Phencyclidine (PCP) and dizocilpine (MK801) exert time-dependent effects on the expression of immediate early genes in rat brain

Towards Novel Treatments for Schizophrenia: Molecular and Behavioural Signatures of the Psychotropic Agent SEP-363856

Schizophrenia is a complex psychopathology whose treatment is still challenging. Given the limitations of existing antipsychotics, there is urgent need for novel drugs with fewer side effects. SEP-363856 (SEP-856) is a novel psychotropic agent currently under phase III clinical investigation for schizophrenia treatment. In this study, we investigated the ability of an acute oral SEP-856 administration to modulate the functional activity of specific brain regions at basal levels and under glutamatergic or dopaminergic-perturbed conditions in adult rats. We found that immediate-early genes (IEGs) expression was strongly upregulated in the prefrontal cortex and, to a less extent, in the ventral hippocampus, suggesting an activation of these regions. Furthermore, SEP-856 was effective in preventing the hyperactivity induced by an acute injection of phencyclidine (PCP), but not of d-amphetamine (AMPH). The compound effectively normalized the PCP-induced increase in IEGs expression in the PFC at all doses tested, whereas only the highest dose determined the major modulations on AMPH-induced changes. Lastly, SEP-856 acute administration corrected the cognitive deficits produced by subchronic PCP administration. Taken together, our data provide further insights on SEP-856, suggesting that modulation of the PFC may represent an important mechanism for the functional and behavioural activity of this novel compound.

GluN2A NMDA Receptor Enhancement Improves Brain Oscillations, Synchrony, and Cognitive Functions in Dravet Syndrome and Alzheimer's Disease Models

NMDA receptors (NMDARs) play subunit-specific roles in synaptic function and are implicated in neuropsychiatric and neurodegenerative disorders. However, the in vivo consequences and therapeutic potential of pharmacologically enhancing NMDAR function via allosteric modulation are largely un-known. We examine the in vivo effects of GNE-0723, a positive allosteric modulator of GluN2A-subunit-containing NMDARs, on brain network and cognitive functions in mouse models of Dravet syndrome (DS) and Alzheimer’s disease (AD). GNE-0723 use dependently potentiates synaptic NMDA receptor currents and reduces brain oscillation power with a predominant effect on low-frequency (12–20 Hz) oscillations. Interestingly, DS and AD mouse models display aberrant low-frequency oscillatory power that is tightly correlated with network hypersynchrony. GNE-0723 treatment reduces aberrant low-frequency oscillations and epileptiform discharges and improves cognitive functions in DS and AD mouse models. GluN2A-subunit-containing NMDAR enhancers may have therapeutic benefits in brain disorders with network hypersynchrony and cognitive impairments.

Hanson et al. examine the therapeutic effects of enhancing GluN2A-subunit-containing NMDAR function in Dravet syndrome and Alzheimer’s disease mice. GNE-0723 treatment reduces aberrant low-frequency oscillations and epileptiform discharges and improves cognitive functions in both disease models. GluN2A NMDAR enhancers may benefit brain disorders with network hypersynchrony and cognitive impairments.

Acute phencyclidine administration induces c-Fos-immunoreactivity in interneurons in cortical and subcortical regions

Dysfunction of N-Methyl-d-aspartate receptors (NMDARs) is believed to underlie some of the symptoms in schizophrenia, and non-competitive NMDAR antagonists (including phencyclidine (PCP)) are widely used as pharmacological schizophrenia models. Furthermore, mounting evidence suggests that impaired γ-aminobutyric acid (GABA) neurotransmission contributes to the cognitive deficits in schizophrenia. Thus alterations in GABAergic interneurons have been observed in schizophrenia patients and animal models. Acute systemic administration of PCP increases levels of c-Fos in several cortical and subcortical areas, but whether such induction occurs in specific populations of GABAergic interneuron subtypes still remains to be established. We performed an immunohistochemical analysis of the PCP-induced c-Fos-immunoreactivity (IR) in parvalbumin (PV) and calbindin (CB) interneuron subtypes in the cortex and thalamus of rats. A single dose of PCP (10mg/kg, s.c.) significantly increased total number of c-Fos-IR in: (1) the prelimbic, infralimbic, anterior cingulate, ventrolateral orbital, motor, somatosensory and retrosplenial cortices as well as the nucleus accumbens (NAc), field CA1 of the hippocampus (CA1) field of hippocampus and mediodorsal thalamus (MD); (2) PV-IR cells in the ventrolateral orbitofrontal and retrosplenial cortices and CA1 field of hippocampus; and (3) CB-IR cells in the motor cortex. Overall, our data indicate that PCP activates a wide range of cortical and subcortical brain regions and that a substantial part of this activation is present in GABAergic interneurons in certain regions. This suggests that the psychotomimetic effect of PCP may be mediated via GABAergic interneurons.

Global quantitative analysis of phosphorylation underlying phencyclidine signaling and sensorimotor gating in the prefrontal cortex

Prepulse inhibition (PPI) is an example of sensorimotor gating and deficits in PPI have been demonstrated in schizophrenia patients. Phencyclidine (PCP) suppression of PPI in animals has been studied to elucidate the pathological elements of schizophrenia. However, the molecular mechanisms underlying PCP treatment or PPI in the brain are still poorly understood. In this study, quantitative phosphoproteomic analysis was performed on the prefrontal cortex from rats that were subjected to PPI after being systemically injected with PCP or saline. PCP downregulated phosphorylation events were significantly enriched in proteins associated with long-term potentiation (LTP). Importantly, this data set identifies functionally novel phosphorylation sites on known LTP-associated signaling molecules. In addition, mutagenesis of a significantly altered phosphorylation site on xCT (SLC7A11), the light chain of system xc-, the cystine/glutamate antiporter, suggests that PCP also regulates the activity of this protein. Finally, new insights were also derived on PPI signaling independent of PCP treatment. This is the first quantitative phosphorylation proteomic analysis providing new molecular insights into sensorimotor gating.

Perspectives on zebrafish models of hallucinogenic drugs and related psychotropic compounds

Among different classes of psychotropic drugs, hallucinogenic agents exert one of the most prominent effects on human and animal behaviors, markedly altering sensory, motor, affective, and cognitive responses. The growing clinical and preclinical interest in psychedelic, dissociative, and deliriant hallucinogens necessitates novel translational, sensitive, and high-throughput in vivo models and screens. Primate and rodent models have been traditionally used to study cellular mechanisms and neural circuits of hallucinogenic drugs' action. The utility of zebrafish ( Danio rerio ) in neuroscience research is rapidly growing due to their high physiological and genetic homology to humans, ease of genetic manipulation, robust behaviors, and cost effectiveness. Possessing a fully characterized genome, both adult and larval zebrafish are currently widely used for in vivo screening of various psychotropic compounds, including hallucinogens and related drugs. Recognizing the growing importance of hallucinogens in biological psychiatry, here we discuss hallucinogenic-induced phenotypes in zebrafish and evaluate their potential as efficient preclinical models of drug-induced states in humans.

