Effects of antipsychotic drugs on neurotoxicity, expression of fos-like protein and c-fos mRNA in the retrosplenial cortex after administration of dizocilpine

Enhancement in Phospholipase D Activity as a New Proposed Molecular Mechanism of Haloperidol-Induced Neurotoxicity

Membrane phospholipase D (PLD) is associated with numerous neuronal functions, such as axonal growth, synaptogenesis, formation of secretory vesicles, neurodegeneration, and apoptosis. PLD acts mainly on phosphatidylcholine, from which phosphatidic acid (PA) and choline are formed. In turn, PA is a key element of the PLD-dependent secondary messenger system. Changes in PLD activity are associated with the mechanism of action of olanzapine, an atypical antipsychotic. The aim of the present study was to assess the effect of short-term administration of the first-generation antipsychotic drugs haloperidol, chlorpromazine, and fluphenazine on membrane PLD activity in the rat brain. Animals were sacrificed for a time equal to the half-life of the antipsychotic drug in the brain, then the membranes in which PLD activity was determined were isolated from the tissue. The results indicate that only haloperidol in a higher dose increases the activity of phospholipase D. Such a mechanism of action of haloperidol has not been described previously. Induction of PLD activity by haloperidol may be related to its mechanism of cytotoxicity. The finding could justify the use of PLD inhibitors as protective drugs against the cytotoxicity of first-generation antipsychotic drugs like haloperidol.

Clozapine increased c-Fos protein expression in several brain subregions of socially isolated rats

Chronic social stress and/or pharmacological treatments differentially modulate the expression of c-Fos, a marker of neuronal activity, in subregions of the rat brain. Here, we examined the effect of the atypical antipsychotic Clozapine (Clz) (20 mg/kg/day for 3 weeks) on the neuronal activation pattern of c-Fos protein expression in stress-relevant brain subregions of adult male Wistar rats exposed to chronic social isolation (CSIS: 3 weeks), an animal model of depression and schizophrenia, and controls. The protein expression of c-Fos was also used to map neuronal populations in brain subregions activated by CSIS alone. Subregions which showed significantly increased c-Fos protein expression following CSIS included the retrosplenial cortex (RSC), (subregions:RSC granular cortex, c region (RSGc) and dysgranular (RSD)), dentate gyrus, dorsal (DGd), paraventricular thalamic nucleus, posterior part (PVP), lateral (LA)/basolateral (BL) complex of amygdala, caudate putamen (CPu) and accumbens nucleus, shell (AcbSh). Increases in c-Fos protein expression in the RSGc, RSD, DGd, PVP, LA/BL complex of amygdala and striatum (CPu, Acb Core (AcbC) and AcbSh) following Clz treatment in controls were found. Clz applied simultaneously with CSIS modulated neuronal activity in CPu, AcbC and AcbSh subregions compared to CSIS alone, increasing c-Fos protein expression. Furthermore, Clz revealed synergistic effects with CSIS in the CA1d and PVP. These identified neural circuits reflect brain subregions activated following CSIS and/or Clz administration. These data further contribute to the understanding of the effectiveness of Clz in the modulation of brain subregion activation in response to CSIS.

Brain Sub/Region-Specific Effects of Olanzapine on c-Fos Expression of Chronically Socially Isolated Rats

Olanzapine (Olz) is an atypical antipsychotic used to treat depression, anxiety and schizophrenia, which can be caused by chronic psychosocial stress. c-Fos protein expression has been used as an indirect marker of neuronal activity in response to various forms of stress or pharmacological treatments. We examined the effects of a 3-week treatment of Olz (7.5 mg/kg/day) on c-Fos protein expression in stress-relevant brain sub/regions, its relationship with isolation-induced behavioral changes, and potential sites of Olz action on control and male rats exposed to 6 weeks of chronic social isolation (CSIS), an animal model of depression. Olz treatment reversed depression- and anxiety-like behaviors induced by CSIS and suppressed a CSIS-induced increase in the number of c-Fos-positive cells in subregions of the dorsal hippocampus, ventral (v) DG, retrosplenial cortex, and medial prefrontal cortex. In contrast, no change in c-Fos expression was seen in the CA3v, amygdala and thalamic, hypothalamic or striatal subregions in Olz-treated CSIS rats, suggesting different brain sub/regions' susceptibility to Olz. An increased number of c-Fos-positive cells in the CA1v, amygdala and thalamic, hypothalamic and striatal subregions in controls as well as in the CA1v and subregion of the hypothalamus and nucleus accumbens in Olz-treated CSIS rats was found. Results suggest the activation of brain sub/regions following CSIS that may be involved in depressive and anxiety-like behaviors. Olz treatment showed region-specific effects on neuronal activation. Our data contribute to a better understanding of the mechanisms underlying the CSIS response and potential brain targets of Olz in socially isolated rats.

