Enhancement of immobility induced by repeated phencyclidine injection: association with c-Fos protein in the mouse brain

Interneuron Heterotopia in the Lis1 Mutant Mouse Cortex Underlies a Structural and Functional Schizophrenia-Like Phenotype

LIS1 is one of the principal genes related to Type I lissencephaly, a severe human brain malformation characterized by an abnormal neuronal migration in the cortex during embryonic development. This is clinically associated with epilepsy and cerebral palsy in severe cases, as well as a predisposition to developing mental disorders, in cases with a mild phenotype. Although genetic variations in the LIS1 gene have been associated with the development of schizophrenia, little is known about the underlying neurobiological mechanisms. We have studied how the Lis1 gene might cause deficits associated with the pathophysiology of schizophrenia using the Lis1/sLis1 murine model, which involves the deletion of the first coding exon of the Lis1 gene. Homozygous mice are not viable, but heterozygous animals present abnormal neuronal morphology, cortical dysplasia, and enhanced cortical excitability. We have observed reduced number of cells expressing GABA-synthesizing enzyme glutamic acid decarboxylase 67 (GAD67) in the hippocampus and the anterior cingulate area, as well as fewer parvalbumin-expressing cells in the anterior cingulate cortex in Lis1/sLis1 mutants compared to control mice. The cFOS protein expression (indicative of neuronal activity) in Lis1/sLis1 mice was higher in the medial prefrontal (mPFC), perirhinal (PERI), entorhinal (ENT), ectorhinal (ECT) cortices, and hippocampus compared to control mice. Our results suggest that deleting the first coding exon of the Lis1 gene might cause cortical anomalies associated with the pathophysiology of schizophrenia.

Repeated administration of propofol upregulated the expression of c-Fos and cleaved-caspase-3 proteins in the developing mouse brain

Objectives and Aim:

This study was designed to analyze the relationship between the expression of c-Fos protein and apoptosis in the hippocampus following propofol administration in infant mice. There are reports that certain drugs, including the general anesthetics applied in pediatrics and obstetrics, could block N-methyl-D-aspartate glutamate receptors and activate γ-aminobutyric acid type A receptors. Furthermore, some anesthetics could trigger neuroapoptosis and the expression of c-Fos in the developing rodent brain. Propofol is a general anesthetic increasingly used in pediatrics and obstetrics, and is reported to be able to interact with both γ-aminobutyric acid type A and N-methyl-D-aspartate glutamate receptors. No adequate evaluations have been available as to whether the dosage of propofol to maintain anaesthesia could trigger the expression of c-Fos and apoptosis.

Materials and Methods:

Intraperitoneal injections of propofol (50, 100 and 150 mg/kg) or vehicle were administered every 90 minutes (4 times) in infant mice (5–7 days old). 30 minutes after the final administration, the protein expressions of c-Fos and cleaved-caspase-3 in the hippocampus were determined by immunohistochemistry and Western blotting.

Results:

It was demonstrated that the expressions of cleaved-caspase-3 and c-Fos were upregulated in the hippocampal CA3 region in this study.

Conclusions:

The upregulated c-Fos expression induced by repeated injections of propofol might evoke neuroapoptosis.

Mouse strain differences in phencyclidine-induced behavioural changes

Administration of phencyclidine (PCP) is acknowledged to generate a model of psychosis in animals. With the identification of genetic susceptibility factors for schizophrenia and bipolar disorder, great efforts have been made to generate genetic animal models for major mental illnesses. As these disorders are multifactorial, comparisons among drug-induced (non-genetic) and genetic models are becoming an important issue in biological psychiatry. A major barrier is that the standard mouse strain used in the generation of genetic models is C57BL/6, whereas almost all studies with PCP-induced models have utilized other strains. To fill this technical gap, we systematically compared the behavioural changes upon PCP administration in different mouse strains, including C57BL/6N, C57BL/6J, ddY, and ICR. We observed strain differences in PCP-induced hyperlocomotion and enhanced immobility in the forced swim test (ddY>>C57BL/6N and 6J>ICR). In contrast, there was no strain difference in the impairment of recognition memory in the novel object recognition memory test after withdrawal of chronic PCP administration. This study provides practical guidance for comparing genetic with PCP-induced models of psychosis in C57BL/6. Furthermore, such strain differences may provide a clue to the biological mechanisms underlying PCP-induced endophenotypes possibly relevant to major mental illnesses.