Studies in schizophrenia: pathophysiology and treatment

Studies on the pathophysiology of schizophrenia have implicated the limbic cortex, using postmortem, structural, and functional data, especially in the hippocampus (HC) and the anterior cingulate cortex (ACC). We have made contributions to the literature consistent with this idea: first, we describe a positive significant correlation between psychotic symptoms in schizophrenia and neuronal activity in the ACC and HC, suggesting the involvement of limbic cortex in the mediation of symptoms in schizophrenia. Second, in the ACC and the anterior HC (but not in the posterior HC), regional cerebral blood flow (rCBF) is abnormal (ie, reduced in the ACC and elevated in the HC) in schizophrenia. Third, the relationship of rCBF to task difficulty in the ACC is altered in schizophrenia, suggesting a failure of participation of the ACC in effortful tasks. Lastly, connectivity between the ACC and HC during the performance of an auditory discrimination task is also lacking, suggesting that cognitive performance in schizophrenia lacks a functional limbic contribution. On the basis of these changes, we studied the effects of antipsychotic drugs in these abnormal areas in persons with schizophrenia. Both first- and second-generation antipsychotics produce functional alterations in these limbic cortical areas, in the direction of normals, putatively acting through the brain's own cortical-subcortical circuits.

Neurochemical and molecular characterization of ketamine-induced experimental psychosis model in mice

Ketamine, an NMDA receptor antagonist has been shown to induce aberrant behaviour phenotypes in rodents, some of which are known to simulate the behaviour abnormalities observed in patients suffering from schizophrenia. Thus, developing ketamine-induced animal models became an important tool of choice to study the mechanistic details of some critical symptoms associated with schizophrenia. In this study, our goal was to characterize and correlate the ketamine-induced changes in the behavioural phenotypes to the changes in neurochemical and molecular profile(s) in the brain tissues implicated in the pathophysiology of schizophrenia. We studied the effects of ketamine in mice using 'acute' and 'chronic' treatment regimens along with the 'drug withdrawal' effects on their biochemical and molecular parameters in the pre-frontal cortex, hippocampus, and striatum. Our results demonstrated that the acute and chronic ketamine administration, differentially and site specifically, modulated the levels of acetylcholine, dopamine, serotonin and noradrenaline. In addition, the chronic ketamine doses dramatically suppressed the levels of glycine among some of the amino acids examined and induced alternations in gene expression of the key neurotransmitter receptor systems, including some members of the dopamine and the serotonin receptor families. The acute and chronic ketamine treatment induced "signature" neurochemical and gene-expression patterns that are implicated in the pathophysiology of schizophrenia. Our analyses tend to support the "chronic ketamine" mice model for experimental psychosis as a tool for deeper investigation of the mechanistic paradigm associated with the schizophrenia spectrum disorder and for screening next-generation antipsychotic drugs.

Cholinergic denervation attenuates phencyclidine-induced c-fos responses in rat cortical neurons

The cortical cholinergic innervation, which is important for memory and cognition, has been implicated in schizophrenia. To experimentally analyze such a possible role of the cholinergic system, we have used the dissociative drug phencyclidine (PCP), known to produce schizophrenia-like psychosis in humans, to model aspects of schizophrenia in rats. We previously showed that induced cortical cholinergic hypofunction leads to enhanced PCP-induced locomotor activity and attenuated social interaction. After PCP, rats lacking cortical cholinergic innervation also show impaired declarative memory. To directly study the role of the basalo-cortical cholinergic projections for PCP-induced neural activation in different cortical areas, we have now monitored the rapid (30 and 60 min) effects of low doses of PCP (2 and 3mg/kg) on neural activation as reflected by transcriptional activation of c-fos in cortical areas, using quantitative in situ hybridization. We find an almost pan-cortical neural induction of c-fos mRNA with doses of PCP low enough not to alter levels of either BDNF or Nogo receptor mRNA levels. Specific unilateral lesioning of the uncrossed cholinergic projections to the cortical mantle by 192-IgG-saporin immunotoxin delivery to nc basalis (NBM) caused a striking ipsilateral decrease of the PCP-induced cortical c-fos mRNA induction, restricted to areas which had become effectively denervated. Because PCP at low doses is unlikely to directly influence cortical neurons, we suggest that it acts by activation of the cholinergic input, which in turn leads to cortical c-fos mRNA increases. Our results are compatible with a role for the cholinergic system in symptoms of schizophrenia, by showing that the basalo-cortical cholinergic projections are needed in order for PCP to have full activating effects on cortical neurons.

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.

Dopamine pathology in schizophrenia: analysis of total and phosphorylated tyrosine hydroxylase in the substantia nigra

INTRODUCTION

Despite the importance of dopamine neurotransmission in schizophrenia, very few studies have addressed anomalies in the mesencephalic dopaminergic neurons of the substantia nigra/ventral tegmental area (SN/VTA). Tyrosine hydroxylase (TH) is the rate-limiting enzyme for the production of dopamine, and a possible contributor to the anomalies in the dopaminergic neurotransmission observed in schizophrenia.

OBJECTIVES

In this study, we had three objectives: (1) Compare TH expression (mRNA and protein) in the SN/VTA of schizophrenia and control postmortem samples. (2) Assess the effect of antipsychotic medications on the expression of TH in the SN/VTA. (3) Examine possible regional differences in TH expression anomalies within the SN/VTA.

METHODS

To achieve these objectives three independent studies were conducted: (1) A pilot study to compare TH mRNA and TH protein levels in the SN/VTA of postmortem samples from schizophrenia and controls. (2) A chronic treatment study was performed in rodents to assess the effect of antipsychotic medications in TH protein levels in the SN/VTA. (3) A second postmortem study was performed to assess TH and phosphorylated TH protein levels in two types of samples: schizophrenia and control samples containing the entire rostro-caudal extent of the SN/VTA, and schizophrenia and control samples containing only mid-caudal regions of the SN/VTA.

RESULTS AND CONCLUSION

Our studies showed impairment in the dopaminergic system in schizophrenia that could be mainly (or exclusively) located in the rostral region of the SN/VTA. Our studies also showed that TH protein levels were significantly abnormal in schizophrenia, while mRNA expression levels were not affected, indicating that TH pathology in this region may occur posttranscriptionally. Lastly, our antipsychotic animal treatment study showed that TH protein levels were not significantly affected by antipsychotic treatment, indicating that these anomalies are an intrinsic pathology rather than a treatment effect.