The antipsychotic agent clozapine induces autophagy via the AMPK-ULK1-Beclin1 signaling pathway in the rat frontal cortex

Clozapine, a representative atypical antipsychotic, has superior efficacy compared to other antipsychotic agents and is used for the treatment of severe psychotic disorders. Therefore, studies on its mechanisms of action are important for understanding the mechanisms of therapeutic approaches to psychosis. Adenosine monophosphate-activated protein kinase (AMPK) is a serine-threonine kinase that plays a major role in maintaining metabolic homeostasis. Unc-51-like kinase 1 (ULK1) and Beclin1 are downstream substrates of AMPK and activate the autophagic process. In this study, we examined the effects of clozapine on the AMPK-ULK1-Beclin1 signaling pathway and autophagy in the frontal cortex of the rat. Clozapine (10mg/kg) administration increased the immunoreactivity of p-Thr172-AMPKα in the rat frontal cortex at 1, 2, and 4h after injection, as we previously reported. The immunoreactivity of p-Ser317-ULK1 and p-Ser93-Beclin1 was also increased at 2 and 4h after clozapine injection. At the same time, the immunoreactivity of LC3-II and the Atg5-Atg12 conjugate, which indicate activation of autophagy, was increased. Transmission electron microscopy clearly showed an increase in autophagosome number in the rat frontal cortex at 2h after clozapine injection. To investigate the role of AMPK in clozapine-induced autophagy, the effects of intracerebroventricular injection of compound C, an AMPK inhibitor, were examined. Administration of compound C attenuated the clozapine-induced increase in ULK1 and Beclin1 phosphorylation, as well the protein levels of LC3-II and the Atg5-Atg12 conjugate in the frontal cortex. In summary, the results showed that clozapine activates autophagy through the AMPK-ULK1-Beclin1 signaling pathway in the frontal cortex of the rat.

Antipsychotic treatment modulates glutamate transport and NMDA receptor expression

Schizophrenia patients often suffer from treatment-resistant cognitive and negative symptoms, both of which are influenced by glutamate neurotransmission. Innovative therapeutic strategies such as agonists at metabotropic glutamate receptors or glycin reuptake inhibitors try to modulate the brain's glutamate network. Interactions of amino acids with monoamines have been described on several levels, and first- and second-generation antipsychotic agents (FGAs, SGAs) are known to exert modulatory effects on the glutamatergic system. This review summarizes the current knowledge on effects of FGAs and SGAs on glutamate transport and receptor expression derived from pharmacological studies. Such studies serve as a control for molecular findings in schizophrenia brain tissue and are clinically relevant. Moreover, they may validate animal models for psychosis, foster basic research on antipsychotic substances and finally lead to a better understanding of how monoaminergic and amino acid neurotransmissions are intertwined. In the light of these results, important differences dependent on antipsychotic substances, dosage and duration of treatment became obvious. While some post-mortem findings might be confounded with multifold drug effects, others are unlikely to be influenced by antipsychotic treatment and could represent important markers of schizophrenia pathophysiology. In similarity to the convergence of toxic and psychotomimetic effects of dopaminergic, serotonergic and anti-glutamatergic substances, the therapeutic mechanisms of SGAs might merge on a yet to be defined molecular level. In particular, serotonergic effects of SGAs, such as an agonism at 5HT1A receptors, represent important targets for further clinical research.

