(+)-MK-801 induced social withdrawal in rats; a model for negative symptoms of schizophrenia

Dissociating the effects of habituation, black walls, buspirone and ethanol on anxiety-like behavioral responses in shoaling zebrafish. A 3D approach to social behavior

Understanding the different patterns of anxiety-like behavioral responses is of great interest for pharmacological and genetic research. Here we report the effects of 3.5-hr habituation, buspirone and ethanol on those responses in shoaling zebrafish (Danio rerio). Since in these experiments we used a container with white walls, the effects of black-vs.-white walls were tested in a separate experiment. An important objective was to determine whether factors unrelated to anxiety played a role in modulating the responses. The anxiety-like behavioral responses studied here are social cohesion, distance from bottom and bottom-dwell time, radial distribution (to study thigmotaxis), transparent-wall preference (to study escape responses), locomotion and freezing. The experimental conditions yielded distinctly different response patterns. Thigmotaxis was the most obvious response to white walls and it was significantly reduced after 3.5-hr habituation. It was not affected by any of the drugs. The reduction of social cohesion after 3.5-hr habituation and in the 0.5% ethanol group was probably the most interesting effect seen in this study. A role of anxiety herein was suggested but could not be established with certainty. Other hypotheses were also discussed. The large increase of distance-from-bottom resulting in swimming close to the water surface, which occurred in both buspirone groups and in the 0.5%-ethanol group, is most likely not an anxiolytic response, because of the discrepancy with the in the literature well-established time-course and the absence of any effect of 3.5-hr habituation or black walls on vertical measures. Finally, locomotion and duration freezing could not be specifically taken as indicators for the state of anxiety and the results concerning transparent-wall preference were not sufficient clear. We conclude that the neuronal and ethological mechanisms underlying the effects of habituation, white-aversion, buspirone and ethanol on anxiety-like behavioral responses are complex and need further exploration.

Metabolomic analysis reveals metabolic disturbance in the cortex and hippocampus of subchronic MK-801 treated rats

Background

Although a number of proteins and genes relevant to schizophrenia have been identified in recent years, few are known about the exact metabolic pathway involved in this disease. Our previous proteomic study has revealed the energy metabolism abnormality in subchronic MK-801 treated rat, a well-established animal model for schizophrenia. This prompted us to further investigate metabolite levels in the same rat model to better delineate the metabolism dysfunctions and provide insights into the pathology of schizophrenia.

Methods

Metabolomics, a high-throughput investigatory strategy developed in recent years, can offer comprehensive metabolite-level insights that complement protein and genetic findings. In this study, we employed a nondestructive metabolomic approach (1H-MAS-NMR) to investigate the metabolic traits in cortex and hippocampus of MK-801 treated rats. Multivariate statistics and ingenuity pathways analyses (IPA) were applied in data processing. The result was further integrated with our previous proteomic findings by IPA analysis to obtain a systematic view on our observations.

Results

Clear distinctions between the MK-801 treated group and the control group in both cortex and hippocampus were found by OPLS-DA models (with R²X = 0.441, Q²Y = 0.413 and R²X = 0.698, Q²Y = 0.677, respectively). The change of a series of metabolites accounted for the separation, such as glutamate, glutamine, citrate and succinate. Most of these metabolites fell in a pathway characterized by down-regulated glutamate synthesis and disturbed Krebs cycle. IPA analysis further confirmed the involvement of energy metabolism abnormality induced by MK-801 treatment.

Conclusions

Our metabolomics findings reveal systematic changes in pathways of glutamate metabolism and Krebs cycle in the MK-801 treated rats’ cortex and hippocampus, which confirmed and improved our previous proteomic observation and served as a valuable reference to the etiology research of schizophrenia.

The competitive NMDA receptor antagonist CPP disrupts cocaine-induced conditioned place preference, but spares behavioral sensitization

Recently, the notion that memory and addiction share similar neural substrates has become widely accepted. N-methyl-d-aspartate receptors (NMDAR) are the cornerstones of synaptic models of memory. The present study examined the effect of the competitive NMDAR antagonist CPP on the induction of behavioral sensitization and conditioned place preference to cocaine. Conditioned place preference is an associative memory model of drug seeking, while sensitization is a non-associative model of the transition from casual to compulsive use. There were three principal findings: (1) co-administration of CPP and cocaine altered the acute response to cocaine, suggesting a direct interaction between the two drugs; (2) NMDAR antagonism had no effect on behavioral sensitization; and (3) NMDAR antagonism abolished conditioned place preference. A review of prior evidence supporting a role for NMDARs in sensitization suggests that NMDAR antagonists directly interfere with cocaine's psychostimulant effects, and this interaction could be misinterpreted as a disruption of sensitization. Finally, we suggest that addiction recruits multiple kinds of plasticity, with sensitization recruiting NMDAR-independent mechanisms.

Cannabidiol and clozapine reverse MK-801-induced deficits in social interaction and hyperactivity in Sprague-Dawley rats

Recently, a novel paradigm has been designed to assess social investigative behaviour in pairs of Sprague-Dawley rats, which involves physical separation whilst ensuring they are able to maintain contact through other social cues. We have modified this set-up in order to assess not just social behaviour but also locomotor activity of the rats. Results showed that the MK-801- (0.3 mg/kg) treated rats displayed reduced social investigative behaviour, hyperactivity as well as reduced attention span. Pretreatment with the phytocannabinoid cannabidiol (3 mg/kg) not only normalised social investigative behaviour but increased it beyond control levels. Pretreatment with clozapine (1, 3 mg/kg) also normalised social investigative behaviour. Both cannabidiol and clozapine inhibited MK-801-induced hyperactivity. However, there were no effects of pretreatment on impairments to attention span. Our findings reinforce several aspects of the validity of the MK-801-induced model of social withdrawal and hyperactivity and also support the use of this novel set-up for further investigations to assess the antipsychotic potential of novel compounds.

A two-hit model: behavioural investigation of the effect of combined neonatal MK-801 administration and isolation rearing in the rat

This study combined two neurodevelopmental manipulations, neonatal MK-801 treatment and isolation rearing, to produce a 'two-hit' model and determine whether two hits induce a more robust behavioural phenotype of an animal model of aspects of schizophrenia compared with individual manipulations alone. The effect of clozapine was also assessed. Male Sprague-Dawley rats received 0.2 mg/kg MK-801 or saline intraperitoneally (i.p.) once daily on postnatal days (PNDs) 7-10 and were assigned to group or isolation rearing at weaning (PND 21). From PND 77, they received a vehicle or 5 mg/kg clozapine (i.p.) treatment regimen and were subjected to three prepulse inhibition (PPI) tests, a locomotor activity assessment and a novel object recognition task. MK-801-treated rats reared in isolation displayed robust PPI disruptions which were consistently manifested in all three tests. PPI deficits were also detected in saline-treated rats reared in isolation but not in all tests. Only the two-hit rats demonstrated hyperlocomotion and impaired object recognition memory. Clozapine restored PPI anomalies in the two-hit rats. The two-hit model showed greater psychotic-like effects than either neonatal MK-801 or isolation rearing alone. The preliminary predictive validity shown with clozapine suggests this model may be useful for predicting the efficacy of putative antipsychotics.

