Protective effect of LY379268, a selective group II metabotropic glutamate receptor agonist, on dizocilpine-induced neuropathological changes in rat retrosplenial cortex

In the present study, we examined the effects of LY379268, the group II metabotropic glutamate receptor (mGluR) agonist, on the neuropathological changes in the rat retrosplenial cortex induced by noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine ((+)-MK-801). Administration of LY379268 (1, 3, 10 mg/kg, i.p.) reduced dizocilpine (0.5 mg/kg, i.p.)-induced neuropathological changes in the retrosplenial cortex, in a dose-dependent manner. Co-administration of LY379268 (10 mg/kg, i.p.) with group II mGluR antagonist LY341495 (5 mg/kg, i.p.) blocked the effects of LY379268. Furthermore, LY379268 (10 mg/kg, i.p.) significantly reduced the expression of heat shock protein HSP-70, a marker of reversible neuronal injury, in the rat retrosplenial cortex after administration of dizocilpine (0.5 mg/kg, i.p.). Moreover, pretreatment with LY379268 (10 mg/kg, i.p.) significantly suppressed the increase in extracellular acetylcholine (ACh) levels in the retrosplenial cortex induced by administration of dizocilpine (0.5 mg/kg, i.p.). These results suggest that LY379268 has a protective effect on the neurotoxicity in the rat retrosplenial cortex after administration of NMDA receptor antagonists such as dizocilpine.     

Regionally different effects of scopolamine on NMDA antagonist-induced heat shock protein HSP70

Using immunohistochemical technique, we investigated the regionally different roles of muscarinic receptors in the induction of HSP-70 by NMDA receptor antagonists. The administration of memantine and phencyclidine induced HSP-70 in the retrosplenial cortex of rat brain. Pretreatment with the muscarinic receptor antagonist scopolamine (0.1–1 mg/kg) blocked induction of HSP-70 in layer III of the retrosplenial cortex. However, induction of HSP-70 in layer V was augmented by scopolamine. These results suggest a regional difference in the mechanism of neurotoxicity induced by NMDA receptor antagonists.     

Haloperidol Prevents Ketamine- and Phencyclidine-Induced HSP70 Protein Expression but Not Microglial Activation

NoncompetitiveN-methyl- -aspartate (NMDA) receptor antagonists, including ketamine and phencyclidine (PCP), produce abnormal intracellular vacuoles in posterior cingulate and retrosplenial cortical neurons in the rat. Ketamine also induces 70-kDa heat shock protein (HSP70) expression in pyramidal neurons in the posterior cingulate and retrosplenial cortex and, as shown by this study, activates microglia in the retrosplenial cortex of the rat. Whereas HSP70 protein expression was induced with ketamine doses of 40 mg/kg (ip) and higher, doses of 80 mg/kg and higher were required to activate microglia. HSP70-positive neurons were observed in 30- to 90-day-old rats but not in younger, 10- to 20-day-old animals following ketamine (80 mg/kg, ip). Pretreatment with the antipsychotic drug haloperidol at doses of 1.0 mg/kg and above abolished all HSP70 immunostaining produced by ketamine (80 mg/kg). However, a single dose of haloperidol (5 mg/kg, im) did not decrease the number of microglia activated in retrosplenial cortex by ketamine (80–140 mg/kg). Similarly, PCP (10 and 50 mg/kg, ip)-induced microglial activation in the posterior cingulate and retrosplenial cortex of adult rats was not blocked by haloperidol (10 mg/kg, im, 1 h prior to PCP). These results suggest that ketamine and PCP injure neurons in the posterior cingulate and retrosplenial cortex of adult rats. Though haloperidol may afford some protection against this injury since it inhibits induction of HSP70 expression, the failure to prevent microglial activation suggests that single doses of haloperidol do not completely protect neurons from NMDA antagonist toxicity.     

Bilateral blockade of NMDA receptors in anterior thalamus by dizocilpine (MK-801) injures pyramidal neurons in rat retrosplenial cortex