Neurobehavioral effects, c-Fos/Jun expression and tissue distribution in rat offspring prenatally co-exposed to MeHg and PFOA: PFOA impairs Hg retention

Exposure to methylmercury (MeHg) and perfluorooctanoic acid (PFOA) can occur simultaneously as both contaminants are found in the same food sources, especially fish, seafood, marine mammals and milk. The aim of this study was to assess the effects of exposure to MeHg (10 μg mL(-1) in drinking water) and PFOA (10 μg mL(-1) in drinking water) from gestational day 1 to postnatal day (PND) 21, alone and in combination, on neurobehavioral development and the expression of c-Fos/Jun in different brain regions in the offspring. Our findings showed that exposure to MeHg alone, and exposure to MeHg combined with PFOA significantly induced cliff avoidance reflexes and negative geotaxis reflexes. And these effects appeared to be greater following exposure to MeHg alone. MeHg and/or PFOA exposure did not significantly impair motor coordination functions, or cause significant changes in c-Fos expression in the hippocampus and cerebellum, and spatial learning tests were similar to those in the controls, thus it was impossible to determine whether combined exposure to MeHg and PFOA had any additional effects on both hippocampus and cerebellum regions. However, a significant increase in the frequency of line crossing was observed in rats treated with MeHg or PFOA alone, and there were no significant differences between the MeHg+PFOA-treated group and the controls, suggesting that PFOA was antagonistic to MeHg toxicity in the locomotor activity test. Co-exposure to MeHg and PFOA decreased all tissue Hg concentrations in pups compared to the group exposed to MeHg only, suggesting that PFOA impaired Hg retention in different tissues.

The role of endogenous neurotensin in psychostimulant-induced disruption of prepulse inhibition and locomotion

The neuropeptide neurotensin (NT) is closely associated with dopaminergic and glutamatergic systems in the rat brain. Central injection of NT into the nucleus accumbens (NAcc) or peripheral administration of NT receptor agonists, reduces many of the behavioral effects of psychostimulants. However, the role of endogenous NT in the behavioral effects of psychostimulants (e.g. DA agonists and NMDA receptor antagonists) remains unclear. Using a NTR antagonist, SR142948A, the current studies were designed to examine the role of endogenous NT in DA receptor agonist- and NMDA receptor antagonist-induced disruption of prepulse inhibition of the acoustic startle response (PPI), locomotor hyperactivity and brain-region specific c-fos mRNA expression. Adult male rats received a single i.p. injection of SR142948A or vehicle followed by D-amphetamine, apomorphine or dizocilpine challenge. SR142948A had no effect on baseline PPI, but dose-dependently attenuated d-amphetamine- and dizocilpine-induced PPI disruption and enhanced apomorphine-induced PPI disruption. SR142948A did not significantly affect either baseline locomotor activity or stimulant-induced hyperlocomotion. Systemic SR142948A administration prevented c-fos mRNA induction in mesolimbic terminal fields (prefrontal cortex, lateral septum, NAcc, ventral subiculum) induced by all three psychostimulants implicating the VTA as the site for NT modulation of stimulant-induced PPI disruption. Further characterization of the NT system may be valuable to find clinical useful compounds for schizophrenia and drug addiction.

Different antipsychotics elicit different effects on magnocellular oxytocinergic and vasopressinergic neurons as revealed by Fos immunohistochemistry

Acute administration of antipsychotics elicits regionally distinct patterns of Fos expression in the rat brain. Stimulation of oxytocin (OXY) and vasopressin (AVP) release in the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei indicates that antipsychotics may play a role in autonomic, neuroendocrine, and behavioral processes. This study was focused to reveal the responsiveness of hypothalamic OXY- and AVP- producing magnocellular neurons, in terms of quantitative and topographical distinctions, to antipsychotics displaying different pharmacological profiles. Naive male Wistar rats were injected intraperitoneally with haloperidol (1 mg/kg), clozapine (30 mg/kg), olanzapine (30 mg/kg), risperidone (2mg/kg), and vehicle (5% chremophor) and were sacrificed 60 min later by a fixative. Fos, Fos/OXY, and Fos/AVP labelings were visualized by immunohistochemistry in the SON, 5 accessory (ACS) cell groups, and 4 distinct PVN subdivisions using a computerized light microscope. Most apparent activation of single Fos, Fos/OXY, and Fos/AVP cells was induced by clozapine and olanzapine; effects of risperidone and haloperidol were substantially lower; no colocalizations were revealed in naive or vehicle treated control rats. The data indicate the existence of a substantial diversity in the stimulatory effect of the selected antipsychotics on quantity of Fos, Fos/OXY, and Fos/AVP immunostainings with the preferential action of the atypicals clozapine over olanzapine and little effects of risperidone and haloperidol. Variabilities in Fos distribution in the PVN, SON, and ACS induced by antipsychotics may be helpful to understand more precisely the extent of their extra-forebrain actions with possible presumption of their functional impact and side effect consequences.