Variable prenatal stress results in impairments of sustained attention and inhibitory response control in a 5-choice serial reaction time task in rats

Rats repeatedly exposed to variable prenatal stress (PNS) exhibit schizophrenia-like behavioral signs such as social withdrawal, elevations in amphetamine-induced locomotor activity, deficits in sensory-motor gating, as well as impairments in memory-related task performance. However, to date there have been no studies designed to test the hypothesis that variable PNS would lead to disruptions in sustained attention and inhibitory response control (i.e., symptoms also commonly observed in schizophrenia and other neuropsychiatric disorders such as attention-deficit hyperactivity disorder). In the current study, the effects of variable PNS in rats were evaluated in fixed and variable stimulus duration (VSD) as well as variable intertrial interval (VITI) versions of a 5-choice serial reaction time task (5C-SRTT). In a separate series of experiments, the glutamate (N-methyl-d-aspartate [NMDA]) antagonist, MK-801 (0.025-0.05 mg/kg), and the norepinephrine reuptake inhibitor, atomoxetine (0.30-3.0mg/kg), were administered acutely to assess the sensitivity of PNS subjects to glutamatergic and noradrenergic manipulations. The results indicated that exposure to variable PNS significantly impaired accuracy in the VSD version of the 5C-SRTT and increased premature and timeout responses in the VITI version. In addition, both doses of MK-801 impaired accuracy, increased premature and timeout responses in PNS, but not control subjects. In contrast, atomoxetine decreased premature and timeout responses in both PNS and control subjects in the VITI version of the task and improved accuracy in the PNS subjects. The results suggest that exposure to variable PNS in rats results in impairments of sustained attention and inhibitory response control and that these deficits can be exacerbated by NMDA antagonism and improved by a norepinephrine uptake inhibitor. Collectively, these data further support the premise that variable PNS in rats is a valid model system for the study of neuropsychiatric disorders and their treatment.

NMDA receptor hypofunction induces dysfunctions of energy metabolism and semaphorin signaling in rats: a synaptic proteome study

There is considerable evidence to suggest that aberrations of synapse connectivity contribute to the pathophysiology of schizophrenia and that N-methyl-D-aspartate (NMDA) receptor-mediated glutamate transmission is especially important. Administration of MK-801 ([+]-5-methyl-10, 11-dihydro-5H-dibenzo-[a, d]-cycloheptene-5, 10-iminehydrogenmaleate) induces hypofunction of NMDA receptors in rats, which are widely used as a model for schizophrenia. We investigated synaptosomal proteome expression profiling of the cerebral cortex of MK-801-treated Sprague-Dawley rats using the 2-dimensional difference gel electrophoresis method, and 49 differentially expression proteins were successfully identified using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight/Time-of-Flight mass spectrometry. We carried out a literature search for further confirmation of subsynaptic locations and to explore the relevance to the diseases of differentially expressed proteins. Ingenuity Pathways Analysis (IPA) was used to further examine the underlying relationship between the changed proteins. The network encompassing "cell morphology, cell-to-cell signaling and interaction, nervous system development and function" was found to be significantly altered in the MK-801-treated rats. "Energy metabolism" and "semaphorin signaling in neurons" are the most significant IPA canonical pathways to be affected by MK-801 treatment. Using western blots, we confirmed the differential expression of Camk2a, Crmp2, Crmp5, Dnm1, and Ndufs3 in both synaptosome proteins and total proteins in the cerebral cortex of the rats. Our study identified the change and/or response of the central nervous transmission system under the stress of NMDA hypofunction, underlining the importance of the synaptic function in schizophrenia.

Developmental vitamin D deficiency alters MK-801-induced behaviours in adult offspring

RATIONALE

Developmental vitamin D (DVD) deficiency is a candidate risk factor for developing schizophrenia in humans. In rodents DVD deficiency induces subtle changes in the way the brain develops. This early developmental insult leads to select behavioural changes in the adult, such as an enhanced response to amphetamine-induced locomotion in female DVD-deficient rats but not in male DVD-deficient rats and an enhanced locomotor response to the N-methyl-D: -aspartate (NMDA) receptor antagonist, MK-801, in male DVD-deficient rats. However, the response to MK-801-induced locomotion in female DVD-deficient rats is unknown. Therefore, the aim of the current study was to further examine this behavioural finding in male and female rats and assess NMDA receptor density.

METHODS

DVD-deficient Sprague Dawley rats were assessed for locomotion, ataxia, acoustic startle response (ASR) and prepulse inhibition (PPI) of the ASR to multiple doses of MK-801. The NMDA receptor density in relevant brain regions was assessed in a drug-naive cohort.

RESULTS

DVD deficiency increased locomotion in response to MK-801 in both sexes. DVD-deficient rats also showed an enhanced ASR compared with control rats, but PPI was normal. Moreover, DVD deficiency decreased NMDA receptor density in the caudate putamen of both sexes.

CONCLUSIONS

These results suggest that a transient prenatal vitamin D deficiency has a long-lasting effect on NMDA-mediated signalling in the rodent brain and may be a plausible candidate risk factor for schizophrenia and other neuropsychiatric disorders.

[123I]Epidepride neuroimaging of dopamine D2/D3 receptor in chronic MK-801-induced rat schizophrenia model

PURPOSE

[(123)I]Epidepride is a radio-tracer with very high affinity for dopamine D(2)/D(3) receptors in brain. The importance of alteration in dopamine D(2)/D(3) receptor binding condition has been wildly verified in schizophrenia. In the present study we set up a rat schizophrenia model by chronic injection of a non-competitive NMDA receptor antagonist, MK-801, to examine if [(123)I]epidepride could be used to evaluate the alterations of dopamine D(2)/D(3) receptor binding condition in specific brain regions.

METHOD

Rats were given repeated injection of MK-801 (dissolved in saline, 0.3mg/kg) or saline for 1month. Afterwards, total distance traveled (cm) and social interaction changes were recorded. Radiochemical purity of [(123)I]epidepride was analyzed by Radio-Thin-Layer Chromatography (chloroform: methanol, 9:1, v/v) and [(123)I]epidepride neuroimages were obtained by ex vivo autoradiography and small animal SPECT/CT. Data obtained were then analyzed to determine the changes of specific binding ratio.

RESULT

Chronic MK-801 treatment for a month caused significantly increased local motor activity and induced an inhibition of social interaction. As shown in [(123)I]epidepride ex vivo autoradiographs, MK-801 induced a decrease of specific binding ratio in the striatum (24.01%), hypothalamus (35.43%), midbrain (41.73%) and substantia nigra (37.93%). In addition, [(123)I]epidepride small animal SPECT/CT neuroimaging was performed in the striatum and midbrain. There were statistically significant decreases in specific binding ratio in both the striatum (P<.01) and midbrain (P<.05) between the saline and MK-801 group.