Non-competitive N-methyl-D-aspartate (NMDA) receptor antagonists, ketamine, phencyclidine (PCP) and dizocilpine (MK-801), produce psychosis in people. In rodents they produce cytoplasmic vacuoles in injured retrosplenial cortical neurons that express HSP70 heat shock protein. This study examined possible circuits and receptors that mediate this neuronal injury. Bilateral, but not unilateral, injection of dizocilpine (5, 10, 15, 20 microg/microL per side) into the anterior thalamus induced HSP70 protein in pyramidal neurons in deep layer III of rat retrosplenial cortex 24 h later. In contrast, bilateral dizocilpine injections (5, 10, 15, 20 microg/microL per side) into the retrosplenial cortex or into the diagonal band of Broca did not induce HSP70. Bilateral injections of muscimol (0.1, 1, 10 microg/microL per side), a GABAA (gamma-aminobutyric acid) agonist, into the anterior thalamus blocked HSP70 induction in the retrosplenial cortex produced by systemic dizocilpine (1 mg/kg). Bilateral thalamic injections of baclofen (0.1, 1, 10 microg/microL per side), a GABAB agonist, were ineffective. Anterograde tracer studies confirmed that neurons in the anterior thalamus project to superficial layer III of the retrosplenial cortex where the dendrites of HSP70-immunostained neurons in deep layer III reside. Bilateral blockade of NMDA receptors on GABA neurons in the reticular nuclei of the thalamus is proposed to decrease GABA neuronal firing, decrease GABA release and decrease activation of GABAA receptors. This activates thalamic projection neurons that damage retrosplenial cortical neurons presumably via unblocked cortical glutamate alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA) and kainate receptors. The increases of blood flow that occur in the thalamus and retrosplenial cortex of people that have psychosis produced by NMDA antagonists could be related to thalamic excitation of the retrosplenial cortex produced by these drugs.     

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

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

Expression of cyclooxygenase-2 mRNA in rat retrosplenial cortex following administration of phencyclidine

The effect of NMDA receptor antagonist phencyclidine (PCP) on expression of cyclooxygenase (COX)-2 mRNA in the rat brain was studied. Administration of PCP (12.5, 25 or 50 mg/kg, i.p., 6 h) caused marked induction of COX-2 mRNA and heat shock gene hsp-70 mRNA, a marker of neuronal injury, in the retrosplenial cortex, in a dose-dependent manner. These results suggest that COX-2 may play a role in the neurotoxicity of NMDA receptor antagonists.     

Fluoxetine prevents PCP- and MK801-induced HSP70 expression in injured limbic cortical neurons of rats.

BACKGROUND: N-Methyl-D-aspartate (NMDA) receptor antagonists, including phencyclidine (PCP) and dizocilpine (MK801), cause schizophrenialike psychosis in humans, and produce vacuolated neurons in the cingulate and retrosplenial cortices of the rat brain. Since psychotically depressed patients and schizophrenic depressed patients may require treatment with selective serotonin reuptake inhibitors (SSRIs), it is of interest to examine the relationship between SSRIs and NMDA antagonist neurotoxicity. METHODS: The neurotoxicity of PCP and MK801 was assessed using heat shock protein (HSP70) immunocytochemistry and HSP70 Western blots because HSP70 is expressed in the injured, vacuolated neurons. Female rats were given fluoxetine (0, 5, 10, and 20 mg/kg IP) followed 1 hour later by MK801 (1 mg/kg IP) or PCP (50 mg/kg IP). RESULTS: Pretreatment with fluoxetine (20 mg/kg IP) 1 hour before MK801 prevented the induction of HSP70 by MK801 in the cingulate and retrosplenial cortices. Pretreatment with fluoxetine (10 or 20 mg/kg IP) 1 hour before PCP also prevented the HSP70 induction by PCP. CONCLUSIONS: Fluoxetine prevents the neurotoxicity of NMDA receptor antagonists in rat brain. This suggests the possibility that SSRIs could modulate psychosis, and may provide a model for examining the link between the hallucinogenic properties of PCP and lysergic acid diethylamide.     

MK-801 neurotoxicity in the guinea pig cerebral cortex: Susceptibility and regional differences compared with the rat

N-methyl-D-aspartate (NMDA) receptor antagonists induce transient vacuole formation in neurons of the retrosplenial cortex and, after higher doses, necrosis in the same region. To our knowledge, all studies demonstrating these effects have been carried out in rats or mice. The present study investigated whether vacuolization occurs in the guinea pig, rats being used as controls. Female Dunkin-Hartley guinea pigs (age 15–18 weeks) were given a single subcutaneous injection of saline or the non-competitive NMDA antagonist dizocilpine maleate [(+)-MK-801; 1, 4, or 12 mg/kg]. Female Sprague-Dawley rats (age 16 weeks) received saline or MK-801 (1 mg/kg). Whatever the dose of MK-801, guinea pigs showed only occasional vacuolated neurons in the retrosplenial cortex. However, affected neurons (mainly large pyramidal cells of layer V) were found in the frontoparietal neocortex. The reaction was limited after 1 mg/kg, and seemed to reach a maximum at 4 mg/kg. Rats injected with 1 mg/kg MK-801 showed an intense vacuole reaction in neurons from layers III–IV of the retrosplenial cortex, but no affected neurons were noted in neocortical areas. We conclude that there are significant species differences in susceptibility to, and location of, vacuolization induced by NMDA receptor antagonists. J. Neurosci. Res. 49:364–371, 1997. © 1997 Wiley-Liss, Inc.     

