation and histological changes in prefrontal cortex after tMCAO

BACKGROUND

Female sex hormones are protective factors against many neurological disorders such as brain ischemia. Heat shock protein like HSP27 is activated after tissue injury. The main purpose of the present study is to determine the effect of a combined estrogen / progesterone cocktail on the morphology of astrocytes, neurons and Hsp27 phosphorylation after cerebral ischemia.

METHODS

One hour after the MCAO induction, a single dose of estrogen and progesterone was injected. The infarct volume was calculated by TTC staining 24 h after ischemia. Immunohistochemistry was used to show the effects of estrogen and progesterone on astrocyte and neuron morphology, as well as the Western blot technique used for the quantitation of phosphorylated Hsp27.

RESULTS

The combined dose of estrogen and progesterone significantly decreased astrocytosis after ischemia and increased neuron survival. There was a large increase in Hsp27 phosphorylation in the penumbra ischemic region after stroke, which was significantly reduced by hormone therapy.

CONCLUSION

Our results indicate that the neuroprotective effect of neurosteroids in the brain may be due to the modulation of heat shock proteins.

KCl-induced cortical spreading depression waves more heterogeneously propagate than optogenetically-induced waves in lissencephalic brain: an analysis with optical flow tools

Although cortical spreading depolarizations (CSD) were originally assumed to be homogeneously and concentrically propagating waves, evidence obtained first in gyrencephalic brains and later in lissencephalic brains suggested a rather non-uniform propagation, shaped heterogeneously by factors like cortical region differences, vascular anatomy, wave recurrences and refractory periods. Understanding this heterogeneity is important to better evaluate the experimental models on the mechanistics of CSD and to make appropriate clinical estimations on neurological disorders like migraine, stroke, and traumatic brain injury. This study demonstrates the application of optical flow analysis tools for systematic and objective evaluation of spatiotemporal CSD propagation patterns in anesthetized mice and compares the propagation profile in different CSD induction models. Our findings confirm the asymmetric angular CSD propagation in lissencephalic brains and suggest a strong dependency on induction-method, such that continuous potassium chloride application leads to significantly higher angular propagation variability compared to optogenetically-induced CSDs.

The role of Toll-like receptor signaling pathways in cerebrovascular disorders: the impact of spreading depolarization

Cerebral vascular diseases (CVDs) are a group of disorders that affect the blood supply to the brain and lead to the reduction of oxygen and glucose supply to the neurons and the supporting cells. Spreading depolarization (SD), a propagating wave of neuroglial depolarization, occurs in different CVDs. A growing amount of evidence suggests that the inflammatory responses following hypoxic-ischemic insults and after SD plays a double-edged role in brain tissue injury and clinical outcome; a beneficial effect in the acute phase and a destructive role in the late phase. Toll-like receptors (TLRs) play a crucial role in the activation of inflammatory cascades and subsequent neuroprotective or harmful effects after CVDs and SD. Here, we review current data regarding the pathophysiological role of TLR signaling pathways in different CVDs and discuss the role of SD in the potentiation of the inflammatory cascade in CVDs through the modulation of TLRs.

The impact of hypoxic-ischemic brain injury on stem cell mobilization, migration, adhesion, and proliferation

Neonatal hypoxic-ischemic encephalopathy continues to be a significant cause of death or neurodevelopmental delays despite standard use of therapeutic hypothermia. The use of stem cell transplantation has recently emerged as a promising supplemental therapy to further improve the outcomes of infants with hypoxic-ischemic encephalopathy. After the injury, the brain releases several chemical mediators, many of which communicate directly with stem cells to encourage mobilization, migration, cell adhesion and differentiation. This manuscript reviews the biomarkers that are released from the injured brain and their interactions with stem cells, providing insight regarding how their upregulation could improve stem cell therapy by maximizing cell delivery to the injured tissue.

Recording, analysis, and interpretation of spreading depolarizations in neurointensive care: Review and recommendations of the COSBID research group

Spreading depolarizations (SD) are waves of abrupt, near-complete breakdown of neuronal transmembrane ion gradients, are the largest possible pathophysiologic disruption of viable cerebral gray matter, and are a crucial mechanism of lesion development. Spreading depolarizations are increasingly recorded during multimodal neuromonitoring in neurocritical care as a causal biomarker providing a diagnostic summary measure of metabolic failure and excitotoxic injury. Focal ischemia causes spreading depolarization within minutes. Further spreading depolarizations arise for hours to days due to energy supply-demand mismatch in viable tissue. Spreading depolarizations exacerbate neuronal injury through prolonged ionic breakdown and spreading depolarization-related hypoperfusion (spreading ischemia). Local duration of the depolarization indicates local tissue energy status and risk of injury. Regional electrocorticographic monitoring affords even remote detection of injury because spreading depolarizations propagate widely from ischemic or metabolically stressed zones; characteristic patterns, including temporal clusters of spreading depolarizations and persistent depression of spontaneous cortical activity, can be recognized and quantified. Here, we describe the experimental basis for interpreting these patterns and illustrate their translation to human disease. We further provide consensus recommendations for electrocorticographic methods to record, classify, and score spreading depolarizations and associated spreading depressions. These methods offer distinct advantages over other neuromonitoring modalities and allow for future refinement through less invasive and more automated approaches.

Cortical spreading depression produces a neuroprotective effect activating mitochondrial uncoupling protein-5

Depression of electrocorticogram propagating over the cortex surface results in cortical spreading depression (CSD), which is probably related to the pathophysiology of stroke, epilepsy, and migraine. However, preconditioning with CSD produces neuroprotection to subsequent ischemic episodes. Such effects require the expression or activation of several genes, including neuroprotective ones. Recently, it has been demonstrated that the expression of the uncoupling proteins (UCPs) 2 and 5 is amplified during brain ischemia and their expression exerts a long-term effect upon neuron protection. To evaluate the neuroprotective consequence of CSD, the expression of UCP-5 in the brain cortex was measured following CSD induction. CSD was evoked in four samples of rats, which were sacrificed after 2 hours, 4 hours, 6 hours, and 24 hours. Western blot analyses were carried out to measure UCP-5 concentrations in the prefrontal cortices of both hemispheres, and immunohistochemistry was performed to determine the localization of UCP-5 in the brain cortex. The results showed a significant elevation in UCP-5 expression at 24 hours in all cortical strata. Moreover, UCP-5 was triggered by CSD, indicating that UCP-5 production can have a neuroprotective effect.

Cortical spreading depression-induced preconditioning in the brain

Cortical spreading depression is a technique used to depolarize neurons. During focal or global ischemia, cortical spreading depression-induced preconditioning can enhance tolerance of further injury. However, the underlying mechanism for this phenomenon remains relatively unclear. To date, numerous issues exist regarding the experimental model used to precondition the brain with cortical spreading depression, such as the administration route, concentration of potassium chloride, induction time, duration of the protection provided by the treatment, the regional distribution of the protective effect, and the types of neurons responsible for the greater tolerance. In this review, we focus on the mechanisms underlying cortical spreading depression-induced tolerance in the brain, considering excitatory neurotransmission and metabolism, nitric oxide, genomic reprogramming, inflammation, neurotropic factors, and cellular stress response. Specifically, we clarify the procedures and detailed information regarding cortical spreading depression-induced preconditioning and build a foundation for more comprehensive investigations in the field of neural regeneration and clinical application in the future.