CONCLUSION

These results suggest that [(123)I]epidepride is a useful radio-tracer to reveal the alterations of dopamine D(2)/D(3) receptor binding in a rat schizophrenia model and is also helpful to evaluate therapeutic effects of schizophrenia in the future.

Post-weaning social isolation and subchronic NMDA glutamate receptor blockade: effects on locomotor activity and GABA signaling in the rat suggest independent mechanisms

Animal models of schizophrenia symptoms include administration of noncompetitive N-methyl-d-aspartate (NMDA) glutamate receptor antagonists, such as MK-801, and post-weaning social isolation (SI). We tested the hypothesis that a "double-hit" model, in which MK-801 administration during adulthood [post-natal day (P) 56-62] and SI are combined, produces greater behavioral and neurochemical effects than either insult alone. Rats obtained at weaning (P21) were either SI (n=21) or group housed (n=16) for the duration of the experiment. Subgroups received subchronic treatment with MK-801 (0.5 mg/kg i.p., 2 times daily for 7 days) or saline injections from P56-62. At P70, all groups were tested for locomotor activity and subsequently sacrificed to assess GAT-1 activity and GABA(A) receptor expression in the frontal cortex and hippocampus. SI resulted in increased locomotor activity, GAT-1 activity in frontal cortex and hippocampus and GABA(A) receptor expression in the frontal cortex; MK-801 increased GABA(A) receptor expression in the hippocampus. Activity changes were correlated with changes in hippocampal GAT-1 and frontocortical GABA(A) receptor number. There was no evidence that the double-hit produced a greater effect. Increased GAT-1 activity may be associated with suppression of GABA-mediated inhibitory synaptic transmission and increased GABA(A) receptor expression may be a compensatory response to decreased availability of GABA. Results suggest that SI and subchronic MK-801 may act through independent mechanisms.

5-HT2A/C receptors mediate the antipsychotic-like effects of alstonine

The purpose of this study was to determine the effects of alstonine, an indole alkaloid with putative antipsychotic effects, on working memory by using the step-down inhibitory avoidance paradigm and MK801-induced working memory deficits in mice. Additionally, the role of serotonin 5-HT2A/C receptors in the effects of alstonine on mouse models associated with positive (MK801-induced hyperlocomotion), negative (MK801-induced social interaction deficit), and cognitive (MK801-induced working memory deficit) schizophrenia symptoms was examined. Treatment with alstonine was able to prevent MK801-induced working memory deficit, indicating its potential benefit for cognitive deficits now seen as a core symptom in the disease. Corroborating previously reported data, alstonine was also effective in counteracting MK801-induced hyperlocomotion and social interaction deficit. Ritanserin, a 5-HT2A/C receptor antagonist, prevented alstonine's effects on these three behavioral parameters. This study presents additional evidence that 5-HT2A/C receptors are central to the antipsychotic-like effects of alstonine, consistently seen in mouse models relevant to the three dimensions of schizophrenia symptoms.

The nicotine metabolite, cotinine, attenuates glutamate (NMDA) antagonist-related effects on the performance of the five choice serial reaction time task (5C-SRTT) in rats

Cotinine, the most predominant metabolite of nicotine in mammalian species, has a pharmacological half-life that greatly exceeds its precursor. However, until recently, relatively few studies had been conducted to systematically characterize the behavioral pharmacology of cotinine. Our previous work indicated that cotinine improves prepulse inhibition of the auditory startle response in rats in pharmacological impairment models and that it improves working memory in non-human primates. Here we tested the hypothesis that cotinine improves sustained attention in rats and attenuates behavioral alterations induced by the glutamate (NMDA) antagonist MK-801. The effects of acute subcutaneous (dose range 0.03-10.0 mg/kg) and chronic oral administration (2.0 mg/kg/day in drinking water) of cotinine were evaluated in fixed and variable stimulus duration (VSD) as well as variable intertrial interval (VITI) versions of a five choice serial reaction time task (5C-SRTT). The results indicated only subtle effects of acute cotinine (administered alone) on performance of the 5C-SRTT (e.g., decreases in timeout responses). However, depending on dose, acute treatment with cotinine attenuated MK-801-related impairments in accuracy and elevations in timeout responses, and it increased the number of completed trials. Moreover, chronic cotinine attenuated MK-801-related impairments in accuracy and it reduced premature and timeout responses when the demands of the task were increased (i.e., by presenting VSDs or VITIs in addition to administering MK-801). These data suggest that cotinine may represent a prototype for compounds that have therapeutic potential for neuropsychiatric disorders (i.e., by improving sustained attention and decreasing impulsive and compulsive behaviors), especially those characterized by glutamate receptor alterations.

Consequences of early life MK-801 administration: long-term behavioural effects and relevance to schizophrenia research

Animal models contribute significantly to advancing the understanding of schizophrenia neurobiology, in addition to being an important tool for the screening of antipsychotic potential of new compounds. However, the entire spectrum or all the symptoms manifested in schizophrenia cannot be straightforwardly reproduced in animals due to the complexity of the disorder, difference in mental capacities and behaviours, and the ability to quantify or measure the changes. Blockade of the NMDA receptor by the use of MK-801, a non-competitive NMDA receptor antagonist, during the early postnatal period has been proposed to be an experimental model which induces behavioural changes that mimic several aspects of the disorder. The long term behavioural profile arising from this early life manipulation is reviewed herein, with a specific focus on behaviours relevant to a schizophrenia-like condition. Some of the reported neurochemical changes are also compiled. Although this method may be suitable to model some aspects of schizophrenia in rodents, there are unmet areas which need to be addressed, notably the characterisation of its predictive value.

Exposure to novel environment is characterized by an interaction of D1/NMDA receptors underlined by phosphorylation of the NMDA and AMPA receptor subunits and activation of ERK1/2 signaling, leading to epigenetic changes and gene expression in rat hippocampus

Interactions between dopamine and glutamate receptors are essential for prefrontal cortical (PFC) and hippocampal cognitive functions. The hippocampus has been identified as a detector of a novel stimulus, where an association between incoming information and stored memories takes place. Further to our previous results which showed a strong synergistic interaction of dopamine D1 and glutamate NMDA receptors, the present study is going to investigate the functional status of that interaction in rats, following their exposure to a novel environment. Our results showed that the "spatial" novelty induced in rat hippocampus and PFC (a) a significant increase in phosphorylation of NMDA and AMPA receptor subunits, as well as a robust phosphorylation/activation of ERK1/2 signaling, which are both dependent on the concomitant stimulation of D1/NMDA receptors and are both abolished by habituation procedure, (b) chromatin remodeling events (phosphorylation-acetylation of histone H3) and (c) an increase in the immediate early genes (IEGs) c-Fos and zif-268 expression in the CA1 region of hippocampus, which is dependent on the co-activation of D1/NMDA and acetylcholine muscarinic receptors. In conclusion, our results clearly show that a strong synergistic interaction of D1/NMDA receptor is required for the novelty-induced phosphorylation of NMDA and AMPA receptor subunits and for the robust activation of ERK1/2 signaling, leading to chromatin remodeling events and the expression of the IEGs c-Fos and zif-268, which are involved in the regulation of synaptic plasticity and memory consolidation.