Memantine induces heat shock protein HSP70 in the posterior cingulate cortex, retrosplenial cortex and dentate gyrus of rat brain

High-affinity N-methyl-d-aspartate (NMDA) receptor antagonists like MK-801 are known to induce the heat shock. protein, HSP70, in the posterior cingulate cortex and retrosplenial cortex of rat brain. Memantine, which is a low affinity uncompetitive NMDA receptor antagonist, has been used in the treatment of Parkinson's disease in Europe. The faster kinetics of memantine in blocking and unblocking the NMDA receptor-operated ion channel as opposed to high-affinity NMDA antagonists like MK-801 has been thought to account for the safety of memantine. The present study evaluated the neurotoxic potential of memantine and amantadine using the induction of HSP70 immunoreactivity in rat brain. Memantine (25, 50, 75 mg/kg) induced HSP70 in the posterior cingulate, retrosplenial cortex and dentate gyrus of rat brain. In contrast, amantadine (50, 100, 200 mg/kg) did not induce HSP70 in the rat brain. These results suggest that memantine has an antagonistic effect at NMDA receptor in vivo, and raises the possibility that high doses of memantine may cause neuronal damage similar to those observed with other high-affinity NMDA receptor antagonists.     

Neuronal vacuole formation in the rat posterior cingulate/retrosplenial cortex after treatment with the N-methyl-d-aspartate (NMDA) antagonist MK-801 (dizocilpine maleate)

Cytoplasmic vacuoles appear in neurons of the posterior cingulate/retrosplenial cortex (PC/RS) of rats after treatment with N-methyl-d-aspartate (NMDA) receptor antagonists. Prominent dilatation of mitochondria and endoplasmic reticulum has been described within 2 h; however, the ultrastructural features of vacuole formation are unknown. To investigate this, the present study examined the PC/RS cortex of male rats (age 60–70 days) at 15, 30, 45, 60, 90, and 120 min after subcutaneous treatment with 1 mg/kg of the noncompetitive NMDA antagonist MK-801 (dizocilpine maleate, 5-methyl-10, 11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine). Subtle mitochondrial dilatation was identified in a few neurons as early as 15 min postdose (MPD). By 30 MPD, dilatation was more pronounced in mitochondria and also involved the endoplasmic reticulum and perinuclear space. Ribosomal disaggregation and degranulation were also evident by 30 MPD. At all subsequent time points, dilatation of mitochondria and endoplasmic reticulum progressed in severity. Although the relative involvement of mitochondria and endoplasmic reticulum varied, glia were not involved. These ultrastructural data suggest that after treatment with MK-801, mitochondrial dilatation precedes involvement of endoplasmic reticulum in vacuolization of susceptible PC/RS cortical neurons. The early mitochondrial effects identified in this study suggest an initial metabolic insult that rapidly progresses to affect endoplasmic reticulum and ribosomes. This strengthens the relationship between the ability of certain NMDA antagonists to induce energy perturbations and neuronal vacuoles in the same region of the rat cerebral cortex.     

Comparison of the patterns of altered cerebral glucose utilisation produced by competitive and non-competitive NMDA receptor antagonists