Neuroprotective effects of compound FLZ in an ischemic model mediated by improving cerebral blood flow and enhancing Hsp27 expression

Compound FLZ is a synthetic novel derivate of natural squamosamide, which has potent neuroprotective effects based on our previous study. We are now aiming to investigate the effects of FLZ on cerebral blood flow (CBF), infarct volume, neurological function, heat shock protein 70 (Hsp70), and Hsp27 expression in transient focal ischemia. For this goal, an animal model of middle cerebral artery occlusion (MCAO) for 2h followed by reperfusion was used, and animals received low or high doses of FLZ (150 or 300mg/kg), orally 10min after MCAO onset. The results show that the infarct volume was 32.7% for the vehicle control group, and reduced to 17.6 and 12.8% for the low and high dose FLZ-treated groups, respectively. FLZ treatment also significantly improved the neurobehavioral score from 2.6 in the vehicle control group to 1.0 and 0.9 in the low and high dose groups, respectively. Further, FLZ significantly induced Hsp27 over-expression and reduced over-expression of HSP70, a sensitive marker of acute ischemia, in ipsilateral cortex by a dose-dependent manner. In addition, CBF was quantified using laser-Doppler flowmetry. During ischemia, regional CBF (rCBF) was improved from approximately 30% to over 50% of the baseline and the reperfusion-induced hyperemia was reduced in both FLZ dosage groups. Particularly, high dose FLZ reduced rCBF during hyperemia by 30%. In conclusion, FLZ (150 and 300mg/kg) can significantly reduce the infarct volume and improve neurobehavioral deficits in a rat MCAO model, most likely through improving CBF in the penumbra and enhancing Hsp27 expression.

Exploiting the diversity of the heat-shock protein family for primary and secondary tauopathy therapeutics

The heat shock protein (Hsp) family is an evolutionarily conserved system that is charged with preventing unfolded or misfolded proteins in the cell from aggregating. In Alzheimer’s disease, extracellular accumulation of the amyloid β peptide (Aβ) and intracellular aggregation of the microtubule associated protein tau may result from mechanisms involving chaperone proteins like the Hsps. Due to the ability of Hsps to regulate aberrantly accumulating proteins like Aβ and tau, therapeutic strategies are emerging that target this family of chaperones to modulate their pathobiology. This article focuses on the use of Hsp-based therapeutics for treating primary and secondary tauopathies like Alzheimer’s disease. It will particularly focus on the pharmacological targeting of the Hsp70/90 system and the value of manipulating Hsp27 for treating Alzheimer’s disease.

Cortical spreading depression differentially affects lysine methylation of H3 histone at neuroprotective genes and retrotransposon sequences

Recently cortical spreading depression (CSD) has been hypothesized to involve epigenetic control of gene expression, by inducing an overall decrease of H3K4 and increase of H3K9 di-methylation. Here we evaluated the H3K4 and H3K9 di-methylation level at specific loci in rat brains 24 h after CSD induction. Analysis of two selected neuroprotective genes, iNOS and HIF-1α, showed marked increase in lysine 4 di-methylation and decrease in lysine 9 di-methylation of H3 histone. In addition, di-methylation of H3K4 increased moving toward 5' end of the genes in CSD-induced rat hemispheres. Such behavior may reflect an epigenetic molecular memory of actively transcribed genes. We extended our analysis on the H3K4 and H3K9 di-methylation levels of two long interspersed sequences (LINEs). We showed that CSD induction led to di-methylation decrease in lysine 4 and increase in lysine 9 of H3 histone, a trend which reflected the overall chromatin changes previously demonstrated. In conclusion, our data corroborate the hypothesis that epigenetic regulation of gene expression can be affected by CSD and that might be a pivotal molecular mechanism of CSD-induced preconditioning phenomenon which induces tolerance to a subsequent episode of ischemia. In such control, we evidenced two effects: i) a molecular memory of transcribed neuroprotective genes, ii) an epigenetic silencing of retrotransposable sequences.

Hyperthermia protects mice against chronic unpredictable stress-induced anxiety-like behaviour and hippocampal CA3 cell apoptosis

PURPOSE

It is widely accepted that chronic stress can induce anxiety; however, the cellular and molecular mechanisms of stress-induced anxiety are far from being elucidated. Hyperthermia has been shown to induce expression of heat shock proteins (HSPs) to provide protection against a variety of stresses. To our knowledge, the effect of hyperthermia on the development of chronic unpredictable stress (CUS)-induced anxiety has not been studied. This study was to determine the relationship between hyperthermia induced Hsp72 and CUS related anxiety.

MATERIALS AND METHODS

Heat shock factor 1 knockout (hsf1(-/-)) and wild-type (hsf1(+/+)) mice were subjected to CUS with or without hyperthermia treatment. Anxiety-like behaviours were evaluated by elevated plus maze and open field tests. Apoptosis in the hippocampal CA3 area was detected by TUNEL staining. Hsp72 protein level in the hippocampus was measured by Western blot.

RESULTS

CUS caused significant apoptosis in hippocampal CA3 cells in both hsf1(-/-) and hsf1(+/+) mice, which significantly correlated with anxiety-like behaviours. Hyperthermia induced Hsp72 expression in hsf1(+/+) mice, but not in hsf1(-/-) mice. Importantly, hyperthermia protected hsf1(+/+) mice against developing CUS-related anxiety-like behaviours and reduced CUS-induced apoptosis in hippocampal CA3 cells. In contrast, hyperthermia exhibited no protective role in hsf1(-/-) mice.

CONCLUSIONS

Apoptosis of hippocampal CA3 cells is involved in the development of anxiety-like behaviours underlying CUS. Hsp72 protein is a crucial player in the protective effect of hyperthermia against CUS-induced apoptosis and development of anxiety-like behaviours. Our study suggests hyperthermia is an effective treatment for CUS-induced mood disorders.

Low ambient temperature reveals distinct mechanisms for MDMA-induced serotonergic toxicity and astroglial Hsp27 heat shock response in rat brain

3,4-Methylenedioxymethamphetamine (MDMA, 'ecstasy') is a widely used recreational drug known to cause selective long-term serotonergic damage. In our recent paper we described region-specific, dose-dependent increase in the protein expression of astroglial Hsp27 and neuronal Hsp72 molecular chaperones after MDMA administration of rats. Here, we examined the possible interaction of elevated Hsp27 protein level to hyperthermic responses after MDMA administration and its separation from drug-induced serotonergic neurotoxicity. For this, 7-8 week old male Dark Agouti rats were treated with 15 mg/kg i.p. MDMA. Treatment at an ambient temperature of 22 ± 1°C caused a significant elevation of the rectal temperature, an increase of Hsp27 immunoreactive protoplasmic astrocytes in the hippocampus, the parietal and cingulate cortices, and a significant decrease in the density of tryptophan hydroxylase immunoreactive fibers in the same brain regions, 8h as well as 24h after drug administrations. In addition, serotonergic axons exhibited numerous swollen varicosities and fragmented morphology. MDMA treatment at low ambient temperature (10 ± 2°C) almost completely abolished the elevation of body temperature and the increased astroglial Hsp27 expression but failed to alter - or just slightly attenuated - the depletion in the density of tryptophan hydroxylase immunoreactive fibers. These results suggest that the increased astroglial Hsp27 protein expression is rather related to the hyperthermic response after the drug administration and it could be separated from the serotonergic neurotoxicity caused by MDMA. In addition, the induction of Hsp27 per se is uneffective to protect serotonergic fibers after MDMA administration. Our results also suggest that Tph immunohistochemistry is an early and sensitive method to demonstrate MDMA-caused vulnerability.