Alstonine as an antipsychotic: effects on brain amines and metabolic changes

Managing schizophrenia has never been a trivial matter. Furthermore, while classical antipsychotics induce extrapyramidal side effects and hyperprolactinaemia, atypical antipsychotics lead to diabetes, hyperlipidaemia, and weight gain. Moreover, even with newer drugs, a sizable proportion of patients do not show significant improvement. Alstonine is an indole alkaloid identified as the major component of a plant-based remedy used in Nigeria to treat the mentally ill. Alstonine presents a clear antipsychotic profile in rodents, apparently with differential effects in distinct dopaminergic pathways. The aim of this study was to complement the antipsychotic profile of alstonine, verifying its effects on brain amines in mouse frontal cortex and striatum. Additionally, we examined if alstonine induces some hormonal and metabolic changes common to antipsychotics. HPLC data reveal that alstonine increases serotonergic transmission and increases intraneuronal dopamine catabolism. In relation to possible side effects, preliminary data suggest that alstonine does not affect prolactin levels, does not induce gains in body weight, but prevents the expected fasting-induced decrease in glucose levels. Overall, this study reinforces the proposal that alstonine is a potential innovative antipsychotic, and that a comprehensive understanding of its neurochemical basis may open new avenues to developing newer antipsychotic medications.

Antipsychotic drugs reverse MK-801-induced cognitive and social interaction deficits in zebrafish (Danio rerio)

Schizophrenia is a severe mental illness characterized by positive and negative symptoms and cognitive deficits. Reduction of glutamatergic neurotransmission by NMDA receptor antagonists mimics symptoms of schizophrenia. Modeling social interaction and cognitive impairment in animals can be of great benefit in the effort to develop novel treatments for negative and cognitive symptoms of schizophrenia. Studies have demonstrated that these behavioral changes are, in some cases, sensitive to remediation by antipsychotic drugs. The zebrafish has been proposed as a candidate to study the in vivo effects of several drugs and to discover new pharmacological targets. In the current study we investigated the ability of antipsychotic drugs to reverse schizophrenia-like symptoms produced by the NMDA receptor antagonist MK-801. Results showed that MK-801 (5μM) given pre-training hindered memory formation while both atypical antipsychotics sulpiride (250μM) and olanzapine (50μM) improved MK-801-induced amnesia. The same change was observed in the social interaction task, where atypical antipsychotics reversed the MK-801-induced social interaction deficit whereas the typical antipsychotic haloperidol (9μM) was ineffective to reverse those behavioral deficits. Therefore, MK-801-treated zebrafish showed some behavioral features observed in schizophrenia, such as cognitive and social interaction deficits, which were reverted by current available atypical drugs.

Intramolecular alkene carboamination reactions for the synthesis of enantiomerically enriched tropane derivatives

The synthesis of tropane derivatives via intramolecular Pd-catalyzed alkene difunctionalization reactions is described. Enantiopure N-aryl-γ-aminoalkenes bearing an aryl or alkenyl halide adjacent to the amino group were converted to benzo- or cycloalkenyl-fused tropane products in good yield and with no loss of enantiopurity.

Proteome analyses of cultured astrocytes treated with MK-801 and clozapine: similarities with schizophrenia

On the basis of impaired glutamatergic transmission and the potential role of astrocytes in schizophrenia, we treated cultured astrocytes with MK-801, an NMDA-receptor antagonist, to investigate whether the resulting proteome changes are similar to those we found in our earlier proteome analysis of schizophrenia human brain tissue as well as to better comprehend the role of astrocytes in the disorder. Indeed, there are similarities. Furthermore, to verify the efficacy of clozapine and its effect over the proteome, we treated MK-801-treated astrocytes with clozapine. Interestingly, clozapine reversed protein changes induced by MK-801. The treatment of cell cultures with neural transmission agonists and antagonists might provide useful insights about psychiatric disorders.

Altered 13C glucose metabolism in the cortico-striato-thalamo-cortical loop in the MK-801 rat model of schizophrenia

Using a modified MK-801 (dizocilpine) N-methyl-D-aspartic acid (NMDA) receptor hypofunction model for schizophrenia, we analyzed glycolysis, as well as glutamatergic, GABAergic, and monoaminergic neurotransmitter synthesis and degradation. Rats received an injection of MK-801 daily for 6 days and on day 6, they also received an injection of [1-(13)C]glucose. Extracts of frontal cortex (FCX), parietal and temporal cortex (PTCX), thalamus, striatum, nucleus accumbens (NAc), and hippocampus were analyzed using (13)C nuclear magnetic resonance spectroscopy, high-performance liquid chromatography, and gas chromatography-mass spectrometry. A pronounced reduction in glycolysis was found only in PTCX, in which (13)C labeling of glucose, lactate, and alanine was decreased. (13)C enrichment in lactate, however, was reduced in all areas investigated. The largest reductions in glutamate labeling were detected in FCX and PTCX, whereas in hippocampus, striatum, and Nac, (13)C labeling of glutamate was only slightly but significantly reduced. The thalamus was the only region with unaffected glutamate labeling. γ-Aminobutyric acid (GABA) labeling was reduced in all areas, but most significantly in FCX. Glutamine and aspartate labeling was unchanged. Mitochondrial metabolites were also affected. Fumarate labeling was reduced in FCX and thalamus, whereas malate labeling was reduced in FCX, PTCX, striatum, and NAc. Dopamine turnover was decreased in FCX and thalamus, whereas that of serotonin was unchanged in all regions. In conclusion, neurotransmitter metabolism in the cortico-striato-thalamo-cortical loop is severely impaired in the MK-801 (dizocilpine) NMDA receptor hypofunction animal model for schizophrenia.

PAOPA, a potent analogue of Pro-Leu-glycinamide and allosteric modulator of the dopamine D2 receptor, prevents NMDA receptor antagonist (MK-801)-induced deficits in social interaction in the rat: implications for the treatment of negative symptoms in schizophrenia

The aim of this study was to investigate whether a potent analogue of the endogenous brain peptide l-prolyl-l-leucyl-glycinamide (PLG), (3(R)-[(2(S)-pyrrolidinylcarbonyl)amino]-2-oxo-1-pyrrolidineacetamide (PAOPA), can prevent the induction of social withdrawal caused by sub-chronic treatment with the non-competitive NMDA (N-methyl-l-aspartate) receptor antagonist, MK-801. Results indicate that MK-801 (0.5 mg/kg) significantly decreased social interaction following sub-chronic treatment (7 days). Treatment with PAOPA (1 mg/kg) blocked the effects of MK-801, and increased the amount of time spent in social interaction in comparison to control animals. These results provide evidence for the development of peptidomimetic compounds for the treatment of social withdrawal and related negative symptoms associated with schizophrenia.