Glutamate and nicotinic receptor interactions in working memory: importance for the cognitive impairment of schizophrenia

This article reaches across disciplines to correlate results in molecular, cellular, behavioral, and clinical research to develop a more complete picture of how working memory (WM) functions. It identifies a new idea that deserves further investigation. NMDA glutamate receptors (NMDAR) are critical for memory function. NMDAR inhibition effectively reproduces principal manifestations of schizophrenia (SP), such as WM impairment and GABAergic deficit (mainly reduction of glutamic acid decarboxylase 67 (GAD67) and parvalbumin (PV) content). Nicotine and selective α7 nicotinic acetylcholine receptor (nAChR) agonists reduce WM impairments in patients with SP and reverse WM deficits in animals treated with NMDAR antagonists. The mechanism of this effect is unknown. Importantly, WM recovery occurs even before restoration of NMDAR blockade-induced molecular alterations, including reduced GAD67 in interneurons. Our insight into the cognitive-enhancing effect of α7 nAChR agonists, particularly in the animal models of SP, combines reviews of recent findings on glutamate and nicotinic receptor expression in the neuronal circuits involved in WM, the properties of these receptors, their implication in WM regulation, generation of rhythmic neuronal activity, resulting in a proposed hypothesis for further investigations. We suggest that (1) cortical/hippocampal interneurons, particularly PV positive, play a crucial role in WM and that impairment of these cells in SP could be behind the WM deficit; (2) activation of α7 nAChRs could restore calcium signaling and intrinsic properties of these interneurons, and associated with these events, computational capacity, gamma rhythmic activity, and WM would also be restored.

Activation of thalamocortical networks by the N-methyl-D-aspartate receptor antagonist phencyclidine: reversal by clozapine

BACKGROUND

Noncompetitive N-methyl-D-aspartate receptor antagonists are widely used as pharmacological models of schizophrenia. Their neurobiological actions are still poorly understood, although the prefrontal cortex (PFC) appears as a key target area.

METHODS

We examined the effect of phencyclidine (PCP) on neuronal activity of the mediodorsal (MD) and centromedial (CM) thalamic nuclei, reciprocally connected with the PFC, using extracellular recordings (n = 50 neurons from 35 Wistar rats) and c-fos expression.

RESULTS

Phencyclidine (.25 mg/kg intravenous [IV]) markedly disorganized the activity of MD/CM neurons, increasing (424%) and decreasing (41%) the activity of 57% and 20% of the recorded neurons, respectively (23% remained unaffected). Phencyclidine reduced delta oscillations (.15-4 Hz) as assessed by recording local field potentials. The subsequent clozapine administration (1 mg/kg IV) reversed PCP effects on neuronal discharge and delta oscillations. Double in situ hybridization experiments revealed that PCP (10 mg/kg intraperitoneal [IP]) markedly increased c-fos expression in glutamatergic neurons of several cortical areas (prefrontal, somatosensory, retrosplenial, entorhinal) and in thalamic nuclei, including MD/CM. Phencyclidine also increased c-fos expression in the amygdala; yet, it had a small effect in the hippocampus. Phencyclidine did not increase c-fos expression in gamma-aminobutyric acidergic cells except in hippocampus, amygdala, somatosensory, and retrosplenial cortices. Clozapine (5 mg/kg IP) had no effect by itself but significantly prevented PCP-induced c-fos expression.

CONCLUSIONS

Phencyclidine likely exerts its psychotomimetic action by increasing excitatory neurotransmission in thalamo-cortico-thalamic networks involving, among others, PFC, retrosplenial, and somatosensory cortices. The antipsychotic action of clozapine includes, among other actions, an attenuation of the neuronal hyperactivity in thalamocortical networks.

Clinical physiology and mechanism of dizocilpine (MK-801): electron transfer, radicals, redox metabolites and bioactivity

Dizocilpine (MK-801), an extensively investigated drug possessing secondary amine and benzenoid functions, displays a wide array of biological properties, including anticonvulsant and anesthetic. There is scant discussion of biomechanism. A relevant, important finding is formation of oxidative metabolites in the hydroxylamine and phenolic categories. Analogy to cocaine metabolites suggests participation of redox entities, such as, hydroxylamine, nitroxide and nitrosonium, which can lead to electron transfer and radical formation. There is also similarity to metabolism by 3,3′-iminodipropionitrile and phencyclidine. Alternatively, the phenolic metabolites are well-known precursors of ET quinones. The review documents various physiological effects, mainly involving the central nervous system. Also of interest are the pro- and anti-oxidant properties. Considerable attention has been paid to MK-801 as an antagonist of the N-methyl-D-aspartate receptor in the glutamate category. This aspect is often associated with effects on the central nervous system. The review also provides recent literature dealing with MK-801/NMDA receptor in various areas of bioactivity. Studies were made of MK-801 involvement in working memory processing. Deficits in behavior were noted after administration of the drug. Treatment of mice with dizocilpine induced learning impairment. The influence of MK-801 on fear has been investigated. The substance is known to exert an analgesic effect in pain control. A number of reports deal with anesthetic properties.

Neurodegeneration and prolonged immediate early gene expression throughout cortical areas of the rat brain following acute administration of dizocilpine

N-methyl-d-aspartate receptor antagonist drugs (NMDA-A), such as dizocilpine (MK801), induce long-lasting behavioral disturbances reminiscent to psychotic disorders in humans. To identify cortical structures affected by NMDA-A, we used a single dose of MK801 (10 mg/kg) that caused low and high neurodegeneration in intact and orchiectomized male rats, respectively. Degenerating somas (neuronal death) and axonal/synaptic endings (terminal degeneration) were depicted by a silver technique, and functionally affected cortical neuronal subpopulations by Egr-1, c-Fos, and FosB/DeltaFosB-immunolabeling. In intact males, MK801 triggered a c-Fos induction that remained high for more than 24 h in selected layers of the retrosplenial, somatosensory and entorhinal cortices. MK801-induced neurodegeneration reached its peak at 72 h. Degenerating somas were restricted to layer IV of the granular subdivision of the retrosplenial cortex, and were accompanied by suppression of Egr-1 immunolabeling. Terminal degeneration extended to selected layers of the retrosplenial, somatosensory and parahippocampal cortices, which are target areas of retrosplenial cortex. Induction of FosB/DeltaFosB by MK801 also extended to the same cortical layers affected by terminal degeneration, likely reflecting the damage of synaptic connectivity. In orchiectomized males, the neurodegenerative and functional effects of MK801 were exacerbated. Degenerative somas in layer IV of the retrosplenial cortex significantly increased, with a parallel enhancement of terminal degeneration and FosB/DeltaFosB-expression in the mentioned cortical structures, but no additional areas were affected. These observations reveal that synaptic dysfunction/degeneration in the retrosplenial, somatosensory and parahippocampal cortices might underlie the long-lasting impairments induced by NMDA-A.