Recent studies indicate that competitive and non-competitive NMDA receptor antagonists can be readily distinguished by their effects on local cerebral glucose utilisation (1CGU). In the present study we compare the effects of the novel NMDA antagonist, (+)-1-methyl-1phenyl-1,2,3,4-tetrahydroisoquinoline (FR115427) on 1CGU, comparing its metabolic profile with that of the non-competitive NMDA receptor antagonist, dizocilpine (MK801) and of the competitive NMDA receptor antagonist CGS19755, using the 2-deoxyglucose metabolic mapping approach. Local cerebral glucose utilisation was measured in 80 anatomically discrete regions of the conscious rat brain using [¹⁴C12-deoxyglucose quantitative autoradiography. Studies were initiated 10 min after the administration of FR115427 (0.1–3 mg/kg i.v.;n = 20), dizocilpine (0.03–0.3 mg/kg;n = 15), CGS19755 (1–30 mg/kg;n = 15) or saline (2 ml/kg;n = 5). Dizocilpine produced characteristic alterations in 1CGU with widespread increases in 1CGU in primary olfactory and limbic areas while reducing 1CGU in somatosensory and motor cortex. FR115427 produced a pattern of altered 1CGU which was broadly similar to that elicited by dizocilpine with increases in 1CGU in the pontine nuclei, presubiculum and hippocampus and reductions in somatosensory and motor cortex and within components of the auditory system. However, FR115427 was approximately 30-fold less potent than dizocilpine in this regard. In limbic structures, the effects of FR 115427 were less pronounced than those produced by dizocilpine. Increases in 1CGU of 62–98% were found in retrosplenial, piriform and entorhinal cortex of dizocilpine-treated rats whereas these areas appeared relatively un affected following FR115427 administration. A comparison of the pattern of metabolic response produced by each of these agents was performed by constructing a hierarchy of regional responsiveness using the F statistic: while focal differences in the metabolic profiles of dizocilpine and FR115427 were evident, a plot of the regional F values for dizocilpine and FR115427 revealed a strong overall relationship between the metabolic responses with a Pearson's product moment correlation of 0.78. In contrast, the correlation between the patterns produced by CGS19755 and that for dizocilpine or FR115427 was poor (r = 0.28 and 0.5 respectively).     

Maturation of locomotor and Fos responses to the NMDA antagonists, PCP and MK-801

Antagonists at the N-methyl-D-aspartate (NMDA)-type glutamate receptor, such as phencyclidine (PCP) and dizocilpine (MK-801), are well-known to evoke increases in locomotor activity in adult rats and mice. However, little is known about the effects of NMDA antagonists on locomotor activity as a function of development. The present study examined locomotor responses to PCP or MK-801 in male rats of varying ages and found that prepubertal rats were more sensitive to the locomotor-elevating effects of PCP (1.5 mg/kg and 3. 0 mg/kg, s.c.) than were adults. Locomotor responses to MK-801 (0.1 and 0.2 mg/kg, s.c.) were not dependent on age. The age-dependent response to PCP may be related to developmental events in the motor cortex, since more Fos-immunoreactive neurons were observed in the motor cortex of prepubertal animals after PCP administration relative to adult animals. An opposite pattern of age-dependent Fos responses was observed in the posterior retrosplenial cortex. The results suggest that locomotor responses to NMDA antagonists can be influenced in an age- and drug-dependent manner and that maturational events in the motor cortex may modify responses to PCP.     

Increased expression of zif268 mRNA in rat retrosplenial cortex following administration of phencyclidine

Phencyclidine (PCP) has been shown to cause neurotoxicity in rat retrosplenial cortex following a single administration, although the precise mechanism underlying PCP-induced neurotoxicity is unclear. Using in situ hybridization and immunohistochemistry, we studied the effects of PCP on expression of immediate early gene zif268 mRNA and zif268 protein in the rat brain. High constitutive levels of zif268 mRNA and zif268 immunoreactivity were observed in the brain of control rats. Administration of PCP (12.5, 25 or 50 mg/kg, i.p., 6 h) caused marked induction of zif268 mRNA in the rat retrosplenial cortex, in a dose-dependent manner. However, the basal levels of zif268 mRNA in the other regions of cerebral cortex were decreased by administration of PCP. Emulsion-autoradiographical study suggested that marked expression of zif268 mRNA was observed in the layers III and IV of retrosplenial cortex where the neurotoxicity of PCP was detected. Furthermore, zif268 immunoreactivity in the layer IV of retrosplenial cortex was not changed by administration of PCP (25 mg/kg, i.p., 5 h), but that in the other layers of retrosplenial cortex was reduced by PCP. These results suggest that immediate early gene zif268 may, in part, play a role in the neurotoxicity of NMDA receptor antagonists such as PCP.     