Identification of ischemic regions in a rat model of stroke

BACKGROUND

Investigations following stroke first of all require information about the spatio-temporal dimension of the ischemic core as well as of perilesional and remote affected tissue. Here we systematically evaluated regions differently impaired by focal ischemia.

METHODOLOGY/PRINCIPAL FINDINGS

Wistar rats underwent a transient 30 or 120 min suture-occlusion of the middle cerebral artery (MCAO) followed by various reperfusion times (2 h, 1 d, 7 d, 30 d) or a permanent MCAO (1 d survival). Brains were characterized by TTC, thionine, and immunohistochemistry using MAP2, HSP72, and HSP27. TTC staining reliably identifies the infarct core at 1 d of reperfusion after 30 min MCAO and at all investigated times following 120 min and permanent MCAO. Nissl histology denotes the infarct core from 2 h up to 30 d after transient as well as permanent MCAO. Absent and attenuated MAP2 staining clearly identifies the infarct core and perilesional affected regions at all investigated times, respectively. HSP72 denotes perilesional areas in a limited post-ischemic time (1 d). HSP27 detects perilesional and remote impaired tissue from post-ischemic day 1 on. Furthermore a simultaneous expression of HSP72 and HSP27 in perilesional neurons was revealed.

CONCLUSIONS/SIGNIFICANCE

TTC and Nissl staining can be applied to designate the infarct core. MAP2, HSP72, and HSP27 are excellent markers not only to identify perilesional and remote areas but also to discriminate affected neuronal and glial populations. Moreover markers vary in their confinement to different reperfusion times. The extent and consistency of infarcts increase with prolonged occlusion of the MCA. Therefore interindividual infarct dimension should be precisely assessed by the combined use of different markers as described in this study.

Microarray‐based long‐term detection of genes differentially expressed after cortical spreading depression

Spreading depression (SD) is a slowly propagating wave of neuronal depolarization altering ion homeostasis, blood flow and energy metabolism without causing irreversible damage of the tissue. As SD has been implicated in several neurological diseases including migraine and stroke, understanding these disorders requires systematic knowledge of the processes modified by SD. Thus, we induced repetitive SD in the rat cerebral cortex by topical application of 3 m KCl for approximately 2 h and evaluated the kinetics of SD-induced changes in cortical gene expression for up to 30 days using Affymetrix RAE230A arrays. The temporal profile showed a rapid expression of immediate early genes, genes associated with inflammation, metabolism, stress and DNA repair, ion transport, and genes that play a role in growth/differentiation. Stress-response genes could still be detected after 24 h. At this time, induced genes were mainly related to the cell membrane and adhesion, or to the cytoskeleton. A subset of genes was still affected even 30 days after SD. Real-time polymerase chain reactions and immunohistochemistry confirmed the microarray results for several of the transcripts. Our findings demonstrate a temporal pattern of gene expression which might promote tissue remodeling and cortical plasticity, and might probably account for the mediation of neuronal tolerance towards subsequent ischemia.

Damage of serotonergic axons and immunolocalization of Hsp27, Hsp72, and Hsp90 molecular chaperones after a single dose of MDMA administration in Dark Agouti rat: Temporal, spatial, and cellular patterns

3,4-Methylenedioxymethamphetamine (MDMA, "ecstasy") causes long-term disturbance of the serotonergic system. We examined the temporal, spatial, and cellular distribution of three molecular chaperones, Hsp27, Hsp72, and Hsp90, 3 and 7 days after treatment with 7.5, 15, and 30 mg/kg single intraperitoneal (i.p.) doses of MDMA in Dark Agouti rat brains. Furthermore, we compared the immunostaining patterns of molecular chaperones with serotonergic axonal-vulnerability evaluated by tryptophan-hydroxylase (TryOH) immunoreactivity and with astroglial-activation detected by GFAP-immunostaining. There was a marked reduction in TryOH-immunoreactive axon density after MDMA treatment in all examined areas at both time points. Three days after treatment, a significant dose-dependent increase in Hsp27-immunoreactive protoplasmic astrocytes was found in the cingulate, frontal, occipital, and pyriform cortex, and in the hippocampus CA1. However, there was no increase in astroglial Hsp27-immunoreactivity in the caudate putamen, lateral septal nucleus, or anterior hypothalamus. A significant increase in the GFAP immunostaining density of protoplasmic astrocytes was found only in the hippocampus CA1. In addition, numerous strong Hsp72-immunopositive neurons were found in some brain areas only 3 days after treatment with 30 mg/kg MDMA. Increased Hsp27-immunoreactivity exclusively in the examined cortical areas reveals that Hsp27 is a sensitive marker of astroglial response to the effects of MDMA in these regions of Dark Agouti rat brain and suggests differential responses in astroglial Hsp27-expression between distinct brain areas. The co-occurrence of Hsp27 and GFAP response exclusively in the hippocampus CA1 may suggest the particular vulnerability of this region. The presence of strong Hsp72-immunopositive neurons in certain brain areas may reflect additional effects of MDMA on nonserotonergic neurons.

The role of heat shock proteins Hsp70 and Hsp27 in cellular protection of the central nervous system

Heat shock proteins (Hsps) are highly conserved and under physiological conditions act as molecular chaperones and/or have anti-apoptotic activities. Expression in the brain of two heat shock proteins, the70 kDa Hsp (Hsp70) and the 27 kDa Hsp (Hsp27), is notable because both proteins are highly inducible in glial cells and neurons following a wide range of noxious stimuli including ischemia, epileptic seizure and hyperthermia. In the central nervous system, constitutive expression of Hsp27 is limited to many (but not all) sensory and motor neurons of the brain stem and spinal cord, while there is little or no constitutive expression of Hsp70. However, inducible expression of both Hsp70 and Hsp27 is present in many areas of the brain and retina and is associated with cellular resistance to a variety of insults. The potential for manipulating the expression levels of Hsps for therapeutic advantage in neurodegenerative diseases such as Alzheimer's disease, stroke and glaucoma will be explored.

Heat shock protein modulation of KATPand KCachannel cerebrovasodilation after brain injury

Fluid percussion brain injury (FPI) impairs pial artery dilation to activators of the ATP-sensitive (KATP) and calcium-activated (KCa) K+channels. This study investigated the role of heat shock protein (HSP) in the modulation of K+channel-induced pial artery dilation after FPI in newborn pigs equipped with a closed cranial window. Under nonbrain injury conditions, topical coadministration of exogenous HSP-27 (1 μg/ml) blunted dilation to cromakalim, CGRP, and NS-1619 (10−8and 10−6M; cromakalim and CGRP are KATPagonists and NS-1619 is a KCaagonist). In contrast, coadministration of exogenous HSP-70 (1 μg/ml) potentiated dilation to cromakalim, CGRP, and NS-1619. FPI increased the cerebrospinal fluid (CSF) concentration of HSP-27 from 0.051 ± 0.012 to 0.113 ± 0.035 ng/ml but decreased the CSF concentration of HSP-70 from 50.42 ± 8.96 to 30.9 ± 9.9 ng/ml at 1 h postinsult. Pretreatment with topical exogenous HSP-70 (1 μg/ml) before FPI fully blocked injury-induced impairment of cromakalim and CGRP dilation and partially blocked injury-induced impairment of dilation to NS-1619. These data indicate that HSP-27 and HSP-70 contribute to modulation of K+channel-induced pial artery dilation. These data suggest that HSP-70 is an endogenous protectant of which its actions may be unmasked and/or potentiated with exogenous administration before brain injury.