Animal models of cognitive dysfunction and negative symptoms of schizophrenia: focus on NMDA receptor antagonism

Cognitive deficits in schizophrenia remain an unmet clinical need. Improved understanding of the neuro- and psychopathology of these deficits depends on the availability of carefully validated animal models which will assist the development of novel therapies. There is much evidence that at least some of the pathology and symptomatology (particularly cognitive and negative symptoms) of schizophrenia results from a dysfunction of the glutamatergic system which may be modelled in animals through the use of NMDA receptor antagonists. The current review examines the validity of this model in rodents. We review the ability of acute and sub-chronic treatment with three non-competitive NMDA antagonists; phencyclidine (PCP), ketamine and MK801 (dizocilpine) to produce cognitive deficits of relevance to schizophrenia in rodents and their subsequent reversal by first- and second-generation antipsychotic drugs. Effects of NMDA receptor antagonists on the performance of rodents in behavioural tests assessing the various domains of cognition and negative symptoms are examined: novel object recognition for visual memory, reversal learning and attentional set shifting for problem solving and reasoning, 5-Choice Serial Reaction Time for attention and speed of processing; in addition to effects on social behaviour and neuropathology. The evidence strongly supports the use of NMDA receptor antagonists to model cognitive deficit and negative symptoms of schizophrenia as well as certain pathological disturbances seen in the illness. This will facilitate the evaluation of much-needed novel pharmacological agents for improved therapy of cognitive deficits and negative symptoms in schizophrenia.

A follow-up study: acute behavioural effects of Delta(9)-THC in female heterozygous neuregulin 1 transmembrane domain mutant mice

RATIONALE

Heavy cannabis use is linked with an increased risk for schizophrenia. We showed previously that male heterozygous neuregulin 1 transmembrane domain (Nrg1 HET) mice are more sensitive to some effects of the psychotropic cannabis constituent Delta(9)-tetrahydrocannabinol (THC). We report data from a follow-up study in female Nrg1 HET mice, investigating THC effects on behaviours with some relevance to schizophrenia.

METHODS

Mice were injected with THC (0, 5 or 10 mg/kg i.p.) 30 min before a test battery: open field, elevated plus maze, novel object recognition (set 1) or light-dark, social interaction (SI) and prepulse inhibition (PPI 1: variable interstimulus interval (ISI); set 2). Another set (set 3) was injected with the same doses of THC before a fixed interstimulus interval PPI test (PPI 2).

RESULTS

Female Nrg1 HETs displayed the hallmark increased locomotor activity at 5 months and anxiolytic-like behaviour in the open field at 3 and 5 months. THC decreased locomotor activity in both genotypes. THC selectively reduced some SI behaviours in WT mice. Baseline PPI was enhanced in mutants under a variable ISI, while THC had no effect on PPI using either protocol.

CONCLUSIONS

This study reports novel findings on the baseline PPI profile and resistance to THC-induced social withdrawal in female Nrg1 HET mice. This is the first description of THC effects in females of this mouse model and suggests that the transmembrane domain Nrg1 mutation does not appear to have a severe impact on the behavioural sensitivity to THC in female mice.

A behavioural comparison of acute and chronic Delta9-tetrahydrocannabinol and cannabidiol in C57BL/6JArc mice

Cannabis contains over 70 unique compounds and its abuse is linked to an increased risk of developing schizophrenia. The behavioural profiles of the psychotropic cannabis constituent Delta9-tetrahydrocannabinol (Delta9-THC) and the non-psychotomimetic constituent cannabidiol (CBD) were investigated with a battery of behavioural tests relevant to anxiety and positive, negative and cognitive symptoms of schizophrenia. Male adult C57BL/6JArc mice were given 21 daily intraperitoneal injections of vehicle, Delta9-THC (0.3, 1, 3 or 10 mg/kg) or CBD (1, 5, 10 or 50 mg/kg). Delta9-THC produced the classic cannabinoid CB1 receptor-mediated tetrad of hypolocomotion, analgesia, catalepsy and hypothermia while CBD had modest hyperthermic effects. While sedative at this dose, Delta9-THC (10 mg/kg) produced locomotor-independent anxiogenic effects in the open-field and light-dark tests. Chronic CBD produced moderate anxiolytic-like effects in the open-field test at 50 mg/kg and in the light-dark test at a low dose (1 mg/kg). Acute and chronic Delta9-THC (10 mg/kg) decreased the startle response while CBD had no effect. Prepulse inhibition was increased by acute treatment with Delta9-THC (0.3, 3 and 10 mg/kg) or CBD (1, 5 and 50 mg/kg) and by chronic CBD (1 mg/kg). Chronic CBD (50 mg/kg) attenuated dexamphetamine (5 mg/kg)-induced hyperlocomotion, suggesting an antipsychotic-like action for this cannabinoid. Chronic Delta9-THC decreased locomotor activity before and after dexamphetamine administration suggesting functional antagonism of the locomotor stimulant effect. These data provide the first evidence of anxiolytic- and antipsychotic-like effects of chronic but not acute CBD in C57BL/6JArc mice, extending findings from acute studies in other inbred mouse strains and rats.

Effects of inhaled Linalool in anxiety, social interaction and aggressive behavior in mice

Aromatherapy uses essential oils (EOs) for several medical purposes, including relaxation. The association between the use of aromas and a decrease in anxiety could be a valuable instrument in managing anxiety in an ever increasing anxiogenic daily life style. Linalool is a monoterpene commonly found as the major volatile component of EOs in several aromatic plant species. Adding to previously reported sedative effects of inhaled linalool, the aim of this study was to investigate the effects of inhaled linalool on anxiety, aggressiveness and social interaction in mice. Additionally, we investigated the effects of inhaled linalool on the acquisition phase of a step-down memory task in mice. Inhaled linalool showed anxiolytic properties in the light/dark test, increased social interaction and decreased aggressive behavior; impaired memory was only seen the higher dose of linalool. These results strengthen the suggestion that inhaling linalool rich essential oils can be useful as a mean to attain relaxation and counteract anxiety.

Efficacy of 3,5-dibromo-L-phenylalanine in rat models of stroke, seizures and sensorimotor gating deficit

BACKGROUND AND PURPOSE

Abnormal glutamatergic activity is implicated in neurologic and neuropsychiatric disorders. Selective glutamate receptor antagonists were highly effective in animal models of stroke and seizures but failed in further clinical development because of serious side effects, including an almost complete set of symptoms of schizophrenia. Therefore, the novel polyvalent glutamatergic agent 3,5-dibromo-L-phenylalanine (3,5-DBr-L-Phe) was studied in rat models of stroke, seizures and sensorimotor gating deficit.