Reduction in the protein level of c-Jun and phosphorylation of Ser73-c-Jun in rat frontal cortex after repeated MK-801 treatment

Repeated administration of NMDA antagonists can induce behavioral alterations that mimic symptoms of psychosis, as seen in schizophrenia. JNK, one of the MAPKs, and c-Jun, its downstream target molecule, play important roles in regulating apoptosis in neural cells, and have been suggested as being associated with the pathophysiology of psychosis and the mechanism of action of some antipsychotics. We investigated changes in the JNK-c-Jun pathway and other Jun family proteins in the rat frontal cortex after single and repeated administration of MK-801 to examine acute and chronic responses. Neither the protein level nor the phosphorylation of JNK changed after single or repeated doses of MK-801. However, after repeated treatments, but not a single treatment, with MK-801, a down-regulation occurred in the protein level and of Ser73 phosphorylation of c-Jun in the rat frontal cortex. Other members of the Jun family, JunB and JunD, were unchanged. Repeated exposure to MK-801 down-regulated the phosphorylation and protein level of c-Jun in the rat frontal cortex, which may be related to the long-term effects of chronic treatment with MK-801.

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.

Social memory in mice: disruption with an NMDA antagonist and attenuation with antipsychotic drugs

Social recognition reflects the ability of one animal to learn and remember the identity of another. Animal models of social learning and memory are pertinent to several different CNS diseases involving disruptions in cognition. Moreover, the increased understanding of the basic biology of memory increases the likelihood of discovery of memory-enhancing treatments in these human diseases. In the present study, we investigated the effects of the non-competitive NMDA antagonist ketamine on social recognition in mice across a broad dose range (5-30 mg/kg) and time-course (60 min-7 days). We also tested the ability of two antipsychotic drugs, haloperidol and olanzapine, to block the ketamine effect. Our results show that mice demonstrate social recognition over a several day period, with loss of recognition between 3-7 days. Ketamine disrupts social memory at doses which do not affect task performance. Chronic oral administration of haloperidol or olanzapine attenuates these ketamine-induced effects on social recognition, tending to normalize the memory behavior. The neural mechanisms of these actions are not known, although medial temporal lobe memory systems have been implicated.

Lamotrigine prevents MK801-induced alterations in early growth response factor-1 mRNA levels and immunoreactivity in the rat brain

MK801 (dizocilpine) induces selective neurotoxic effects in the retrosplenial cortex, ranging from neuronal vacuolization to irreversible neurodegeneration depending on the dose administered. Although lamotrigine prevents MK801-induced neuronal vacuolization in the retrosplenial cortex 4 h after injection, it is not clear whether lamotrigine attenuates the subsequent neurodegeneration that occurs 3-4 days later. Because early growth response factor-1 (egr-1) plays a key role in neurodegeneration and its expression is induced in the retrosplenial cortex following MK801 treatment, it is possible that lamotrigine may attenuate MK801-induced neurodegeneration via inhibition of egr-1 expression in the retrosplenial cortex. To address this issue, we treated rats with lamotrigine (10 or 20 mg/kg) followed by MK801 (2 mg/kg) and measured changes in the levels of egr-1 mRNA and immunoreactivity in the retrosplenial cortex and other brain regions 3 h later. We also evaluated the effects of these treatments on neurodegeneration 4 days following treatment using Fluoro-Jade B staining. MK801 treatment increased egr-1 mRNA and immunoreactivity in the restrosplenial, cingulate, entorhinal and piriform cortices, but decreased levels in hippocampal subfields. These MK801-induced changes in egr-1 expression were significantly inhibited by lamotrigine pretreatment. In addition, MK801-induced neurodegeneration in the retrosplenial cortex was partially blocked by lamotrigine pretreatment in a dose dependent manner. These results demonstrate that lamotrigine pretreatment prevents the MK801-induced upregulation of egr-1 expression in a region-selective manner, and suggest that this effect may contribute, in part, to the attenuation of MK801-induced neurodegeneration in the retrosplenial cortex.

Comparison between intraperitoneal and subcutaneous phencyclidine administration in Sprague-Dawley rats: a locomotor activity and gene induction study

In a putative model of acute phencyclidine (PCP)-induced psychosis we evaluated effects of the drug on locomotor activity (LMA) and immediate early gene (IEG) induction in the rat using two routes of drug administration, intraperitoneal (i.p.) and subcutaneous (s.c.). Adult male rats received saline or PCP (1.0-5.0 mg/kg) either i.p or s.c. and were assessed for LMA for 60 min. At the end of the LMA testing animals were culled and blood and brain samples were collected for PCP concentration analysis. Separate cohorts of animals received 5.0 mg/kg PCP (i.p. or s.c.) and were used to investigate (1) the pharmacokinetics of PCP or (2) induction of IEG (Arc, c-fos, BDNF, junB, Krox-20, sgk-1, NURR1, fra-2, Krox-24, and egr-3) mRNA expression in the prefrontal cortex (PFC). Administration of PCP resulted in locomotor hyperactivity which was more robust and longer-lasting in animals dosed s.c. compared to i.p.-treated-animals. Differences in hyperlocomotion were paralleled by higher concentrations of PCP in the blood and in the brain of s.c.-treated animals compared to i.p.-treated animals. The differences in the concentration of PCP between the two routes of administration were detected 30 min after dosing and persisted for up to 4 h. Administration of PCP via the s.c. route resulted in induction of more IEGs and consistently larger magnitudes of induction than that via the i.p. route. Therefore, we have outlined the dosing conditions to induce rapid and robust effect of acute PCP on behaviour, gene induction, and pharmacokinetic profile, to allow investigation of this as a potential animal model of acute psychosis.

Acute D2/D3 dopaminergic agonism but chronic D2/D3 antagonism prevents NMDA antagonist neurotoxicity

BACKGROUND

Antagonists of the N-methyl-D-aspartate (NMDA) glutamate receptor, most likely by producing disinhibtion in complex circuits, acutely produce psychosis and cognitive disturbances in humans, and neurotoxicity in rodents. Studies examining NMDA Receptor Hypofunction (NRHypo) neurotoxicity in animals, therefore, may provide insights into the pathophysiology of psychotic disorders. Dopaminergic D2 and/or D3 agents can modify psychosis over days to weeks, suggesting involvement of these transmitter system(s).