Behavioral changes and expression of heat shock protein hsp-70 mRNA, brain-derived neurotrophic factor mRNA, and cyclooxygenase-2 mRNA in rat brain following seizures induced by systemic administration of kainic acid

Kainic acid-induced seizures in rats represent an established animal model for human temporal lobe epilepsy. However, it is well-known that behavioral responses to the systemic administration of kainic acid are inconsistent between animals. In this study, we examined the relationship between expression of genes, neuropathological damage, and behavioral changes (seizure intensity and body temperature) in rats after systemic administration of kainic acid. The considerable differences in the response to kainic acid-induced seizures were observed in rats after a single administration of kainic acid (12 mg/kg i.p.). There was no detection of the expression of heat shock protein hsp-70 mRNA and HSP-70 protein in brain of vehicle-treated controls and in animals exhibiting weak behavioral changes (stage 1–2). A moderate expression of hsp-70 mRNA was detected throughout all regions (the pyramidal cell layers of CA1–3 and dentate gyrus) of the hippocampus, the basolateral, lateral, central and medial amygdala, the piriform cortex, and the central medial thalamic nucleus of rats that developed moderate seizures (stage 3–4). Marked expression of hsp-70 mRNA was detected in the all regions (cingulate, parietal, somatosensory, insular, entorhinal, piriform cortices) of cerebral cortex and all regions of hippocampus, and the central medial thalamic nucleus of the rats that developed severe seizures (stage 4–5). In addition, marked HSP-70 immunoreactivity was detected in the pyramidal cell layers of CA1 and CA3 regions of hippocampus, all regions (cingulate, parietal, somatosensory, insular, piriform cortices) of cerebral cortex, and the striatum of rats that developed severe seizures (stage 4–5). Furthermore, a marked expression of cyclooxygenase-2 (COX-2) mRNA and brain-derived neurotrophic factor (BDNF) mRNA levels by kainic acid-induced behavioral seizures (stage 3–4 or stage 4–5) was detected in all hippocampal pyramidal cell layers, granule layers of dentate gyrus, piriform cortex, neocortex, and amygdala. The present study suggest that the behavioral changes (seizure intensity and body temperature) and neuropathological damage after systemic administration of kainic acid are inconsistent between animals, and that these behavioral changes (severity of kainic acid-induced limbic seizures) might be correlated with gene expression of hsp-70 mRNA, COX-2 mRNA, and BDNF mRNA in rat brain.     

Effects of sigma ligands on the ability of rimcazole to inhibit PCP hsp70 induction

Phencyclidine (PCP) can result in schizophrenia-like behavior. It binds at the PCP site on the NMDA-receptor calcium channel and at the sigma receptor. PCP also induces the heat shock gene hsp70 in retrosplenial cortex neurons. An antipsychotic drug, rimcazole, inhibits PCP hsp70 induction. Rimcazole binds predominately to sigma-2 sites. It is hypothesized that sigma ligands without antipsychotic properties and with some sigma-2 affinity should partially reverse the effects of rimcazole. (+)-3-PPP, (+)-cyclazocine, and (+)-pentazocine bind predominately to sigma-1 sites. (+)-3-PPP is also a modest sigma-2 ligand. Female Sprague-Dawley rats (200–260 g) were injected intraperitoneally (IP) with (+)-3-PPP (50 mg/kg), rimcazole (60 mg/kg) and, after 5 min, with PCP (40 mg/kg). Brains were sectioned (100 μm) and presence of the hsp70 gene protein product, HSP70, was determined immunocytochemically. (+)-3-PPP significantly (p < 0.05) diminished the ability of rimcazole to inhibit PCP hsp70 induction in the retrosplenial cortex. (+)-Cyclazocine (15mg/kg, IP) and (+)-pentazocine (80mg/kg, IP) given in an analogous manner did not diminished the ability of rimcazole to inhibit PCP hsp70 induction.     

托吡酯对大鼠脑缺血再灌注后神经细胞凋亡和HSP-70表达的影响

目的 了解托吡酯(topiramate)对大鼠局灶性脑缺血再灌注后神经细胞凋亡和热休克蛋白-70(HSP-70) 蛋白表达的影响,探讨托吡酯的神经保护作用机制.方法 用线栓法制备SD大鼠大脑中动脉阻塞再灌注(MCAO)模型, 托吡酯100mg/kg灌胃,qd,应用原位末端标记(TUNEL) 和HSP-70免疫组化染色分别观察大鼠脑缺血再灌注后神经细胞凋亡和HSP-70表达.结果 脑缺血再灌注后2h即出现凋亡细胞,并逐渐增加,2d达高峰,之后逐渐减少.托吡酯干预后,凋亡神经细胞减少,其中再灌注12～48h与对照组比较差异有显著性.脑缺血再灌注后HSP-70的表达于2h逐渐增加,24h达高峰,72h后逐渐降低.托吡酯干预后, 再灌注12h～72h HSP-70表达较对照组显著升高.结论 HSP-70及神经细胞凋亡均参与了脑缺血的病理生理过程,托吡酯具有抑制细胞凋亡和神经保护作用.     