EXPERIMENTAL APPROACH

3,5-DBr-L-Phe was administered intraperitoneally as three boluses after intracerebral injection of endothelin-1 (ET-1) adjacent to the middle cerebral artery to cause brain injury (a model of stroke). 3,5-DBr-L-Phe was also given as a single bolus prior to pentylenetetrazole (PTZ) injection to induce seizures or prior to the administration of the N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine (MK-801) to cause disruption of prepulse inhibition (PPI) of startle (sensorimotor gating deficit).

KEY RESULTS

Brain damage caused by ET-1 was reduced by 52%, which is comparable with the effects of MK-801 in this model as reported by others. 3,5-DBr-L-Phe significantly reduced seizures induced by PTZ without the significant effects on arterial blood pressure and heart rate normally caused by NMDA antagonists. 3,5-DBr-L-Phe prevented the disruption of PPI measured 3 days after the administration of ET-1. 3,5-DBr-L-Phe also eliminated sensorimotor gating deficit caused by MK-801.

CONCLUSION AND IMPLICATIONS

The pharmacological profile of 3,5-DBr-L-Phe might be beneficial not only for developing a therapy for the neurological and cognitive symptoms of stroke and seizures but also for some neuropsychiatric disorders.

Preclinical behavioral models for predicting antipsychotic activity

Schizophrenia is a major psychiatric disease that is characterized by three distinct symptom domains: positive symptoms, negative symptoms, and cognitive impairment. Additionally, treatment with classical antipsychotic medication can be accompanied by important side effects that involve extrapyramidal symptoms (EPS). The discovery of clozapine in the 1970s, which is efficacious in all three symptom domains and has a reduced propensity to induce EPS, has driven research for new antipsychotic agents with a wider spectrum of activity and a lower propensity to induce EPS. The following chapter reviews existing behavioral procedures in animals for their ability to predict compound efficacy against schizophrenia symptoms and liability to induce EPS. Rodent models of positive symptoms include procedures related to hyperfunction in central dopamine and serotonin (5-hydroxytryptamine) systems and hypofunction of central glutamatergic (N-methyl-d-aspartate) neurotransmission. Procedures for evaluating negative symptoms include rodent models of anhedonia, affective flattening, and diminished social interaction. Cognitive deficits can be assessed in rodent models of attention (prepulse inhibition (PPI), latent inhibition) and of learning and memory (passive avoidance, object and social recognition, Morris water maze, and operant-delayed alternation). The relevance of the conditioned avoidance response (CAR) is also discussed. A final section reviews animal procedures for assessing EPS liability, in particular parkinsonism (catalepsy), acute dystonia (purposeless chewing in rodents, dystonia in monkeys), akathisia (defecation in rodents), and tardive dyskinesia (long-term antipsychotic treatment in rodents and monkeys).

Phenotypic characterization of mice heterozygous for a null mutation of glutamate carboxypeptidase II

Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system. Disturbed glutamate signaling resulting in hypofunction of N-methyl-D-aspartate receptors (NMDAR) has been implicated in the pathophysiology of schizophrenia. Glutamate Carboxypeptidase II (GCP II) hydrolyzes N-acetyl-alpha L-aspartyl-L-glutamate (NAAG) into glutamate and N-acetyl-aspartate. NAAG is a neuropeptide that is an NMDAR antagonist as well as an agonist for the metabotropic glutamate receptor-3 (mGluR3), which inhibits glutamate release. The aggregate effect of NAAG is thus to attenuate NMDAR activation. To manipulate the expression of GCP II, LoxP sites were inserted flanking exons 1 and 2, which were excised by crossing with a Cre-expressing mouse. The mice heterozygous for this deletion showed a 50% reduction in the expression level of protein and functional activity of GCP II in brain samples. Heterozygous mutant crosses did not yield any homozygous null animals at birth or as embryos (N > 200 live births and fetuses). These data are consistent with the previous report that GCP II homozygous mutant mice generated by removing exons 9 and 10 of GCP II gene were embryonically lethal and confirm our hypothesis that GCP II plays an essential role early in embryonic development. Heterozygous mice, however, developed normally to adulthood and exhibited increased locomotor activity, reduced social interaction, and a subtle cognitive deficit in working memory.

Deficient NRG1-ERBB signaling alters social approach: relevance to genetic mouse models of schizophrenia

Growth factor Neuregulin 1 (NRG1) plays an essential role in development and organization of the cerebral cortex. NRG1 and its receptors, ERBB3 and ERBB4, have been implicated in genetic susceptibility for schizophrenia. Disease symptoms include asociality and altered social interaction. To investigate the role of NRG1-ERBB signaling in social behavior, mice heterozygous for an Nrg1 null allele (Nrg1+/−), and mice with conditional ablation of Erbb3 or Erbb4 in the central nervous system, were evaluated for sociability and social novelty preference in a three-chambered choice task. Results showed that deficiencies in NRG1 or ERBB3 significantly enhanced sociability. All of the mutant groups demonstrated a lack of social novelty preference, in contrast to their respective wild-type controls. Effects of NRG1, ERBB3, or ERBB4 deficiency on social behavior could not be attributed to general changes in anxiety-like behavior, activity, or loss of olfactory ability. Nrg1+/− pups did not exhibit changes in isolation-induced ultrasonic vocalizations, a measure of emotional reactivity. Overall, these findings provide evidence that social behavior is mediated by NRG1-ERBB signaling.

Low dose MK-801 reduces social investigation in mice

To characterize MK-801's effect on social behavior in mice, we examined adult male ICR mice for interaction with companion mice (juvenile male). Test mice were injected with either saline or MK-801 (0.1 mg/kg), and were tested 30 min later for their social behavior during a 5-min session. A second encounter took place 30 min later, with either a familiar companion mouse (the same as in the initial encounter) or a novel mouse. In saline controls, second encounter with a familiar companion mouse showed reduced social investigative behaviors (anogenital sniffing and staying together), indicating habituation toward a familiar mouse. Second encounter with a novel companion mouse did not show habituation in social investigative behaviors. Pretreatment with MK-801 reduced anogenital sniffing during the first encounter. At the second encounter, these mice displayed non-discriminative habituation of social investigative behaviors, with reduced anogenital sniffing and staying together, regardless of whether the companion mouse was a familiar or a novel one. These results indicate that MK-801 affected exploratory activities of mice, resulting in both reduced social investigative behaviors during first encounter with a companion mouse, and diminished discriminative capacities for a familiar vs. a novel companion mouse during subsequent encounter.