METHODS

We studied the ability of D2/D3 agonists and antagonists to modify NRHypo neurotoxicity both after a one-time acute exposure and after chronic daily exposure.

RESULTS

Here we report that D2/D3 dopamine agonists, probably via D3 receptors, prevent NRHypo neurotoxicity when given acutely. The protective effect with D2/D3 agonists is not seen after chronic daily dosing. In contrast, the antipsychotic haloperidol does not affect NRHypo neurotoxicity when given acutely at D2/D3 doses. However, after chronic daily dosing of 1, 3, or 5 weeks, haloperidol does prevent NRHypo neurotoxicity with longer durations producing greater protection.

CONCLUSIONS

Understanding the changes that occur in the NRHypo circuit after chronic exposure to dopaminergic agents could provide important clues into the pathophysiology of psychotic disorders.

Dose-response characteristics of ketamine effect on locomotion, cognitive function and central neuronal activity

The present dose-response study sought to determine the effects of subanesthetic dosages (4-16 mg/kg) of ketamine on locomotion, sensorimotor gating (PPI), working memory, as well as c-fos expression in various limbic regions implicated in the pathogenesis of schizophrenia. In addition, we examined whether ketamine-induced locomotion was influenced by the dark/light cycle. We found that ketamine increased locomotor activity in a dose dependent manner, but found no influence of the dark-light cycle. Additionally, ketamine dose-dependently interrupted PPI, resulting in prepulse facilitation at doses of 8 and 12 mg/kg. The dose of 12 mg/kg also induced impairments in working memory assessed by the discrete-trial delayed-alternation task. C-fos expression indicated that the dose-dependent behavioral effects of ketamine might be related to changes in the activity of limbic regions, notably hippocampus and amygdala.

Impairment in perceptual attentional set-shifting following PCP administration: a rodent model of set-shifting deficits in schizophrenia

RATIONALE

Impaired ability to shift perceptual attentional set forms a core feature of schizophrenic illness and is associated with prefrontal cortical dysfunction. A pharmacological model producing equivalent deficits in rodents may enable the development of novel therapeutic strategies for effective treatment of cognitive impairments in schizophrenia.

OBJECTIVE

This study was designed to investigate the effects of phencyclidine (PCP) administration on performance in a rodent attentional set-shifting task and the neural correlates of PCP-induced deficits in task performance.

METHODS

Twenty-four hours following acute administration of 2.58 mg/kg PCP or vehicle, rats were tested on a perceptual attentional set shifting task (Birrell and Brown in J Neurosci 20:4320-4324, 2000). Following completion of the task, in situ hybridisation was employed to detect concurrent regional alterations in zif-268 and parvalbumin mRNA expression.

RESULTS

PCP administration selectively decreased the ability of rats to shift attentional set between perceptual dimensions (extra-dimensional shift, EDS). This impairment was accompanied by, and correlated with, decreases in expression of zif-286 in the infralimbic cortex and of parvalbumin in the dorsal reticular nucleus of the thalamus.

CONCLUSION

Acute administration of PCP produces deficits in perceptual set shifting comparable to an aspect of executive dysfunction in schizophrenia. Moreover, this impairment is associated with altered medial prefrontal cortical and reticular thalamic activity. Therefore, this rodent paradigm may model the set-shifting deficits that form a core feature of schizophrenic pathology.

A gene for neuronal plasticity in the mammalian brain: Zif268/Egr-1/NGFI-A/Krox-24/TIS8/ZENK?

Zif268 is a transcription regulatory protein, the product of an immediate early gene. Zif268 was originally described as inducible in cell cultures; however, it was later shown to be activated by a variety of stimuli, including ongoing synaptic activity in the adult brain. Recently, mice with experimentally mutated zif268 gene have been obtained and employed in neurobiological research. In this review we present a critical overview of Zif268 expression patterns in the naive brain and following neuronal stimulation as well as functional data with Zif268 mutants. In conclusion, we suggest that Zif268 expression and function should be considered in a context of neuronal activity that is tightly linked to neuronal plasticity.

Phencyclidine-induced changes in rat cortical gene expression identified by microarray analysis: implications for schizophrenia

Acute phencyclidine induces schizophrenia-like symptoms in healthy humans and psychotic episodes in schizophrenics. Although phencyclidine is known as a N-methyl d-aspartate receptor antagonist (NMDA-R), the molecular events underlying the behavioral symptoms remain largely unknown. Statistical analysis of oligonucleotide microarray data was used to identify phencyclidine-induced alterations in rat cortical gene expression. Acute phencyclidine produced a statistically significant change in 477 genes in rat prefrontal cortex (PFC), a brain area associated with cognitive dysfunction in schizophrenics. Real-time quantitative PCR (RTQ-PCR) confirmed a subset of these changes ranging from -59% to 255% (smallest confirmation: -19%). Subsequent time-course and dose-response studies using RTQ-PCR confirmed and extended the original microarray results. At the molecular level, genes altered by phencyclidine are related to diverse biological processes including stress, inflammatory response, growth and development, neural plasticity and signal transduction. Further analysis, aimed at assessing the relevance of our results to schizophrenia, revealed dysregulation of genes related to: (i) thalamocortical projections, (ii) neurotransmission and neuromodulation, (iii) thyroid hormone activity, (iv) oligodendrocyte linage, (v) brain lipid metabolism, (vi) sleep architecture and (viii) the velocardiofacial syndrome.

The NMDA receptor hypofunction model of psychosis

Antagonists of the NMDA glutamate receptor, including phencyclidine (PCP), ketamine, and CGS-19755, produce cognitive and behavioral changes in humans. In rodents these agents produce a myriad of histopathological and neurochemical changes. Several lines of evidence suggest that a large number of these drug-induced effects are dose-dependent manifestations of the same general disinhibition process in which NMDA antagonists abolish GABAergic inhibition, resulting in the simultaneous excessive release of acetylcholine and glutamate. Progressive increases in the severity of NMDA receptor hypofunction (NRHypo) within the brain produce an increasing range of effects on brain function. Underexcitation of NMDA receptors, induced by even relatively low doses of NMDA antagonist drugs, can produce specific forms of memory dysfunction without clinically evident psychosis. More severe NRHypo can produce a clinical syndrome very similar to a psychotic schizophrenic exacerbation. Finally, sustained and severe NRHypo in the adult brain is associated with a form of neurotoxicity with well-characterized neuropathological features. In this paper several of these effects of NMDA antagonists and a likely mechanism responsible for producing them will be reviewed. In addition the possible role of NRHypo in the pathophysiology of idiopathic psychotic disorders will be considered.