Bilateral, vascular and perivascular glial upregulation of heat shock protein-27 after repeated epileptic seizures

Heat shock protein-27 (HSP-27) is an inducible stress response protein. It inhibits apoptotic cell death and is a reliable marker for oxidative stress. We studied the induction of HSP-27 in rat brains on days 1, 4 and 14 after repeated, pentylenetetrazole (PTZ)-induced seizures using immunohistochemisty. Saline treated control rats showed no induction of HSP-27. HSP-27 reactive astrocytes were rarely seen 1 or 4 days after PTZ injection. When present, single astrocytes were located in the cortex and/or the hippocampus. After 14 days PTZ treatment, a bilateral distribution of HSP-27 immunoreactive glia was present in piriform and entorhinal cortices and in the dentate gyrus of most brains. Rats with most intense HSP-27 upregulation showed HSP-27 in amygdala and thalamic nuclei. Astrocytes associated with blood vessels presented strongest HSP-27 staining, but did not show upregulation of gial fibrillary acidic protein and none responded with HSP-47 expression. Additionally, HSP-27 immunoreactivity increased in the endothelial cells of blood vessels in the affected brain regions, although no neuronal induction occurred. Contrastingly, a subconvulsive dose of the glutamine synthetase inhibitor L-methionine sulfoxime, which acts directly on astrocytes, resulted in a rapid, homogeneous astrocyte-specific HSP-27 upregulation within 24 h. Thus, repeated PTZ-induced seizure activity elicits a focal "heat shock" response in endothelial cells and astrocytes of selected cerebral regions indicating that expression of HSP-27 occurred in a seizure-dependent manner within the affected cerebral circuitries. Therefore, this PTZ-model of repeated seizure activity exhibited a cortical pattern of HSP-27 expression which is most comparable to that known from patients with epilepsy.

1α,25-Dihydroxy-vitamin D3 in combination with 17β-estradiol lowers the cortical expression of heat shock protein-27 following experimentally induced focal cortical ischemia in rats

1alpha,25-(OH)(2)-vitamin-D(3) (1,25-D(3)) and 17beta-estradiol are both known to act neuroprotective in certain experimental in vitro and in vivo settings. We studied the effects of 1,25-D(3) or 17beta-estradiol or their combined application on heat shock protein-27 (HSP-27) distribution after focal cortical ischemia using the photothrombosis model. HSP-27 is a well-established marker of the cerebral oxidative stress response and a potent inhibitor of apoptosis. Lesioned rats were injected i.p. one hour after injury with either 1 microg 1,25-D(3)/kg or 7 microg 17beta-estradiol/kg or a combination of both steroids. Groups of non-lesioned steroid-treated rats and lesioned, solvent-treated rats served as controls. Treatment with both steroids did not affect the size of the lesion. In addition, 17beta-estradiol resulted in significant reduction of HSP-27 induction, whereas the combination of 1,25-D(3)+17beta-estradiol resulted in a highly significant reduction of HSP-27 within the infracted cerebral cortex, indicating that both steroids act synergistically in a protective manner.

Cortical spreading depression augments kynurenate levels and reduces malonate toxicity in the rat cortex

Cortical spreading depression (CSD) is characterized by slowly propagating neuronal and astrocytic depolarization, resulting in transient, heightened resistance to subsequent neuronal injury. This study was designed to examine a possible role of the endogenous neuroprotective agent kynurenate (KYNA) in this phenomenon. Unilateral, consecutive CSDs, induced by topical application of 2 M KCl to the cortical surface of adult male rats, resulted in an ipsilateral increase (201-222% compared to controls) in KYNA levels, which was observed in the frontal, parietal and occipital cortex but not in other brain areas. This effect peaked on day 3 after CSD, and KYNA levels returned to normal on day 7. In separate rats, the lesion caused by an intracortical microinjection of the indirect excitotoxin malonate (500 nmol/0.5 microl) on days 1, 3 or 7 after CSD was reduced by 56-75% in the ipsilateral hemisphere. In normal rats, single or multiple injections of the kynurenine 3-hydroxylase inhibitor 4,5-dichlorobenzoylalanine (PNU 156561; 50 mg/kg, i.p.), which results in selective increases in brain KYNA levels, failed to protect cortical neurons against a focal malonate injection. Taken together, these findings indicate that the observed increase in brain KYNA is not responsible for CSD-induced tolerance to malonate-induced neuronal damage.

Translation-state analysis of gene expression in mouse brain after focal ischemia

Confounding any genome-scale analysis of gene expression after cerebral ischemia is massive suppression of protein synthesis. This inefficient translation questions the utility of examining profiles of total transcripts. Our approach to such postischemic gene profiling in the mouse by microarray analysis was to concentrate on those mRNAs bound to polyribosomes. In our proof-of-principle study, polysomally bound and unbound mRNAs were subjected to microarray analysis: of the 1,161 transcripts that we found to increase after ischemia, only 36% were bound to polyribosomes. In addition to the expected increases in heat-shock proteins and metallothioneins, increases in several other bound transcripts involved in the promotion of cell survival or antiinflammatory behavior were noted, such as CD63 (Lamp3), Lcn2 (lipocalin-2), Msn (moesin), and UCP2 (uncoupling protein 2), all of which showed increases in cognate protein by Western blotting. The list of heretofore nonfunctionally annotated transcripts (RIKEN clones/ESTs) that increased appeared to be novel. How some transcripts are selected in ischemic brain for translation into protein, while others are rejected, is not clear. The length of the 5'-UTR in the ischemically induced transcripts that occur in the NCBI RefSeq database did not indicate any general tendency to be more than 200 nt, nor to be longer than the 5'-UTRs of the unbound transcripts. Thus, the presence of a complex 5'-UTR region with internal ribosome entry sites (IRES) or polypyrimidine tracts (TOP) does not appear to be the basis of selection for translation in ischemic brain.