The effects of phencyclidine (PCP) on anxiety-like behavior in the elevated plus maze and the light-dark exploration test are age dependent, sexually dimorphic, and task dependent

Previous research in our laboratory revealed sexually dimorphic effects of prior exposure to phencyclidine (PCP) on elevated plus maze behavior. In an attempt to examine the developmental time course of this effect and determine the extent to which it generalizes to other anxiety paradigms, young adult (61-64 days old) and adult (96-107 days old) male and female rats were treated with PCP (15 mg/kg) or saline. Following a two week withdrawal period, animals were tested in either the elevated plus maze (EPM) or a light-dark exploration (LD) test. In adults, both tests revealed a sexually dimorphic effect driven by PCP-induced decreases in anxiety in females as indicated by increased time spent in the open arms of the EPM and in the lit compartment of the LD test and increased anxiety in males as indicated by decreased time spent in the lit compartment of the LD. In young animals, PCP pretreatment decreased open arm exploration in the elevated plus maze, indicating increased anxiety. However, PCP increased time spent in the light compartment in the light-dark exploration test, indicating decreased anxiety. Corticosterone levels measured 15 min after the onset of the EPM failed to reveal an association between the behavioral effects of PCP and corticosterone levels. The results in adults substantiate the previously observed sexually dimorphic effect of PCP on elevated plus maze behavior in adults and indicate that the effect generalizes to another anxiety paradigm. The results in the younger animals suggest an age dependent effect of PCP on anxiety in general and indicate that behaviors in the elevated plus maze and the light-dark exploration test reflect dissociable psychobiological states.

Cannabinoid CB1 receptor antagonism prevents neurochemical and behavioural deficits induced by chronic phencyclidine

Clinical and laboratory studies suggest that the endocannabinoid system is involved in schizophrenia disorders. Recent evidence indicates that cannabinoid receptor (CB1) antagonists have a pharmacological profile similar to antipsychotic drugs. We investigated the behavioural and biochemical effects of the CB1 antagonist AM251 in a phencyclidine (PCP) animal paradigm modelling the cognitive deficit and some negative symptoms of schizophrenia. Chronic AM251 (0.5 mg/kg for 3 wk) improved the PCP-altered recognition memory, as indicated by a significant amelioration of the discrimination index compared to chronic PCP alone (2.58 mg/kg for 1 month). AM251 also reversed the PCP-induced increase in immobility in the forced swim test resembling avolition, a negative sign of schizophrenia. In order to analyse the mechanisms underlying these behaviours, we studied the effects of AM251 on the endocannabinoid system (in terms of CB1 receptor density and functional activity and endocannabinoid levels) and c-Fos protein expression. The antagonist counteracted the alterations in CB1 receptor function induced by PCP in selected cerebral regions involved in schizophrenia. In addition, in the prefrontal cortex, the key region in the integration of cognitive and negative functions, AM251 markedly raised anandamide levels and reversed the PCP-induced increase of 2-arachidonoylglycerol concentrations. Finally, chronic AM251 fully reversed the PCP-elicited expression of c-Fos protein in the prefrontal cortical region. These findings suggest an antipsychotic-like profile of the CB1 cannabinoid receptor antagonist which, by restoring the function of the endocannabinoid system, might directly or indirectly normalize some of the neurochemical maladaptations present in this schizophrenia-like animal model.

The atypical anxiolytic drug, tofisopam, selectively blocks phosphodiesterase isoenzymes and is active in the mouse model of negative symptoms of psychosis

Tofisopam is a member of the 2,3-benzodiazepine compound family which is marketed for the treatment of anxiety in some European countries. In contrast to classical 1,4-benzodiazepines, the compound does not bind to the benzodiazepine binding site of the γ-aminobutyric acid receptor and its psychopharmacological profile differs from such compounds. In addition to anxiolytic properties, antipsychotic effects are reported. We now show that tofisopam, 50 mg/kg intraperitoneally (i.p.), administered in parallel to repeated doses of dizocilpine 0.2 mg/kg i.p. can ameliorate dizocilpine-induced prolongation of immobility, which is considered to be a model of negative symptoms of psychosis. We further show that tofisopam acts as an isoenzyme-selective inhibitor of phosphodiesterases (PDEs) with highest affinity to PDE-4A1 (0.42 μM) followed by PDE-10A1 (0.92 μM), PDE-3 (1.98 μM) and PDE-2A3 (2.11 μM). The data indicate that tofisopam is an interesting candidate for the adjuvant treatment of psychosis with focus on negative symptoms. Combined partial inhibition of PDE-4 and PDE-10 as well as PDE-2 may be the underlying mechanism to this activity. Due to the good safety profile of tofisopam as evident from long-term use of this agent in patients, it may be concluded that dual or triple inhibition of PDE isoenzymes with additive or synergistic effects may be an interesting approach to pharmacological activity, resulting in active compounds with beneficial safety profile. Dose-limiting side effects such as emesis induced by selective inhibition of PDE-4 may be prevented by such strategies.