Withdrawal from chronic phencyclidine treatment induces long-lasting depression in brain reward function

Phencyclidine (PCP) is a drug of abuse that has rewarding and dysphoric effects in humans. The complex actions of PCP, and PCP withdrawal in particular, on brain reward function remain unclear. The purpose of the present study was to characterize the effects of withdrawal from acute and chronic PCP treatment on brain reward function in rats. A brain stimulation reward procedure was used to evaluate the effects of acute PCP injection (0, 5, or 10 mg/kg) or chronic PCP treatment (0, 10, 15, or 20 mg/kg/day for 14 days delivered via subcutaneous osmotic minipumps) on brain reward function. Withdrawal from acute administration of 5 and 10 mg/kg PCP produced a decrease in brain reward function as indicated by a sustained elevation in brain reward thresholds. When administered chronically, 10, 15, or 20 mg/kg/day PCP induced a progressive dose-dependent potentiation of brain stimulation reward, while cessation of the treatment resulted in significant elevations in reward thresholds reflecting diminished reward. Specifically, withdrawal from 15 or 20 mg/kg/day PCP induced a depression in brain reward function that lasted for the entire month of observation. These results indicate that prolonged continuous administration of high PCP doses facilitates brain stimulation reward, while withdrawal from acute high PCP doses or chronic PCP treatment results in a protracted depression of brain reward function that may be analogous to the dysphoric and anhedonic symptoms observed in PCP dependence, depression, and schizophrenia.

Effect of amphetamine and phencyclidine on DNA-binding activities of serum response and dyad symmetry elements

Acute administration of D-amphetamine sulphate (AMPH) and (1-[1-phenylcyclohexyl]piperidine hydrochloride) (phencyclidine; PCP) produces a characteristic spatio-temporal distribution of c-Fos protein in the brain. As transcriptional mechanisms underlying the induction of c-fos gene expression may be regulated in a stimulus-specific manner, we have analyzed the binding activities of serum response element (SRE), dyad symmetry element (DSE) and calcium response element (CRE), the major regulatory sites of the c-fos promoter. Electrophoretic mobility shift showed that SRE binding activity was increased for 50-60%, 2-6h after AMPH, while treatment with PCP resulted in light decrease of SRE binding activity throughout the same time period. Co-administration of AMPH and PCP induced gradual increase of SRE binding activity, reaching maximum (86%) at 6h. Binding of nuclear proteins to DSE sequence was increased 1-2h after administration of AMPH (72-87%) and remained elevated till the end of the time window observed. PCP and AMPH/PCP caused different temporal profile of DSE binding with peak (40-54%) 4-6h after administration. In contrast, DNA-binding activity of the CRE sequences remained unchanged throughout the time period of 6h under all conditions. Finally, supershift analysis clearly demonstrated presence of SRF and c-Fos protein in the transcriptional complexes bound to SRE and DSE sequences irrespective to AMPH, PCP or combined treatment. These findings also showed that the presence of c-Fos protein in SRE and DSE nucleocomplex support the hypothesis concerning autoregulation of c-fos gene expression during psychostimulant action in vivo.

NMDA-antagonist MK-801-induced neuronal degeneration in Wistar rat brain detected by the Amino-Cupric-Silver method

The neurotoxic effect following a single intraperitoneal injection of MK-801 (10 mg/kg) in adult female Wistar rats at different survival times was studied with the 1994 version of de Olmos' Amino-Cupric-Silver (A-Cu-Ag) technique for detection of neural degeneration. In addition to the well documented somatodendritic degeneration observable in cortical olfactory structures, dentate gyrus, retrosplenial and sensory cortices, we detected this type of neuronal degeneration also in the main olfactory bulb, motor and anterior cingulate cortices, thalamus and cerebellum. Terminal degeneration, not reported by previous authors, was detected in cortical olfactory structures, hippocampal formation, sensory, infralimbic, prelimbic, agranular insular, ectorhinal, perirhinal and lateral orbital cortices. These results demonstrate that the A-Cu-Ag procedure is more efficient than other silver methods for detecting the degeneration induced by MK-801. In fact, the use of the A-Cu-Ag method has made it possible to infer the connectional relations between the damaged cell bodies and corresponding terminal degeneration. Our results also indicate that the A-Cu-Ag technique may be a suitable method for the staining of neurons undergoing apoptotic-like degeneration. The probable degenerative mechanism of MK-801 in the main olfactory system is discussed.

Induction of metabolic hypofunction and neurochemical deficits after chronic intermittent exposure to phencyclidine: differential modulation by antipsychotic drugs

Numerous human imaging studies have revealed an absolute or relative metabolic hypofunction within the prefrontal cortex, thalamus and temporal lobes of schizophrenic patients. The former deficit correlates with cognitive deficits and negative symptoms, whereas the latter correlates with positive symptomologies. There is also general consensus that schizophrenia is associated with decreased parvalbumin expression in the prefrontal cortex. Since the drug phencyclidine can induce a psychosis resembling schizophrenia in humans, we have examined whether repeated phencyclidine (PCP) treatment to rats could produce similar metabolic and neurochemical deficits to those occurring in schizophrenia and whether these deficits could be modulated by antipsychotic drugs. We demonstrate here that chronic intermittent exposure to PCP (2.58 mg kg(-1) i.p.) elicits a metabolic hypofunction, as demonstrated by reductions in the rates of glucose utilization, within the prefrontal cortex, reticular nucleus of thalamus and auditory system, key structures displaying similar changes in schizophrenia. Moreover, chronic PCP treatment according to this regime also decreases parvalbumin mRNA expression in the rat prefrontal cortex and reticular nucleus of the thalamus. Chronic coadministration of haloperidol (1 mg kg(-1) day(-1)) or clozapine (20 mg kg(-1) day(-1)) with PCP did not modulate PCP-induced reductions in metabolic activity in the rat prefrontal cortex, but reversed deficits in the structures of the auditory system. Clozapine, but not haloperidol, reversed PCP-induced decreases in parvalbumin expression in prefrontal cortex GABAergic interneurons, whereas both drugs reversed the deficits in the reticular nucleus of the thalamus. These data provide important new information, which strengthen the validity of chronic PCP as a useful animal model of schizophrenia, when administered according to this protocol. Furthermore, we propose that reversal of PCP-induced reductions in parvalbumin expression in the prefrontal cortex may be a potential marker of atypical antipsychotic activity in relation to amelioration of cognitive deficits and negative symptoms of schizophrenia.