Time course and cellular distribution of hsp27 and hsp72 stress protein expression in a quantitative gerbil model of ischemic injury and tolerance: thresholds for hsp72 induction and hilar lesioning in the context of ischemic preconditioning

The distribution and time course of expression of the heat shock/stress proteins, hsp27 and hsp72, were evaluated in a highly controlled gerbil model of ischemic injury and tolerance induction, in which the duration of ischemic depolarization in each hippocampus provides a precise quantitative index of insult severity. Gerbils were subjected to brief priming insults (2- to 3.5-minute depolarization) that produce optimal preconditioning, to severe test insults (6- to 8.5-minute depolarization) that produce complete CA1 neuron loss in naive animals, or to combined insults administered 1 week apart, after which almost complete tolerance to CA1 neuron injury is observed. Immunoreactivities of hsp27, hsp72, glial fibrillary acidic protein and microtubule-associated protein 2 (MAP2) were evaluated in animals perfused at defined intervals after the final insult in each treatment group, using a variation of established antigen-retrieval procedures that significantly improves detection of many proteins in vibratome brain sections. Hsp72 was detected in CA1 neurons of some hippocampi 2 to 4 days after preconditioning, but this was only seen after the longest priming depolarizations, whereas shorter insults that still induced optimal tolerance failed to induce hsp72. Hsp72 was induced after test insults in preconditioned hippocampi, but at a higher depolarization threshold than observed for naive animals. An astrocytic localization of hsp27 was observed in regions of neuron injury, as indicated by reduced MAP2 immunoreactivity, and was primarily restricted to dentate hilus after preconditioning insults. These results establish that limited hilar lesions are characteristic of optimal preconditioning, whereas prior neuronal expression of either hsp72 or hsp27 is not required for ischemic tolerance.

Nestin expression after experimental intracerebral hemorrhage

The current study examines nestin expression after intracerebral hemorrhage (ICH), the role of different blood components in nestin upregulation, and the possibility that low doses of thrombin that induce tolerance to brain injury (thrombin preconditioning) might also induce nestin expression. Adult male Sprague-Dawley rats received an intracaudate injection of either whole blood, thrombin (1 or 5 U) or red blood cells (RBCs). Animals were sacrificed for single and double labeling immunohistochemistry to identify which cells express nestin, and for Western blotting to quantify nestin expression. By immunohistochemistry, nestin immunoreactivity was present in large numbers of astrocytes, surrounding the hematoma from day 3 to 1 week after ICH. After 2 weeks, nestin immunoreactivity was co-localized with a neuronal marker (neuronal specific enolase). By Western blot analysis, nestin was strongly expressed at day 3 (P<0.01) and 1 week (P<0.01), and expression persisted for at least 1 month (P<0.05). Intracerebral injection of thrombin or lysed RBCs resulted in a marked increase in nestin expression. Interestingly, injection of a low dose of thrombin that induces brain tolerance also upregulated nestin. The ICH-induced nestin expression in astrocytes may reflect an early response of these cells to injury, while the delayed expression in neurons might be a part of the adaptative response to injury perhaps leading to recovery of function. Nestin induction by a low dose of thrombin suggests that specific receptor-mediated pathways are involved in inducing nestin expression and that nestin may play a role in thrombin preconditioning.

Induction of Hsp27 and Hsp32 stress proteins and vimentin in glial cells of the rat hippocampus following hyperthermia

In response to stressful stimuli, cells respond by inducing a set of heat shock (stress) proteins (hsps) that play important roles in repair and protective mechanisms. The present study investigates the expression patterns of Hsp27 and Hsp32 in the adult rat hippocampus following whole body hyperthermia. A pronounced induction of these low-molecular-weight stress proteins was apparent in populations of glial cells such as astrocytes and microglia that were identified using cell-specific markers (GFAP for astrocytes and the lectin GSA I-B4 for microglia). Hyperthermia also resulted in a robust induction of the intermediate filament protein, vimentin, in glial cells in the adult rat hippocampus. Interestingly, a rapid induction of both Hsp27 and vimentin was observed in the microvasculature, suggesting that hyperthermic stress may compromise the blood-brain barrier.

Temporal expression of immunoreactivity for heat shock protein 25 (Hsp25) in the rat periodontal ligament following transection of the inferior alveolar nerve

The present study examined the immunohistochemical localization of heat shock protein 25 (Hsp25) during the regeneration of nerve fibers and Schwann cells in the periodontal ligament of the rat lower incisor following transection of the inferior alveolar nerve. In the untreated control group, the periodontal ligament of rat incisor did not contain any Hsp25-immunoreaction. On postoperative day 3 (PO 3d), a small number of Schwann cells with slender cytoplasmic processes exhibited Hsp25-immunoreactivity. From PO 5d to PO 21d, Hsp25-positive nerve fibers and Schwann cells drastically increased in number in the alveolar half of the ligament. Although the axons of some regenerating Ruffini-like endings also showed Hsp25-immunoreactions, the migrated Schwann cells were devoid of Hsp25-immunoreaction. Thereafter, Hsp25-positive structures decreased in number gradually to disappear from the periodontal ligament by PO 56d. This temporal expression of Hsp25 in the periodontal ligament well-reflected the regeneration process of the nerve fibers. Hsp25 in the regenerating nerve fibers and denervated Schwann cells most likely serves in modulating actin dynamics and as a cellular inhibitor of apoptosis, respectively.

Administration of brain-derived neurotrophic factor suppresses the expression of heat shock protein 27 in rat retinal ganglion cells following axotomy

Optic nerve transection results in the apoptotic cell death of the majority of retinal ganglion cells by 14 days. The neurotrophin brain-derived neurotrophic factor (BDNF) enhances survival of retinal ganglion cells. In addition, the small heat shock protein Hsp27, with its anti-apoptotic effects, may be important for neuron survival following axotomy or trophic factor withdrawal. We recently reported the induction and expression of Hsp27 in a subset of retinal ganglion cells following axotomy. Here we have examined the effect of BDNF administration on the expression of Hsp27 in axotomized adult rodent retinal ganglion cells. Retinal ganglion cells were pre-labeled with Fluorogold prior to optic nerve transection and concomitant intraocular injection of BDNF or vehicle. Hsp27 immunofluorescence was examined in retinal sections from 4 to 28 days following injury. Consistent with previous survival studies, the number of Fluorogold-labeled retinal ganglion cells declined from 100% at 4 days to approximately 15% by 14 days following axotomy and vehicle injection. In contrast, with BDNF administration, retinal ganglion cell survival was maintained at 100% to 7 days following axotomy. We report that the number of Hsp27-positive injured retinal ganglion cells, as detected by immunohistochemical staining, was decreased by 50% in BDNF-treated retinas, when compared with vehicle-treated controls. This decreased expression of Hsp27 in response to BDNF treatment was seen both at early (4 days) and delayed (14 days) times. BDNF following optic nerve transection significantly reduced the expression of Hsp27 in retinal ganglion cells. These results indicate that BDNF may down-regulate alternate cell survival pathways, including the stress-induced expression of Hsp27, and may help to explain the failure of chronic neurotrophin treatment to maintain long-term retinal ganglion cell survival.

Delayed, but prolonged increases in astrocytic clusterin (ApoJ) mRNA expression following acute cortical spreading depression in the rat: evidence for a role of clusterin in ischemic tolerance

Clusterin is a sulfated glycoprotein produced by neurons and by resting and activated astrocytes that has several putative functions, including protective responses to brain injury. Cortical spreading depression (CSD) is a powerful yet largely benign stimulus that acutely is capable of providing long-lasting ischemic tolerance. The current study investigated possible alterations in expression of clusterin mRNA in the cerebral cortex of the rat at various times after unilateral CSD. Using semiquantitative in situ hybridization histochemistry, significant increases (30-100%; P< or =0.05) in clusterin mRNA were detected in layers I-III and IV-VI of the ipsilateral cortex at 1, 2, 7 and 14 (layers I-III only) days after CSD. Transcript levels in the ipsilateral cortex were again equivalent to contralateral (control) levels at 28 days after CSD. These molecular anatomical studies also revealed that both neurons and nonneuronal cells (presumed reactive astrocytes) increased their expression of clusterin mRNA following CSD. Notably the time-course of increases in clusterin mRNA after CSD (1-14 days) overlaps that during which CSD reportedly provides neuroprotection against subsequent cerebral ischemia. These findings along with other evidence suggest that increased clusterin production and secretion, particularly by astrocytes, could be neuroprotective-perhaps via one or more of its putative actions that include inhibition of complement activation and cytolysis, effects on chemotaxis and apoptosis, and actions as an anti-stress protein chaperone.