Similarities in the behavior and molecular deficits in the frontal cortex between the neurotensin receptor subtype 1 knockout mice and chronic phencyclidine-treated mice: relevance to schizophrenia

Much evidence suggests that targeting the neurotensin (NT) system may provide a novel and promising treatment for schizophrenia. Our recent work shows that: NTS1 knockout (NTS1(-/-)) mice may provide a potential animal model for studying schizophrenia by investigating the effect of deletion NTS1 receptor on amphetamine-induced hyperactivity and neurochemical changes. The data indicate a hyper-dopaminergic state similar to the excessive striatal DA activity reported in schizophrenia. The present study was done to determine if NTS1(-/-) mice also have similar changes in behavior, in prefrontal neurotransmitters, and in protein expression, as observed in wild type (WT) mice treated with the psychotomimetic phencylclidine (PCP), an animal model for schizophrenia. Our results showed many similarities between untreated NTS1(-/-) mice and WT mice chronically treated with PCP (as compared with untreated WT mice): 1) lower PCP-induced locomotor activity; 2) similar avolition-like behavior in forced-swim test and tail suspension test; 3) lower prefrontal glutamate levels; 4) less PCP-induced dopamine release in medial prefrontal cortex (mPFC); and 5) down-regulation of mRNA and protein for DA D(1), DA D(2), and NMDAR2A in mPFC. Therefore, these data strengthen the hypothesis that the NTS1(-/-) mouse is an animal model of schizophrenia, particularly for the dysfunction of the prefrontal cortex. In addition, after chronic PCP administration, the DA D(1) receptor was up-regulated in NTS1(-/-) mice, results which suggest a possible interaction of NTS1/DA D(1) in mPFC contributing to chronic PCP-induced schizophrenia-like signs.

Opposite effect of phencyclidine on activity-regulated cytoskeleton-associated protein (Arc) in juvenile and adult limbic rat brain regions

The psychotomimetic effect of NMDA antagonists such as phencyclidine (PCP) in humans spurred the hypoglutamatergic theory of schizophrenia. This theory is supported by animal studies demonstrating schizophrenia-like behavioral and molecular changes following PCP administration to adult or neonatal animals. However, schizophrenia is believed to develop in part due to neurodevelopmental dysfunction during adolescence. Therefore, the effects of PCP in juvenile animals may better reflect the pathophysiology of schizophrenia. Here, we compare the effect of PCP (5mg/kg/day for 5 days) on activity-regulated cytoskeleton-associated protein (Arc) and parvalbumin mRNA expression in juvenile and adult rats. Arc is a marker for excitatory neurotransmission. Parvalbumin is a marker for GABAergic neurotransmission, known to be reduced in postmortem brains of schizophrenics. PCP reduced parvalbumin mRNA expression in the medial prefrontal cortex (mPFC), ventrolateral orbitofrontal cortex (VLO) and shell of the nucleus accumbens (ACCshell) in both juvenile and adult rats. Contrarily, PCP produced opposite effects on Arc mRNA expression in the mPFC, VLO and ACCshell, leading to decreased expression in juvenile and increased expression in adult rats. The differential effect of PCP in juvenile and adult rats may be caused by the immature functional state of the prefrontal cortex in juvenile rats. These results demonstrate differences between the effects of PCP in juvenile and adult rats. The decrease in Arc mRNA in juvenile rats corresponds best with the proposed "hypofrontality" in schizophrenia, suggesting the merits of using PCP in juvenile animals as a model for schizophrenia, as this would relate better to the typical onset and clinical features of schizophrenia.

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.

Transient hypolocomotion in rats repeatedly exposed to phencyclidine: an appraisal of motor function and motivation

Spontaneous locomotion in rats is reduced about 20 h following phencyclidine (PCP) exposure. Our primary purpose was to test if locomotor irregularities would outlast drug withdrawal and be modulated by a periodic auditory stimulation during or after repeated injections. To circumscribe plausible interpretations, motor coordination and motivation were assessed as well. 10 mg/kg of PCP decreased spontaneous locomotion during the injection period whether or not a sound was presented. Those effects did not persist after a 7-day washout. Motor coordination and motivation to perform a variety of goal-driven conducts in the presence or absence of reinforcement were all unaffected by PCP treatment. The generalized hypolocomotor effects induced by PCP likely resulted from an inability to self-generate behaviors. These deficiencies were apparent in contexts where response production was not clearly specified nor supported, regardless of reward contingency.

Repeated application of ketamine to rats induces changes in the hippocampal expression of parvalbumin, neuronal nitric oxide synthase and cFOS similar to those found in human schizophrenia

Treatment with the phencyclidine derivative ketamine, a non-competitive N-methyl-D-aspartate receptor antagonist and a well known anesthetic, has recently been introduced to mimic schizophrenia in animals. Using rats repeatedly treated with sub-anesthetic doses we demonstrate in the hippocampal formation the cellular distribution patterns of proteins being relevant to the pathogenesis of schizophrenia. Compared with controls an increase in the density of reduced nicotinamide adenine dinucleotide phosphate diaphorase-, neuronal nitric oxide synthase- and cFOS-positive hippocampal interneurons was found, whereas the density of parvalbumin expressing cells was decreased. Our experiments show that repeated injections of sub-anesthetic doses of ketamine induce significant changes in the nitrergic and GABAergic system which, in part, resemble those described in postmortem brains of human schizophrenics indicating that sub-chronic treatment with sub-anesthetic doses of ketamine might be a useful animal model to study schizophrenia.