Acute and delayed effects of phencyclidine upon mRNA levels of markers of glutamatergic and GABAergic neurotransmitter function in the rat brain

Glutamatergic and GABAergic neurotransmitter systems exist in equilibrium to maintain "normal" brain function. Evidence is accumulating that disturbance of this equilibrium may be one of the key factors giving rise to schizophrenia. While there is widespread evidence that the psychotomimetic phencyclidine (PCP) induces schizophrenia-related symptoms, it is not clear how this dramatic effect is mediated. This study was designed to investigate acute and delayed effects of PCP on the mRNA expression of a range of markers of neuronal function associated with the glutamatergic and GABAergic systems within the rat brain. The mRNA levels of CaMKIIalpha, an enzyme which is located within the postsynaptic density and phosphorylates AMPA receptors, remained unaltered both 2 and 24 h posttreatment. Homer 1a, an immediate early gene associated with metabotropic glutamate receptors within the postsynaptic density, displayed region-specific differential changes within the prefrontal, primary auditory, and retrosplenial cortices 2 and 24 h posttreatment. Parvalbumin, a calcium-binding protein located within a subpopulation of GABAergic interneurones, displayed altered mRNA levels within the reticular nucleus of the thalamus at 2 and 24 h posttreatment and the substantia nigra pars reticulata 24 h posttreatment only. These phencyclidine-induced changes in mRNA expression were not accompanied by any changes in hsp-70 mRNA levels, a marker of NMDA antagonist-induced reversible neurotoxicity. These results indicate that the glutamatergic (group I metabotropic glutamate receptors) and GABAergic (parvalbumin-containing interneurones) neurotransmitter systems are differentially modulated in a region- and time-dependent manner by exposure to phencyclidine.

Integrative role for serotonergic and glutamatergic receptor mechanisms in the action of NMDA antagonists: potential relationships to antipsychotic drug actions on NMDA antagonist responsiveness

NMDA receptor antagonists worsen symptoms in schizophrenia and induce schizophrenic-like symptoms in normal individuals. In animals, NMDA antagonist-induced behavioral responses include increased activity, head weaving, deficits in paired pulse inhibition and social interaction, and increased forced swim immobility. Repeated exposure to NMDA antagonists in animals results in behavioral sensitization-a phenomenon accentuated in rats with dopaminergic neurons lesioned during development. In keeping with an involvement of serotonin and glutamate release in NMDA antagonist action, selected behaviors induced by NMDA antagonists are minimized by 5-HT(2A) receptor antagonists and mGLU2 receptor agonists. These observations provide promising new approaches for treating acute NMDA antagonist-induced psychosis. Further, acute atypical antipsychotic drugs also minimize NMDA antagonist actions to a greater degree than typical antipsychotics. However, because knowledge concerning acute versus chronic effectiveness of various antipsychotic drugs against NMDA antagonist neuropathology is limited, future studies to define more fully the basis of their differences in efficacy after chronic treatment could provide an understanding of their actions on neural mechanisms responsible for the core pathogenesis of 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.

Expression of c-Fos, Fos B, Jun B, and Zif268 transcription factor proteins in rat barrel cortex following apomorphine-evoked whisking behavior

Apomorphine-evoked expression of transcription factor proteins: c-Fos, Fos B, Jun B, and Zif268 (also named Krox-24, NGFI-A, Egr-1), was investigated in rat somatosensory (barrel) cortex. The effect of the N-methyl-D-aspartate receptor antagonist MK-801 on their expression was also analyzed. Apomorphine is a dopamine receptor agonist, eliciting motor activity, including enhanced whisking leading to the activation of vibrissae representation in the barrel cortex. Rats had their whiskers clipped on one side of the snout. The Zif268 levels were markedly reduced by this procedure alone. In contrast, apomorphine (5.0 mg/kg) evoked marked c-Fos elevation, less pronounced changes in Jun B and Zif268 and no change in Fos B. The greatest apomorphine-evoked c-Fos accumulation was observed in layers IV and V/VI of non-deprived barrel cortex and was not significantly influenced by MK-801 injection at 0.1 mg/kg. A higher dose of MK-801 (1.0 mg/kg) produced abnormalities in locomotor behavior and diminished c-Fos levels on the non-deprived side to the ones observed in the sensory stimulus-deprived cortex. We conclude that the response of the somatosensory cortex is selective with respect to both the gene activated and its cortical layer localization. Furthermore, sensory stimulation provides a major but not the only component to apomorphine-evoked barrel cortex gene activation.

Differential regulation of chromogranin A, chromogranin B and secretogranin II in rat brain by phencyclidine treatment

Chromogranin A, chromogranin B and secretogranin II belong to the chromogranin family which consists of large protein molecules that are found in large dense core vesicles. Chromogranins are endoproteolytically processed to smaller peptides. This study was designed to elucidate the regulation of chromgranin expression by acute and subchronic phencyclidine administration. The behavioral syndrome produced by phencyclidine represents a pharmacological model for some aspects of schizophrenia [Jentsch and Roth (1999) Neuropsychopharmacology 20, 201-225]. Tissue concentrations of chromogranins were measured with specific radioimmunoassays. Alterations in secretogranin II gene expression were investigated by in situ hybridization. A single dose of phencyclidine (10mg/kg) led to a transient decrease in secretoneurin tissue levels in the prefrontal cortex after 4h followed by an increase in secretoneurin tissue levels after 12h. Repeated phencyclidine treatment (10mg/kg/day) for five days resulted in elevated secretoneurin levels in cortical areas whereas chromogranin A and chromogranin B tissue levels were unchanged. After the same treatment, a significant increase in the number of secretoneurin containing neurons was found in cortical layers II-III, and V-VI as revealed by immunocytochemistry. The increases in secretoneurin levels were paralleled by an increased number of secretogranin II messenger RNA containing neurons as well as by an increased expression of secretogranin II by individual neurons. The present study shows that secretoneurin II tissue concentration and secretogranin II messenger RNA expression is distinctly altered after acute and subchronic phencyclidine application. From these results we suggest that phencyclidine may induce synaptic alterations in specific brain areas and may contribute to a better understanding of synaptic dysfunction which may also occur in schizophrenia.