HSP27 is markedly induced in Schwann cell columns and associated regenerating axons

It is well known that regenerating axons enter Schwann cell (SC) columns, within which they grow to reinnervate the appropriate targets. The current study detected a marked induction of a 27-kDa heat shock protein (HSP27) in the SC columns of crush-injured rat sciatic nerves. Immunohistochemical studies showed the first appearance of strong HSP27-immunoreactive linear structures in the proximal stump near an injury site 7 h after an operation. The HSP27-immunoreactive linear structures crossed the injury site to the distal stump 2 days after the operation. They then extended in a more proximal and more distal direction and were found to have propagated through the entire length of the nerve 1 week after the operation. This pattern of expression was maintained until 3 weeks after the operation. Double-immunofluorescent labeling and confocal laser microscopy confirmed that the linear structures consisted of SC columns and associated multiple axons. The HSP27-immunoreactive SC columns expressed glial fibrillary acidic protein, but not S-100 protein. Electron microscopy and immunoelectron microscopy demonstrated that reactive Schwann cells (SCs) and the associated axons with an outgrowing profile exhibited a strong immunoreactivity to HSP27, with the former containing a greater number of bundles of intermediate filaments. It is suggested that HSP27 may play an essential role in axonal outgrowth, especially by contributing to cytoskeletal dynamics in SCs.

Injury to retinal ganglion cells induces expression of the small heat shock protein Hsp27 in the rat visual system

Optic nerve transection results in apoptotic cell death of most adult rat retinal ganglion cells that begins at 4 days and leaves few surviving neurons at 14 days post-injury [Berkelaar et al. (1994) J. Neurosci. 14, 4368-4374]. The small heat shock protein Hsp27 has recently been shown to play a role in sensory neuron survival following peripheral nerve axotomy [Lewis et al. (1999) J. Neurosci. 19, 8945-8953]. To investigate the role of Hsp27 in injured CNS sensory neurons, we have studied the induction and cell-specific expression of Hsp27 in rat retinal ganglion cells 1-28 days after optic nerve transection. Immunohistochemical results indicate that Hsp27 is not present at detectable levels in the ganglion cell layer of control (uninjured) or sham-operated control rats. In contrast, Hsp27 is detected in retinal ganglion cells from 4 to 28 days following axotomy. Furthermore, the percentage of surviving retinal ganglion cells that are Hsp27-positive increased over the same time period. Hsp27 is also detected in glial fibrillary acidic protein-positive astrocytes in the optic layer of the superior colliculus from 4 to 28 days after optic nerve transection. These experiments demonstrate that transection of the optic nerve results in the expression of Hsp27 in three distinct regions of the rat visual system: sensory retinal ganglion cells in the eye, glial cells of the optic tract, and astrocytes in the optic layer of the superior colliculus. Hsp27 may be associated with enhanced survival of a subset of retinal ganglion cells, providing evidence of a protective role for Hsp27 in CNS neuronal injury.

Genomic responses of the brain to ischemic stroke, intracerebral haemorrhage, kainate seizures, hypoglycemia, and hypoxia

RNA expression profiles in rat brain were examined 24 h after ischemic stroke, intracerebral haemorrhage, kainate-induced seizures, insulin-induced hypoglycemia, and hypoxia and compared to sham- or untouched controls. Rat oligonucleotide microarrays were used to compare expression of over 8000 transcripts from three subjects in each group (n = 27). Of the somewhat less than 4000 transcripts called 'present' in normal or treated cortex, 5-10% of these were up-regulated 24 h after ischemia (415), haemorrhage (205), kainate (187), and hypoglycemia (302) with relatively few genes induced by 6 h of moderate (8% oxygen) hypoxia (15). Of the genes induced 24 h after ischemia, haemorrhage, and hypoglycemia, approximately half were unique for each condition suggesting unique components of the responses to each of the injuries. A significant component of the responses involved immune-process related genes likely to represent responses to dying neurons, glia and vessels in ischemia; to blood elements in haemorrhage; and to the selectively vulnerable neurons that die after hypoglycemia. All of the genes induced by kainate were also induced either by ischemia, haemorrhage or hypoglycemia. This strongly supports the concept that excitotoxicity not only plays an important role in ischemia, but is an important mechanism of brain injury after intracerebral haemorrhage and hypoglycemia. In contrast, there was only a single gene that was down-regulated by all of the injury conditions suggesting there is not a common gene down-regulation response to injury.

Glial expression of small heat shock proteins following an excitotoxic lesion in the immature rat brain

Heat shock proteins (HSPs) are chaperones induced under pathological conditions and involved in protein stabilization and cellular protection. In this study, we have evaluated the expression pattern of the glial cell-related HSP27, HSP32, and HSP47 following an excitotoxic lesion in the immature rat brain. Postnatal day 9 rats received an intracortical injection of N-methyl-D-aspartate and tissue was processed immunohistochemically for HSPs and double labeling using astroglial and microglial markers. HSP expression was quantified by image analysis. Excitotoxic damage caused primary cortical degeneration and secondary damage in the corresponding thalamus. In the injured cortex, reactive microglia/macrophages expressed HSP32 from 10 h until 14 days postlesion (PL), showing maximal levels at days 3-5. In parallel, most cortical reactive astrocytes showed expression of HSP47 from 10 h until 14 days PL and a population of them also displayed HSP27 labeling from 1 day PL. In addition, some cortical reactive astrocytes showed a temporary expression of HSP32 at day 1. In general, astroglial HSP expression in the cortex achieved maximal levels at days 3-5 PL. In the damaged thalamus, HSP32 was not significantly induced, but reactive astrocytes expressed HSP47 and some of them also HSP27. Thalamic astroglial HSP induction was transient, peaked at 5 days PL and reached basal levels by day 14. The injury-induced expression of HSP32, HSP27, and HSP47 in glial cells may contribute to glial cell protection and adaptation to damage, therefore playing an important role in the evolution of the glial response and the excitotoxic lesion outcome. HSP32 may provide antioxidant protective mechanisms to microglia/macrophages, whereas HSP47 could contribute to extracellular matrix remodeling and HSP27 may stabilize the astroglial cytoskeleton and participate in astroglial antioxidant mechanisms.