Assessing noxious effects of dietary exposure to methylmercury, PCBs and Se coexisting in environmentally contaminated rice in male mice

Polychlorinated biphenyls and methylmercury are two of the most ubiquitous environmental contaminants in Guizhou province. Rice is eaten with almost every meal and provides more calories than any single food in Guizhou province. The estimated tolerable daily intake of total mercury, MeHg, Se and PCBs from Guizhou contaminated rice by Chinese people showed that MeHg and/or PCBs exceeded the corresponding limits. The aim of this study was to characterize the effects of exposure to environmental contaminated rice on neurobehavioral development and neurobiological disruptions in mice. Animals were treated from postnatal day (PND) 22 to 91. At PND 26-91 days of age, mice were tested for neurobehavioural development and neurochemical level changes. We showed that dietary exposure to environmentally contaminated rice gave rise to different changes in antioxidants. Reduced superoxide dismutase (SOD) activity and excess increased nitric oxide (NO) indicated aggravation of oxidative status after long-term dietary intake of Hg and PCBs. Neurobehavioral derangement in the central nervous system and significant delay in the Morris water maze test response on PND 91 are correlated with the increased of c-fos/c-jun expression levels in the cerebral cortex. These results suggest that MeHg neurotoxicity might be a greater hazard than that associated with PCB, but PCB may augment the neurobehavioral deficits caused by increased levels of mercury exposure. The simultaneous intake of selenium might have a protective effect on Hg accumulation in the body, and vitamin C might protect mice against the toxic effects of PCBs. However, the protective role of Se and vitamin C is very limited for multiple-agent pollution. Immediately early genes in the brain response to contaminated rice might be dependent on interaction among NO, NO synthase (NOS), SOD and reduced glutathione (GSH). We should be alert to mental health problems in human beings when any kind of Hg- and PCB-polluted food is consumed.

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.

Antipsychotic drugs: comparison in animal models of efficacy, neurotransmitter regulation, and neuroprotection

Various lines of evidence indicate the presence of progressive pathophysiological processes occurring within the brains of patients with schizophrenia. By modulating chemical neurotransmission, antipsychotic drugs may influence a variety of functions regulating neuronal resilience and viability and have the potential for neuroprotection. This article reviews the current literature describing preclinical and clinical studies that evaluate the efficacy of antipsychotic drugs, their mechanism of action and the potential of first- and second-generation antipsychotic drugs to exert effects on cellular processes that may be neuroprotective in schizophrenia. The evidence to date suggests that although all antipsychotic drugs have the ability to reduce psychotic symptoms via D(2) receptor antagonism, some antipsychotics may differ in other pharmacological properties and their capacities to mitigate and possibly reverse cellular processes that may underlie the pathophysiology of schizophrenia.

Risperidone attenuates MK-801-induced hyperlocomotion in mice via the blockade of serotonin 5-HT2A/2C receptors

Glutamate N-methyl-D-aspartate (NMDA) receptor antagonists, like phencyclidine (PCP), elicit schizophrenia-like symptoms in humans and behavioral abnormalities in animals, such as hyperactivity. We investigated the effect of the atypical antipsychotic risperidone on hyperlocomotion produced in mice by 5R,10S-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]-cyclohepten-5,10-imine hydrogen maleate (MK-801), an NMDA receptor antagonist. MK-801 (0.125, 0.25, 0.50 mg/kg) dose-dependently increased the total distance traveled in an open field during a 90 min period in mice. The increase in MK-801 (0.25 mg/kg)-induced total distance traveled was attenuated by pretreatment with risperidone at doses that alone had no effect on spontaneous locomotor activity. Furthermore, (+/-)-1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI), a serotonin 5-HT(2A/2C) receptor agonist, at the doses that failed to change spontaneous locomotor activity or hyperlocomotion induced by MK-801, reversed the attenuation by risperidone. The serotonin 5-HT(2A/2C) receptor antagonist, ritanserin, enhanced the inhibitory effect of risperidone. These findings indicate that risperidone attenuates MK-801-induced hyperlocomotion in mice by blocking serotonin 5-HT(2A/2C) receptors.