Increased Expression of Cathepsin D in Retrosplenial Cortex of MK-801-Treated Rats

Single administration of a high dose of an uncompetitive NMDA receptor antagonist—dizocilpine maleate (MK-801)—results in transient neuronal vacuolization and cell death in retrosplenial cortex in rodents. In this study expression of cathepsin D (CatD), a major lysosomal aspartic protease, was investigated in brains of female rats treated with 1, 5, or 10 mg/kg of MK-801. Northern blot analysis demonstrated that the CatD mRNA level was moderately increased in retrosplenial cortex 24 h–7 days after the treatment. Concomitantly, increased CatD immunoreactivity was observed, predominantly in the degenerating neurons in layer III of retrosplenial cortex. Neuronal response was spatially distinguished from glial reactivation marked by increased mRNA and protein levels of glial fibrillary acidic protein, as demonstrated by Northern blot and immunohistochemistry in retrosplenial cortex 24 h–7 days after MK-801 treatment. These data suggest that activation of the lysosomal proteolytic system of neurons may play a role in MK-801-evoked neurodegeneration.     

Effects of acute and chronic administration of MK-801 on c-Fos protein expression in mice brain regions implicated in schizophrenia with or without clozapine

This study investigated the effects of acute and chronic administration of the non-competitive NMDA receptor antagonists MK-801 on c-Fos protein expression in different brain regions of mice with or without clozapine. MK-801 (0.6 mg/kg) acute administration produced a significant increase in the expression of c-Fos protein in the layers III–IV of posterior cingulate and retrosplenial (PC/RS) cortex, which was consistent with the previous reports. Moreover, we presented a new finding that MK-801 (0.6 mg/kg) chronic administration for 8 days produced a significant increase of c-Fos protein expression in the PC/RS cortex, prefrontal cortex (PFC) and hypothalamus of mice. Among that, c-Fos protein expression in the PC/RS cortex of mice was most significant. Compared to acute administration, we found that MK-801 chronic administration significantly increased the expression of c-Fos protein in the PC/RS cortex, PFC and hypothalamus. Furthermore, pretreatment of mice with clozapine significantly decreased the expression of c-Fos protein induced by MK-801 acute and chronic administration. These results suggest that c-Fos protein, the marker of neuronal activation, might play an important role in the chronic pathophysiological process of schizophrenic model induced by NMDA receptor antagonist.     

Kainic Acid-induced Heat Shock Protein-70, mRNA and Protein Expression is Inhibited by MK-801 in Certain Rat Brain Regions

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

The nature and time course of neuronal vacuolation induced by the N-methyl-D-aspartate antagonist MK-801

N-Methyl-D-aspartate (NMDA) antagonists cause neuronal vacuolation in the posterior cingulate and retrosplenial cortex of the rat. Because the nature of neuronal pathologic changes due to NMDA antagonists may affect the potential clinical use of this class of drugs, we undertook experiments to define the nature and time course of the vacuolation caused by high-dose (5 mg/kg) MK-801 (dizocilpine, 5-methyl-10, 11-dihydro-5H-dibenzo [a,d]cyclohepten-5,10-imine). Ultrastructural examination revealed the vacuoles to be not a form of hydropic cellular degeneration, but rather a dilatation of several intracellular compartments, chiefly endoplasmic reticulum and mitochondria. Study of the time course of the alterations revealed no light or ultrastructural features of neuronal necrosis in over 1 thousand neurons examined in layers 3 and 4 of the cingulate and retrosplenial cortex, 153 of which were vacuolated. The vacuoles resolved over time by decreasing in magnitude. Oxalate-pyroantimonate methodology revealed no redistribution of cell calcium in either vacuolated or non-vacuolated neurons. At 6 h, when vacuoles were consistently prominent in glutaraldehyde-fixed plastic-embedded tissue, a separate series of experiments was undertaken to vary methods of tissue preparation, and determine conditions under which vacuolation occurs. Frozen sections revealed no vacuoles. Subsequent paraffin embedding of the previously frozen tissue revealed no vacuoles, but vacuoles were seen in paraffin after perfusion fixation. Immersion fixation with brain refrigeration for 12 h prior to fixation revealed no vacuoles. Alcohol fixation also led to no visible vacuoles. We conclude that the vacuolation induced by NMDA antagonists is a reaction to aldehyde fixation of perturbed but living neurons, resulting in artifactual distortion of multiple intracellular compartments.Supported by a grant (MT-9935) from the Medical Research Council of Canada