Effects of global cerebral ischemia and preconditioning on heat shock protein 27 immunocontent and phosphorylation in rat hippocampus

Global cerebral ischemia, with or without preconditioning, leads to an increase in heat shock protein 27 (HSP27) immunocontent and alterations in HSP27 phosphorylation in CA1 and dentate gyrus areas of the hippocampus. We studied different times of reperfusion (1, 4, 7, 14, 21 and 30 days) using 2 min, 10 min or 2+10 min of ischemia. The results showed an increase in HSP27 immunocontent of about 300% after 10 min of ischemia in CA1 and dentate gyrus. CA1, a hippocampal vulnerable area, showed an increase in HSP27 phosphorylation, parallel with immunocontent. In dentate gyrus, a resistant area, the increase in HSP phosphorylation was lower than immunocontent. After preconditioned ischemia (2+10 min), when CA1 neurons are protected to a lethal, 10 min insult, we observed an increase in HSP immunocontent and a decrease in phosphorylation in both regions of the hippocampus, suggesting that, when there is no neuronal death, HSP27 in a vulnerable area responds similarly to the resistant area.When dephosphorylated, HSP27 acts as a chaperone, protecting other proteins from denaturation. As it is markedly expressed in astrocytes, we suggest that HSP27 could be protecting hippocampal astrocytes, which could then be helping neurons to resist to the insult, maintaining tissue normal homeostasis.

Expression of 27 kDa heat shock protein (Hsp27) in immature rat brain after a cortical aspiration lesion

The 27 kDa heat shock protein (Hsp27) is a well-known member of the astroglial response to injury, playing a protective role against oxidative stress, apoptosis, and cytoskeletal destruction. Although several studies have been focused on the damaged adult brain, little is known about Hsp27 expression in the immature brain. In this work, we have examined the spatiotemporal pattern of Hsp27 expression in the normal postnatal rat brain following a cortical aspiration lesion at postnatal day 9. In the immature brain, Hsp27 is mainly observed in the internal capsule, although some scattered cells are also found in the ependyma, the corpus callosum, the septum, and hypothalamic glia limitans. In the internal capsule, Hsp27 expression is developmentally regulated, being significantly decreased from postnatal day 14. After a cortical aspiration lesion, de novo expression of Hsp27 is observed in cortical injured areas as well as in the secondary affected thalamus. In the cortex, expression of Hsp27 is first seen at day 1 postlesion (PL) surrounding the neurodegenerative area, becoming restricted to the glial scar at longer survival times. Although a pulse-like expression of Hsp27 is observed in some microglial cells at day 1 PL, most Hsp27-labeled cells are reactive astrocytes, which show GFAP overexpression and coexpress vimentin from day 3 PL. In the thalamus, astroglial Hsp27 expression is delayed, being first observed at day 5 PL. Thalamic Hsp27-labeled astrocytes do not show vimentin expression. Our observations demonstrate astroglial expression of Hsp27 in areas of tissue damage following postnatal traumatic injury, suggesting an involvement of this cytoskeleton-stabilizing protein in the remodeling processes following postnatal brain damage.

Preconditioning with cortical spreading depression does not upregulate Cu/Zn-SOD or Mn-SOD in the cerebral cortex of rats

Previous studies have demonstrated that preconditioning the brain with cortical spreading depression (CSD) induces tolerance to a subsequent episode of ischemia. In other models of preconditioning, induction of ischemic tolerance has been associated with increased expression of the antioxidant enzyme, superoxide dismutase (SOD). The objective of the present study was to determine whether CSD upregulates Cu/Zn-SOD or Mn-SOD. CSD was induced in one hemisphere by applying 2 M KCl to the frontal cortex in Wistar rats. After 2 or 24 h of recovery, Cu/Zn-SOD and Mn-SOD mRNA levels were determined in both hemispheres using Northern blot analysis. In separate rats, Cu/Zn-SOD and Mn-SOD protein levels were determined 24 and 72 h after CSD using Western blot analysis. In addition, total SOD, Cu/Zn-SOD and Mn-SOD enzymatic activities were measured 24 and 72 h after CSD using spectrophotometric and zymographic assays. At the times investigated, no significant differences in mRNA or protein levels for Cu/Zn-SOD or Mn-SOD were observed between the ipsilateral and contralateral cortex. Further, there were no significant differences in Cu/Zn-SOD or Mn-SOD enzymatic activities between the two hemispheres at 24 or 72 h after CSD. In addition, CSD did not alter the activities of Cu/Zn-SOD or Mn-SOD in either hemisphere, relative to those in unoperated animals. Taken together, these results fail to support the hypothesis that CSD-induced tolerance is mediated through the upregulation of Cu/Zn-SOD or Mn-SOD.

Isoform-specific membrane translocation of protein kinase C after ischemic preconditioning

Mild cerebral anoxic/ischemic/stress insults promote 'tolerance' and thereby protect the brain from subsequent 'lethal' anoxic/ischemic insults. We examined whether specific activation of PKC alpha, delta, epsilon, or zeta isoforms is associated with ischemic preconditioning (IPC) in rat brain. IPC was produced by a 2-minute global cerebral ischemia. Membrane and cytosolic fractions of the hippocampi were immunoblotted using specific antibodies for PKCalpha, delta, epsilon, and zeta. PKCalpha showed a significant translocation to the membrane fraction from 30 min to 4 h and PKCdelta at 4 h following IPC. In contrast, the membrane/cytosol ratio of PKCepsilon showed a tendency to decrease at 30 min and 8 h, and the membrane/cytosol ratio of PKCzeta was significantly decreased from 30 min to 24 h following IPC. These findings indicate PKC isoform-specific membrane translocations in the hippocampus after brief global brain ischemia and suggest that activation of PKCalpha and PKCdelta may be associated with IPC-induced tolerance in the rat hippocampus.

Thrombin preconditioning, heat shock proteins and thrombin-induced brain edema

Intracerebral injections of high concentrations of thrombin cause brain edema but, in vitro, low concentrations of thrombin may be neuroprotective. This study investigated whether a low dose of thrombin might induce tolerance to subsequent large doses of thrombin (thrombin preconditioning; TPC) in a manner analogous to ischemic preconditioning. The study involved five parts. The first tested the effect of intracerebral infusion of a small dose (1 U) of thrombin on brain water content. In the second part, the effect of such a small dose of thrombin on subsequent edema formation from a large dose of thrombin (5 U) was evaluated. The time course of TPC was examined in the third part. In the fourth part, heat shock protein (HSP) 27, HSP32 and HSP70 were quantitated by Western blotting analysis while the fifth identified the cell types expressing HSPs. Injection of a low dose of thrombin alone did not cause brain edema. However, TPC significantly attenuated the edema induced by a subsequent injection of a large dose of thrombin. This effect of TPC was abolished by co-injection of a thrombin inhibitor, hirudin. The maximal effect of TPC on edema formation was seven days after pretreatment. This time course was similar to that for a marked up-regulation in astrocytic HSP27. TPC also induced HSP32, but this effect occurred earlier than the effect on edema formation. TPC had no effect on HSP70. These results suggest that thrombin-induced brain tolerance may be related to HSP27 induction.