Suppressive effect of clozapine but not haloperidol on the increases of neuropeptide-degrading enzymes and glial cells in MK-801-treated rat brain regions

MK-801, a noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist, produces neurotoxicity in adult rodent brain, and causes schizophrenia-like psychosis and cognitive dysfunction. Since neuropeptides and neuropeptide-degrading enzymes play important roles in cognitive function, we examined whether or not MK-801-induced schizophrenia-like psychosis is co-related with the changes of these enzymes in rat brain regions. In the present study, we investigated the effect of systemic treatment with MK-801 (0.5mg/kg) on neuropeptide-degrading enzymes, prolyl oligopeptidase (POP) and thimet oligopeptidase (EP 24.15), and glial marker proteins GFAP and CD11b in rat brain regions. The levels of POP and EP 24.15 activities increased significantly three days after treatment with MK-801 in the posterior cingulate/retrosplenial cortices (PC/RSC). Since atypical neuroleptic clozapine but not typical neuroleptic haloperidol prevents the MK-801-induced schizophrenia-like symptoms, we further examined the pretreated effects of the neuroleptics. Clozapine, but not haloperidol, significantly attenuated MK-801-induced changes in the levels of the neuropeptide-degrading enzymes. Immunohistochemical studies on GFAP and CD11b showed the increase in the PC/RSC of MK-801-treated rat brain and the pretreatment with clozapine suppressed these changes. Double immunostain experiments of EP 24.15 and GFAP antibodies demonstrated some co-localization of the neuropeptidase with astrocytes. The present findings suggest that change of neuropeptidases in the brain is in part correlated with changes of glial cells, and may play an important role in the control of schizophrenia-like psychotic disorders.

Clozapine but not haloperidol suppresses the changes in the levels of neuropeptides in MK-801-treated rat brain regions

Noncompetitive NMDA receptor antagonist (+)MK-801 is known to induce neurotoxicity and schizophrenia-like symptomatology where atypical neuroleptic clozapine is effective in contrast to typical neuroleptic, haloperidol. Although neuropeptides are implicated in memory and cognition, their roles in schizophrenia are not well understood. In the present study, we therefore examined the possible roles of neuropeptides, cholecystokinin (CCK) and somatostatin (SS) in the posterior cingulate/retrosplenial cortices (PC/RSC), frontal cortex, and hippocampus of a MK-801-induced schizophrenia-like model rat brain. This study further investigated the pretreated effect of atypical versus typical neuroleptics on the peptidergic system. SS mRNA and peptide levels significantly decreased in the PC/RSC and hippocampus but not in the frontal cortex 3 days after 0.5 mg/kg MK-801 treatment whereas CCK mRNA and peptide levels significantly decreased in all of the brain regions examined. Pretreatment with clozapine but not haloperidol completely recovered the changes in both mRNA and peptide levels of SS and CCK in those brain regions. These data suggest that peptidergic system in the brain presumably plays an important role in the control of negative schizophrenia.

Clinically approved heterocyclics act on a mitochondrial target and reduce stroke-induced pathology

Substantial evidence indicates that mitochondria are a major checkpoint in several pathways leading to neuronal cell death, but discerning critical propagation stages from downstream consequences has been difficult. The mitochondrial permeability transition (mPT) may be critical in stroke-related injury. To address this hypothesis, identify potential therapeutics, and screen for new uses for established drugs with known toxicity, 1,040 FDA-approved drugs and other bioactive compounds were tested as potential mPT inhibitors. We report the identification of 28 structurally related drugs, including tricyclic antidepressants and antipsychotics, capable of delaying the mPT. Clinically achievable doses of one drug in this general structural class that inhibits mPT, promethazine, were protective in both in vitro and mouse models of stroke. Specifically, promethazine protected primary neuronal cultures subjected to oxygen-glucose deprivation and reduced infarct size and neurological impairment in mice subjected to middle cerebral artery occlusion/reperfusion. These results, in conjunction with new insights provided to older studies, (a) suggest a class of safe, tolerable drugs for stroke and neurodegeneration; (b) provide new tools for understanding mitochondrial roles in neuronal cell death; (c) demonstrate the clinical/experimental value of screening collections of bioactive compounds enriched in clinically available agents; and (d) provide discovery-based evidence that mPT is an essential, causative event in stroke-related injury.