The 5-hydroxytryptamine2A receptor antagonist R-(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenyl)ethyl-4-piperidinemethanol (M100907) attenuates impulsivity after both drug-induced disruption (dizocilpine) and enhancement (antidepressant drugs) of differential-reinforcement-of-low-rate 72-s behavior in the rat

Previous work has suggested that N-methyl-d-aspartate (NMDA) receptor antagonism and 5-hydroxytryptamine (5-HT)(2A) receptor blockade may enhance and attenuate, respectively, certain types of impulsivity mediated by corticothalamostriatal circuits. More specifically, past demonstrations of synergistic "antidepressant-like" effects of a 5-HT(2A) receptor antagonist and fluoxetine on differential-reinforcement-of-low-rate (DRL) 72-s schedule of operant reinforcement may speak to the role of 5-HT(2A) receptor blockade with respect to response inhibition as an important prefrontal cortical executive function relating to motor impulsivity. To examine the dynamic range over which 5-HT(2A) receptor blockade may exert effects on impulsivity, [R-(+)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenyl)ethyl-4-piperidinemethanol] (M100907) was examined both alone and in combination with the psychotomimetic NMDA receptor antagonist dizocilpine [e.g., (-)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate; MK-801] and two different antidepressants, the tricyclic antidepressant desmethylimipramine (DMI) and the monoamine oxidase inhibitor tranylcypromine in rats performing under a DRL 72-s schedule. MK-801 increased the response rate, decreased the number of reinforcers obtained, and exerted a leftward shift in the inter-response time (IRT) distribution as expected. A dose of M100907 that exerted minimal effect on DRL behavior by itself attenuated the psychotomimetic effects of MK-801. Extending previous M100907-fluoxetine observations, addition of a minimally active dose of M100907 to low doses of DMI and tranylcypromine enhanced the antidepressant-like effect of the antidepressants. Therefore, it may be that a tonic excitation of 5-HT(2A) receptors modulates impulsivity and function of corticothalamostriatal circuits over an extensive dynamic range.

The putative antipsychotic alstonine reverses social interaction withdrawal in mice

Negative symptoms of schizophrenia are particularly problematic due to their deleterious impact on a patient's social life. The indol alkaloid alstonine, the major component of traditional remedies used for treating mental illnesses in Nigeria, presents a clear antipsychotic-like profile in mice, as well as anxiolytic properties. Considering that social interaction is the core of negative symptoms, and that anxiolytic drugs can improve social interaction behavior, the aim of this study was to evaluate the effects of alstonine in the social interaction and MK801-induced social withdrawal models in mice. Sub-chronic (but not acute) treatment with alstonine 0.5 mg/kg (but not 1.0 mg/kg) significantly increased social interaction in mice. Moreover, MK801-induced social withdrawal was completely prevented by sulpiride (10 mg/kg) and alstonine 1.0 mg/kg, and partially prevented by alstonine 0.5 mg/kg. The study indicates that alstonine not only increases social interaction in normal mice, but also averts social deficits attributable to negative symptoms of schizophrenia. This study reinforces and complements the antipsychotic-like profile of alstonine, and emphasizes its potential as a drug useful for the management of negative symptoms in schizophrenia.

Interaction between Neuronal Depolarization and MK-801 in SH-SY5Y Cells and the Rat Cortex

OBJECTIVE

The interaction between MK-801, a model of psychosis and KCl-induced depolarization or electroconvulsive shock (ECS), a therapeutic model of electroconvulsive therapy (ECT), was investigated in SH-SY5Y cells and the rat frontal cortex.

METHODS

SH-SY5Y cells were pretreated with 1 microM MK-801 for 15 min, followed by cotreatment with 100 mM KCl for 5 min. MK-801 was reintroduced after the KCl was washed out, and the samples were incubated before harvesting. For the experiments in rats, male Sprague-Dawley rats were treated with MK-801 followed by ECS. Immunoblot analyses of glycogen synthase kinase 3beta (GSK3beta) (Ser9), AKT (Ser473) and extracellular legulated kinase (ERK)1/2 in SH-SY5Y cells and the rat frontal cortex were performed.

RESULTS

KCl-induced neuronal depolarization resulted in the transient dephosphorylation of AKT (Ser473) and GSK3beta (Ser9), followed by increased phosphorylation of the enzymes in SH-SY5Y cells. Cotreatment with MK-801 and KCl inhibited the initial dephosphorylation of AKT and GSK3beta produced by KCl-induced neuronal depolarization. Similarly, ECS resulted in the transient dephosphorylation of AKT (Ser473) and GSK3beta (Ser9), whereas cotreatment with MK-801 inhibited the initial dephosphorylation of AKT (Ser473) and GSK3beta (Ser9) produced by ECS in the rat frontal cortex. No significant interaction was observed between MK-801 and KCl in the dephosphorylation of ERK1/2.

CONCLUSION

These results suggest that an antagonistic interplay between MK-801 and neuronal depolarization by KCl or ECS is involved the regulation of AKT (Ser473) and GSK3beta (Ser9) phosphorylation.

Overview of animal models of schizophrenia

Animal models of schizophrenia may increase the understanding of the neurological abnormalities associated with the disorder and aid in the development of rational pharmacological treatments. Rather than attempting to model the entire syndrome of schizophrenia, a more biologically oriented approach to animal models has been to focus on specific symptoms of schizophrenia that are more objectively measured in the clinical population and more directly translatable to animals (e.g., observables or endophenotypes). This overview focuses on behavioral measures that have been investigated in rodent models of schizophrenia with varying degrees of predictive, etiological, and construct validity. Because of the severity of cognitive deficits in schizophrenia and their resistance to current treatments, there is a need to develop animal models specific to the cognitive symptoms of schizophrenia. In light of this need, this overview discusses rodent models of cognition with relevance to the core cognitive deficits observed in schizophrenia.

Effect of MK-801 on gene expressions in the amygdala of rats

Rodents treated with N-methyl-D-aspartate (NMDA) antagonists have been thought to be an animal model of schizophrenia. In this study, we examined gene expression in the amygdala of rats chronically treated with MK-801, as well as behavioral changes, such as social behavior, in these animals. The social interaction test, a measure of social behavior, and locomotor activity was performed in male Wistar rats injected with MK-801 (0.13 mg/kg i.p.) or saline for 14 days. Changes in mRNA levels were analyzed using a GeneChip microarray system. Real-time quantitative PCR (RT-qPCR) assay was subsequently conducted to confirm the results of the microarray analysis. MK-801 decreased social interaction and increased locomotor activity in rats, consistent with previous reports. We found 23 downregulated genes and 16 upregulated genes, with the gene encoding arginine-vasopressin (AVP) being most downregulated, and that for transthyretin (Ttr) most upregulated. mRNA levels, quantified by RT-qPCR assay, were altered for genes related to neuropeptides (AVP, Sstr2), the arachidonic cascade (Ptgds), myelination (Mobp, Enpp2), neurotrophic factors (Igfbp2), and hormonal milieu (Ttr). Downregulation of the AVP gene in the amygdala of MK-801-treated rats may provide a basis for the ability of AVP-analogues to ameliorate the behavioral disturbances caused by blockade of the NMDA receptor. The results of this study provide an insight into the neural substrates responsible for the generation of psychotic symptoms.