Induction of colligin may attenuate brain edema following intracerebral hemorrhage

Brain edema plays an important role in the secondary brain injury following intracerebral hemorrhage (ICH). Edema formation after ICH has been linked to thrombin toxicity. Therefore, the induction of endogenous serine protease inhibitors, which inhibit thrombin prior to ICH may limit edema formation. This study examines whether injection of a low dose of thrombin upregulates such inhibitors and induces tolerance to subsequent ICH. Rats received intracerebral infusions of either one unit thrombin or saline into the right caudate nucleus. After seven days, the rats were either (A) used to examine colligin (a serine protease inhibitor) induction by Western blot analysis, immunohistochemistry and immunofluorescent double labeling, (B) to determine brain water content, or (C) they received a second injection of 50 microL blood and brain edema was determined one day later. Intracerebral infusion of thrombin caused a marked upregulation of colligin, a serine protease inhibitor, in the ipsilateral basal ganglia. Immunocytochemistry and immunofluorescent double labeling showed that colligin was induced in astrocytes. Infusion of this dose of thrombin alone did not affect brain water content but it significantly attenuated subsequent ICH-induced brain edema (79.0 +/- 0.5 vs. 81.4 +/- 0.9%, P < 0.01). Our results demonstrate that low doses of thrombin upregulate brain colligin levels and attenuate edema formation induced by ICH.

Induction of heat shock proteins and motor function deficits after focal cerebellar injury

A weight drop model of focal cerebellar injury was used to identify heat shock protein induction and motor function deficits in the anesthetized, adult male, Sprague-Dawley rat. All animals were trained on a beam walking test prior to surgery. Groups of animals received severe, mild or sham weight drop injury to the lateral/paravermal region of the cerebellum. The mild and sham-injured animals showed no motor deficits in the beam walking test, whereas animals with severe cerebellar injury showed significant motor deficits in the beam walking test that approached recovery of motor function 20 days after injury. Following severe injury, induction of heat shock protein of 27kDa was observed in Purkinje cells and in neurons of the deep cerebellar nuclei, as well as Bergmann glial cells, glial cells located in the granule cell layer and the underlying white matter. Following mild injury, heat shock protein of 27kDa induction was observed in Purkinje cells and glial cells, but not in neurons of the deep cerebellar nuclei. The labeled Purkinje cells were widely distributed in the ipsilateral cerebellar cortex. Many of the glial cells that were immunostained with heat shock protein of 27kDa co-localized with cells immunoreactive for glial fibrillary acidic protein. After severe injury, heat shock protein of 72kDa was localized mainly in granule cells at the site of the trauma and in the ipsilateral deep cerebellar nuclei whereas, after mild injury, light labeling was observed only in the granule cell layer. The results demonstrate that focal cerebellar injury has profound effects on motor behavior and induces different families of heat shock proteins in specific groups of neurons and glial cells in the cerebellum.

Dorsal horn lesion resulting from spinal root avulsion leads to the accumulation of stress-responsive proteins

The aim of this study was to demonstrate acute to subacute molecular episodes in the dorsal horn following root avulsion using immunohistochemical methods with the markers for synapses, astrocytes and such stress-responsive molecules as heat shock proteins (Hsps) and p38 MAP kinase (p38). Among them, Hsp27 was accumulated selectively in the injured substantia gelatinosa 24 h after avulsion injury. The localization of Hsp27 in astrocytes within the substantia gelatinosa was confirmed by the double immunofluorescence method using anti-Hsp27 antibody and either anti-synaptophysin antibody or anti-glutamine synthetase antibody and by immunoelectron microscopy for Hsp27. The pattern of Hsp27 expression subsequently changed from glial pattern to punctate pattern by 7 days. Immunoelectron microscopy revealed that the punctate pattern in the subacute stage corresponded to distal parts of the astrocytic processes. Hsp27 immunoreaction was decreased 21 days after root avulsion. In the distal axotomy model, Hsp27 was accumulated later in the ipsilateral dorsal horn in a punctate pattern from 7 days after the axotomy. Phosphorylation of p38 was detected in microglia in the dorsal horn following both avulsion and axotomy. Substance P was slightly decreased in the injured substantia gelatinosa in both the avulsion and axotomy models around 14-21 days. We conclude that Hsp27 is a useful marker for demonstrating dorsal horn lesions following avulsion injury and that avulsion injury may induce Hsp27 in the dorsal horn more rapidly than distal axotomy.

Constitutive expression of the 27-kDa heat-shock protein in neurons and satellite cells in the peripheral nervous system of the rat

By use of reverse transcriptase-polymerase chain reaction, abundant expression of the mRNA of 27 kDa heat shock protein (Hsp27) was revealed in the sympathetic and parasympathetic ganglia as well as in the sensory ganglia of unstressed adult rats. In situ hybridization and immunohistochemistry further localized Hsp27 mRNA and protein to both neurons and satellite cells in all types of ganglia examined. Schwann cells in the ganglia and peripheral nerve fibers were devoid of Hsp27 signal. These results suggested that Hsp27 is constitutively expressed in neurons and satellite cells in the entire peripheral nervous system of the rat.

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.

Diffusion- and perfusion-weighted magnetic resonance imaging of focal cerebral ischemia and cortical spreading depression under conditions of mild hypothermia

In a model of experimental stroke, we characterize the effects of mild hypothermia, an effective neuroprotectant, on fluid shifts, cerebral perfusion and spreading depression (SD) using diffusion- (DWI) and perfusion-weighted MRI (PWI). Twenty-two rats underwent 2 h of middle cerebral artery (MCA) occlusion and were either kept normothermic or rendered mildly hypothermic shortly after MCA occlusion for 2 h. DWI images were obtained 0.5, 2 and 24 h after MCA occlusion, and maps of the apparent diffusion coefficient (ADC) were generated. SD-like transient ADC decreases were also detected using DWI in animals subjected to topical KCl application (n=4) and ischemia (n=6). Mild hypothermia significantly inhibited DWI lesion growth early after the onset of ischemia as well as 24 h later, and improved recovery of striatal ADC by 24 h. Mild hypothermia prolonged SD-like ADC transients and further decreased the ADC following KCl application and immediately after MCA occlusion. Cerebral perfusion, however, was not affected by temperature changes. We conclude that mild hypothermia is neuroprotective and suppresses infarct growth early after the onset of ischemia, with better ADC recovery. The ADC decrease during SD was greater during mild hypothermia, and suggests that the source of the ADC is more complex than previously believed.

Conditioning effects of repetitive mild neurotrauma on motor function in an animal model of focal brain injury

A weight drop model of brain injury was used to determine the effects of repetitive mild brain injury on motor function, heat shock protein and glial fibrillary acidic protein expression in the anesthetized, adult male, Sprague-Dawley rat. Repetitive mild brain injury was produced when animals received a series of three mild injuries spaced three days apart. A separate group of repetitive mild injured animals also received a subsequent severe brain injury between three and five days after the last mild injury. All animals were trained on a beam-walking test prior to surgery. The mild, repetitive mild and repetitive mild plus severe brain injury groups showed no motor deficits in the beam-walking test, whereas the animals with only severe brain injury showed significant motor deficits (increase in number of footslips) in the beam-walking test that recovered within eight days after injury. Both repetitive mild plus severe injury and severe injury only animals had cortical necrotic cavities of similar size in the region of the hindlimb motor cortex. Both the repetitive mild and severe brain-injured animals had marked heat shock protein 27kDa and glial fibrillary acidic protein staining in the cerebral cortex. Fluoro-Jade, heat shock protein 27kDa and 72kDa labeling indicated that there were widespread effects on cortical, subcortical and spinal neurons and glial cells after repetitive mild brain injury. These results suggest that repetitive mild brain injury conditions the brain so that subsequent brain injury at the same site has no effect on motor function. Furthermore, repetitive mild injury-induced activation of processes distant to the primary injury site may have a role in activation of secondary sites involved in recovery of motor function.