Adenosine A1 receptor agonists block the neuropathological changes in rat retrosplenial cortex after administration of the NMDA receptor antagonist dizocilpine

Noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine ((+)-MK-801) is known to induce neurotoxicity in rat retrosplenial cortex after systemic administration. The present study was undertaken to examine the effects of adenosine A(1) receptor agonists on the neurotoxicity in rat retrosplenial cortex after administration of dizocilpine. Pretreatment with adenosine A(1) receptor agonists, 2-chloro-N(6)-cyclopentyladenosine (CCPA) (0.1, 0.3, 1, or 3 mg/kg, intraperitoneally (i.p.)), or N(6)-cyclopentyladenosine (CPA) (1, 3, or 10 mg/kg, i.p.), attenuated neurotoxicity by dizocilpine (0.5 mg/kg, i.p), in a dose-dependent manner. Coadministration with adenosine A(1) receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (DPCPX; 3 mg/kg, i.p.) significantly blocked the protective effects of CCPA for dizocilpine-induced neurotoxicity. Furthermore, pretreatment with CCPA (3 mg/kg) attenuated significantly the dizocilpine-induced expression of HSP-70 protein, which is known as a sensitive marker of reversible neuronal damage, and coadministration with DPCPX (3 mg/kg) blocked the inhibitory effects of CCPA for marked expression of HSP-70 protein by administration of dizocilpine. Moreover, pretreatment with CCPA (3 mg/kg, i.p.) significantly suppressed the increase of extracellular acetylcholine (ACh) levels in the retrosplenial cortex by administration of dizocilpine (0.5 mg/kg). In contrast, local perfusion of CCPA (1 microM) into the retrosplenial cortex via the dialysis probe did not alter the ACh levels by administration of dizocilpine (0.5 mg/kg), suggesting that the locus of action of CCPA is not in the retrosplenial cortex. These findings suggest that adenosine A(1) receptors agonists could protect against neuropathological changes in rat retrosplenial cortex after administration of the NMDA receptor antagonist dizocilpine.

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.

Bilateral lesions of the entorhinal cortex differentially modify haloperidol- and olanzapine-induced c-fos mRNA expression in the rat forebrain

Lesions of the entorhinal cortex are now an accepted model for mimicking some of the neuropathological aspects of schizophrenia, since evidence has accumulated for the presence of cytoarchitectonic abnormalities within this cortex in schizophrenic patients. The present study was undertaken to address the functional consequences of bilateral entorhinal cortex lesions on antipsychotic-induced c-fos expression. After a 15-day recovery period, the effect of a typical antipsychotic, haloperidol (1 mg/kg), on c-fos mRNA expression was compared with that of an atypical one, olanzapine (10 mg/kg), in both sham-lesioned and entorhinal cortex-lesioned rats. In sham-lesioned rats, both haloperidol and olanzapine induced c-fos expression in the caudal cingulate cortex, dorsomedial and dorsolateral caudate-putamen, nucleus accumbens core and shell and lateral septum. In addition, olanzapine, but not haloperidol, increased c-fos expression within the central amygdala. In entorhinal cortex-lesioned rats, haloperidol-induced c-fos expression was markedly reduced in most areas. In contrast, the olanzapine-induced c-fos expression was not altered in the nucleus accumbens shell and lateral septum of the lesioned rats. These findings reveal that entorhinal cortex lesions affect c-fos expression in a compound- and regional-dependent manner. Our results further emphasize the importance of the exploration of the mechanisms of action of antipsychotic drugs in the context of an associated cortical pathology.

Fos induction in the rat deep cerebellar and vestibular nuclei following central administration of colchicine: a qualitative and quantitative time-course study