Traditional and new antipsychotic drugs differentially alter neurotransmission markers in basal ganglia-thalamocortical neural pathways

The effects of three chronically administered antipsychotic drugs on selected neurochemical markers of dopaminergic and GABAergic transmission were compared within the cerebral regions making up the basal ganglia-thalamocortical parallel processing neuronal pathways. All three drugs reduce psychosis in humans, whereas only haloperidol, but not olanzapine or sertindole, induce purposeless oral chewing movements (CMs) in rats or cause high rates of parkinsonism or tardive dyskinesia in humans. Male Sprague Dawley rats were treated with haloperidol, sertindole, or olanzapine delivered in drinking water for 6 months at doses which produce drug plasma levels in rat in the human therapeutic range. Results show the expected dopamine D2 receptor upregulation in striatum predominantly with haloperidol, although mild D2 upregulation was apparent in striatum after olanzapine. GAD67 mRNA was increased in striatum and decreased in globus pallidus by haloperidol and sertindole, but not by olanzapine. In the substantia nigra pars reticulata (SNR), both olanzapine and sertindole failed to induce GABA(A) receptor upregulation or D1 receptor downregulation, but haloperidol did both, confirming a previous report. In thalamus, all three drugs increased GAD expression in the reticular nucleus, whereas only haloperidol decreased GABA(A) binding in the mediodorsal nucleus, actions consistent with a reduction in nigrothalamic, GABA-mediated neural transmission. These results are consistent with the idea that the two new antipsychotics tested have mild and regionally restricted actions within the basal ganglia nuclei and a common action on increasing GAD expression in the reticular nucleus of the thalamus (RtN). Haloperidol, in contrast, has a broad and potent action in basal ganglia, causing changes in SNR and in the mediodorsal nucleus, while also altering GAD mRNA in RtN, potentially reflective of its dyskinetic and antipsychotic actions.

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

In this study, we examined the effect of clozapine, olanzapine, risperidone and haloperidol on the neuropathology (i.e. neuronal vacuolization) and the expression of Fos-like protein and c-fos mRNA in the retrosplenial cortex of female Sprague-Dawley rats induced by the NMDA receptor antagonist dizocilpine. Pretreatment (15 min) with clozapine or olanzapine, but not risperidone or haloperidol, blocked the neuronal vacuolization produced by dizocilpine (0.5 mg/kg, s.c.) in the rat retrosplenial cortex in a dose-dependent manner. Furthermore, pretreatment (15 min) with clozapine or olanzapine, but not risperidone or haloperidol, significantly attenuated the expression of Fos-like protein in the retrosplenial cortex induced by dizocilpine (0.5 mg/kg, s.c.) in a dose-dependent manner. The marked expression of c-fos mRNA in the rat retrosplenial cortex induced by the administration of dizocilpine (0.5 mg/kg, s.c.) was significantly attenuated by pretreatment (15 min) with clozapine (10 mg/kg) or olanzapine (10 mg/kg), but not risperidone (10 mg/kg) or haloperidol (10 mg/kg). The present results suggest that pharmacologically relevant doses of clozapine or olanzapine, but not risperidone or haloperidol, block the neuropathological changes and the expression of Fos-like protein and c-fos mRNA in the rat retrosplenial cortex elicited by the administration of dizocilpine. It is possible that the blockade of dizocilpine-induced neuropathological changes by clozapine and olanzapine may be related to the unique antipsychotic actions of these drugs in schizophrenic patients, although this remains to be verified.

The selective vulnerability of striatopallidal neurons

The different types of striatal neuron show a range of vulnerabilities to a variety of insults. This can be clearly seen in Huntington's disease where a well mapped pattern of pathological events occurs. Medium spiny projection (MSP) neurons are the first striatal cells to be affected as the disease progresses whilst interneurons, in particular the NADPH diaphorase positive ones, are spared even in the late stages of the disease. The MSP neurons themselves are also differentially affected. The death of MSP neurons in the patch compartment of the striatum precedes that in the matrix compartment and the MSP neurons of the dorsomedial caudate nucleus degenerate before those in the ventral lateral putamen. The enkephalin positive striatopallidal MSP neurons are also more vulnerable than the substance P/dynorphin MSP neurons. We review the potential causes of this selective vulnerability of striatopallidal neurons and discuss the roles of endogenous glutamate, nitric oxide and calcium binding proteins. It is concluded that MSP neurons in general are especially susceptible to disruptions of cellular respiration due to the enormous amount of energy they expend on maintaining unusually high transmembrane potentials. We go on to consider a subpopulation of enkephalinergic striatopallidal neurons in the rat which are particularly vulnerable. This subpopulation of neurons readily undergo apoptosis in response to experimental manipulations which affect dopamine and/or corticosteroid levels. We speculate that the cellular mechanisms underlying this cell death may also operate in degenerative disorders such as Huntington's disease thereby imposing an additional level of selectivity on the pattern of degeneration. The possible contribution of the selective death of striatopallidal neurons to a number of clinically important psychiatric conditions including obsessive compulsive disorders and Tourette's syndrome is also discussed.

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.

The NMDA receptor antagonist CPP impairs conditioned taste aversion and insular cortex long-term potentiation in vivo

It has been proposed that long-term potentiation (LTP) a form of activity-dependent modification of synaptic efficacy, may be a synaptic mechanism for certain types of learning. Recent studies on the insular cortex (IC) a region of the temporal cortex implicated in the acquisition and storage of conditioned taste aversion (CTA), have demonstrated that tetanic stimulation of the basolateral nucleus of the amygdala (Bla) induce an N-methyl-d-aspartate (NMDA) dependent LTP in the IC of adult rats in vivo. Here we present experimental data showing that intracortical administration of the NMDA receptor competitive antagonist CPP (-3(-2 carboxipiperazin-4-yl)-propyl-1-phosphonic acid) disrupts the acquisition of conditioned taste aversion, as well as, the IC-LTP induction in vivo. These findings are of particular interest since they provide support for the view that the neural mechanisms underlying NMDA dependent neocortical LTP, constitute a possible mechanism for the learning related functions performed by the IC.

Localization of PKN mRNA in the rat brain

Distribution of mRNA encoding PKN, a fatty acid and RhoA-activated serine/threonine protein kinase with a catalytic domain highly homologous to that of protein kinase C, was investigated in the rat brain using in situ hybridization histochemistry. PKN mRNA proved to be heterogenously distributed. The highest signals were observed in the cerebellum, in limbic systems such as olfactory bulb, hippocampal formation and limbic cortex, and in regions involved in central autonomic and neuroendocrine functions, such as hypothalamic ventromedial, dorsomedial, lateroanterior and arcuate nuclei, paraventricular hypothalamic nucleus and locus coeruleus. PKN mRNA was also highly expressed in dopaminergic neurons such as the ventral tegmental area and substantia nigra pars compacta, in serotonergic raphe neurons, and in cholinergic neurons such as nucleus diagonal band, nucleus basalis, and lateral dorsal tegmental nucleus. The distribution of PKN mRNA differed from that for PKC isoforms. As the localization of PKN mRNA is heterogeneous, PKN may have a specific role in distinct populations of nerve cells.