Chronic amphetamine treatment reduces NGF and BDNF in the rat brain

Amphetamines (methamphetamine and d-amphetamine) are dopaminergic and noradrenergic agonists and are highly addictive drugs with neurotoxic effect on the brain. In human subjects, it has also been observed that amphetamine causes psychosis resembling positive symptoms of schizophrenia. Neurotrophins are molecules involved in neuronal survival and plasticity and protect neurons against (BDNF) are the most abundant neurotrophins in the central nervous system (CNS) and are important survival factors for cholinergic and dopaminergic neurons. Interestingly, it has been proposed that deficits in the production or utilization of neurotrophins participate in the pathogenesis of schizophrenia. In this study in order to investigate the mechanism of amphetamine-induced neurotoxicity and further elucidate the role of neurotrophins in the pathogenesis of schizophrenia we administered intraperitoneally d-amphetamine for 8 days to rats and measured the levels of neurotrophins NGF and BDNF in selected brain regions by ELISA. Amphetamine reduced NGF levels in the hippocampus, occipital cortex and hypothalamus and of BDNF in the occipital cortex and hypothalamus. Thus the present data indicate that chronic amphetamine can reduce the levels of NGF and BDNF in selected brain regions. This reduction may account for some of the effects of amphetamine in the CNS neurons and provides evidences for the role of neurotrophins in schizophrenia.

Age-related differential sensitivity to MK-801-induced locomotion and stereotypy in C57BL/6 mice

Psychomotor effects elicited by systemic administration of the noncompetitive NMDA (N-methyl-D-aspartate) receptor antagonist MK-801 (dizocilpine maleate) represent perturbation of glutamatergic pathways, providing an animal model for psychotic symptoms of schizophrenia. Hyperlocomotion and stereotypy are the two main psychomotor behaviors induced by MK-801. This study compared MK-801-induced hyperlocomotion and stereotypy in young (1-month old) and aged mice (12-month old), in order to determine how the aging process may influence these behaviors. The tested MK-801 doses ranged from 0.015 to 1 mg/kg. The data indicated that MK-801 impacted the aged mice more pronouncedly than the young mice, as both hyperlocomotion and stereotypy were increased significantly more in the aged mice relative to the young mice. These results suggest an age-related increase in MK-801 sensitivity in mice.

Oxidative stress in prefrontal cortex of rat exposed to MK-801 and protective effects of CAPE

MK-801 was shown to be one of the most neurotoxic non-competitive NMDA receptor antagonists. It is known that repeated injection of MK-801 was proposed in an animal model in psychosis. The aims of this study are to investigate the contributing effect of oxidative stress in MK-801-induced experimental psychosis model, and to show that prevention of oxidative stress may improve prognosis. Furthermore, there is evidence that oxygen free radicals play an important role in the pathophysiology of schizophrenia. In this study, Wistar Albino rats were divided into three groups: 1st group: Control, 2nd group: MK-801, 3rd group: MK-801+CAPE (Caffeic acid phenethyl ester) group. MK-801 was given intraperitoneally at the dose of 0.5 mg/kg/day for 5 days. CAPE was given to the treatment group while exposed to MK-801. In control group, saline was given intraperitoneally at the same time. After 7 days, rats were killed by decapitation. Prefrontal cortex (PFC) of rats was removed for biochemical and histological analyses. As a result, malondialdehyde (MDA), protein carbonyl (PC), nitric oxide (NO) levels and superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and xanthine oxidase (XO) and adenosine deaminase (AD) enzyme activities were found to be increased significantly in prefrontal cortex (PFC) of MK-801 group (p<0.0001) compared to control group. In CAPE treated rats, prefrontal tissue MDA, PC, NO levels and, GSH-Px, XO, AD enzyme activities were significantly decreased when compared to MK-801 groups (p<0.0001) whereas catalase (CAT) enzyme activity was not changed. Moreover, in the light of microscopic examination of MK-801 groups, a great number of apoptotic cells were observed. CAPE treatment decreased the apoptotic cell count in PFC. The results of this study showed that MK-801-induced neurotoxicity caused oxidative stress in PFC of rats. This experimental study may also provide some evidences for the new treatment strategies with antioxidants in schizophrenia.

The selective mGlu5 receptor antagonist MTEP, similar to NMDA receptor antagonists, induces social isolation in rats

It has repeatedly been shown that uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonists can mimic certain aspects of positive and negative symptoms of schizophrenia in human volunteers and laboratory animals. The purpose of the present study was to expand these findings and to determine whether the selective metabotropic glutamate receptor subtype 5 (mGluR5) antagonist, MTEP (3-[(2-methyl-1,3-thiazol-4-yl)ethynyl]pyridine), could induce similar effects in Wistar rats. First, MTEP (1.0-10.0 mg/kg; intraperitoneally) after acute and subchronic (daily for 5 days) administration as well as the uncompetitive antagonists of the NMDA receptor of either high affinity, phencyclidine (0.5-4.0 mg/kg; subcutaneously (s.c.)) and (+)-MK-801 (0.03-0.25 mg/kg; s.c.), or low-moderate affinity, ketamine (2.0-16.0 mg/kg; s.c.) and memantine (0.15-20.0 mg/kg; s.c.), following daily administration for 3 days were tested in the social interaction test to determine their ability to reproduce the negative and positive symptoms measured by social isolation and stereotyped behavior, respectively. Second, the compounds were tested in the motility test following acute administration to determine their ability to induce locomotor hyperactivity reflecting the positive symptoms. In line with previous findings, all examined NMDA receptor antagonists produced social interaction deficits, locomotor hyperactivity, and stereotypy except memantine. Notably, this study found that MTEP following both acute and subchronic administration dose-dependently induced social isolation, but did not cause either locomotor hyperactivity or stereotypy. These data demonstrate that social behavior deficits in rats can be caused by both the blockade of the NMDA receptor and the inhibition of mGluR5, whereas mGluR5 antagonists may not independently be able to mimic the positive symptoms.

A preliminary study of the levels of testis oxidative stress parameters after MK-801-induced experimental psychosis model: protective effects of CAPE

We evaluated the effects of caffeic acid phenethyl ester (CAPE) on antioxidant enzyme levels and histopathologic changes in dizocilpine (MK-801) induced schizophrenic rat testis. A total of 30 adult male Wistar-Albino rats were divided into three groups. Group-I was used as control. Rats in the Group-II were intraperitoneally injected with MK-801, whereas those in Group-III were intraperitoneally injected with CAPE in addition to MK-801. The testes were collected for biochemical and histopathological examinations. Antioxidant enzyme activities, malondialdehyde, protein carbonyl and nitric oxide levels in testicular tissues were analyzed with spectrophotometric methods. Induction of schizophrenia resulted in a significant oxidative stress by increasing the levels of antioxidant enzymes. Tissue malondialdehyde and protein carbonyl levels were also increased. Treatment with CAPE led to significant decrease in oxidative injury. Administration of CAPE reduced the detrimental histopathologic changes caused by MK-801. The results showed that experimentally induced schizophrenia caused oxidative stress in testes of rats and treatment with CAPE reduced these harmful effects.