The present study was conducted to demonstrate Fos expression at four levels (anterior, prefastigial, postfastigial, posterior) of the cerebellar-vestibular nuclear complex in rats exposed to 1, 6, 24, and 48h of colchicine treatment using a light microscopic avidin biotin peroxidase (ABC) immunohistochemistry. Intracerebroventricular administration of colchicine (60microg per 10microl saline) elicited a continuous increase in the number of Fos-positive cells in the main cerebellar (fastigial, interpositus, dentatus) and vestibular (superior, medial, lateral, spinal, Y) nuclei. One and six hours after colchicine treatment, intensive Fos labeling was observed only in the pyriform cortex and the hypothalamic paraventricular nucleus, respectively, and there was no Fos immunolabeling in any of the cerebellar or vestibular structures investigated. On the other hand, moderate number of Fos-positive cells was visible in each of the cerebellar and vestibular nuclei 24h after colchicine treatment. Exposure of the animals to 48h of colchicine treatment induced an additional, more than 50%, rise in the accumulation of Fos-positive profiles in almost all the cerebellar and vestibular nuclei. In addition, at this time-point, a characteristic pattern of Fos distribution appeared almost in all of the cerebellar and vestibular nuclei, however, the numerical incidence of Fos-positive profiles in paired structures along the neuroaxis was bilaterally symmetric. The present data demonstrate for the first time that the central administration of colchicine causes a persistent and, in comparison with other brain areas, time-delayed activation of certain population of neurons in both cerebellar and vestibular nuclei. We assume that the delayed Fos activation in these structures indicate that the cerebellar and vestibular nuclei are not the primary targets of the central effect of colchicine and their activation seems to be rather a result of a postponed functional consequences of the central action of colchicine probably related to the coordination of motor performance.

Protective effect of the antipsychotic drug zotepine on dizocilpine-induced neuropathological changes in rat retrosplenial cortex

An atypical antipsychotic drug, zotepine, which is pharmacologically and clinically related to clozapine, has unique therapeutic effects on patients with schizophrenia. It has been demonstrated that clozapine blocks neurotoxicity in the rat retrosplenial cortex induced by administration of the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine ((+)-MK-801). We examined whether or not zotepine has the ability to block neurotoxicity in the rat retrosplenial cortex induced by administration of dizocilpine. Female Sprague-Dawley rats were injected intraperitoneally (i.p.) with vehicle (1 mg/kg), zotepine (5, 10 or 20 mg/kg) or clozapine (20 mg/kg). Fifteen minutes later, animals were injected intraperitoneally (i.p.) with vehicle (1 ml/kg) or dizocilpine (0.5 mg/kg). Neuropathological changes (neuronal vacuolization) were assessed 4 h after administration of dizocilpine. Immunohistochemical analysis of heat shock protein HSP-70, a marker of reversible neuronal injury, was performed 24 h after administration of dizocilpine. The pretreatment with zotepine (5, 10 or 20 mg/kg) significantly decreased the number of vacuolized neurons in the rat retrosplenial cortex 4 h after the administration of dizocilpine (0.5 mg/kg), in a dose-dependent manner. The potency of zotepine (20 mg/kg) for dizocilpine-induced neurotoxicity was similar to that of clozapine (20 mg/kg). Furthermore, similar to the case with clozapine (20 mg/kg, i.p.), zotepine (20 mg/kg, i.p.) significantly attenuated the expression of HSP-70 in the rat retrosplenial cortex induced by dizocilpine (0.5 mg/kg, i.p.). The present study suggests that the neuroprotective effects of zotepine- on dizocilpine-induced neurotoxicity are equipotent to those of clozapine. Based on the NMDA receptor hypofunction hypothesis of schizophrenia, the efficacy of zotepine in this study may partly contribute to the unique therapeutic effects of zotepine in patients with schizophrenia.

Effects of MK-801 and electroconvulsive shock on c-Fos expression in the rat hippocampus and frontal cortex

Both the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 and electroconvulsive shock (ECS) have been reported to induce c-Fos in rat brain. However, the former has anticonvulsant and psychotomimetic effects and the latter has proconvulsant and antipsychotic effects. To understand the mode of action of these treatments, the authors examined the effect of MK-801 and the interaction between MK-801 and ECS on the induction of c-Fos in the rat hippocampus and frontal cortex. MK-801 induced c-Fos in these brain regions in a nonlinear dose-response relationship. Maximum effect was achieved with 1-2 mg/kg of MK-801. The level of c-Fos paralleled animal hyperkinetic behavior, suggesting the role of c-Fos in the induced psychotomimetic behaviors. Pretreatment with MK-801 dose-dependently attenuated both the seizures and c-Fos expression by ECS. However, at an MK-801 pretreatment dose of 8 mg/kg, which completely blocked ECS-induced seizure, the induction of c-Fos was not completely blocked, suggesting non-NMDA mediated pathways of the induction of c-Fos by ECS.