Ketamine-induced changes in rat behaviour: A possible animal model of 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.

Pharmacological characterization of psychosis-like behavior in the MPTP-lesioned nonhuman primate model of Parkinson's disease

Investigation of the pathophysiology of psychosis in Parkinson's disease (PD), as well as the assessment of potential novel therapeutics, has been limited by the lack of a well-validated animal model. MPTP-lesioned primates exhibit abnormal behaviors that are distinct from dyskinesia and parkinsonism and may represent behavioral correlates of neural processes related to psychosis in PD. Here we assess four types of behavior--agitation, hallucinatory-like responses to nonapparent stimuli, obsessive grooming, and stereotypies that are termed "psychosis-like"--and define their pharmacology using a psychosis-like behavior rating scale. By assessing the actions of drugs known to enhance or attenuate psychosis in PD patients, we find that the pharmacology of these behaviors recapitulates, in several respects, the pharmacology of psychosis in PD. Thus, levodopa and apomorphine elicited psychosis-like behaviors. Amantadine significantly decreased levodopa-induced dyskinesia but exacerbated psychosis-like behaviors. Haloperidol reduced psychosis-like behaviors but at the expense of increased parkinsonian disability while the atypical neuroleptics clozapine and quetiapine reduced psychosis-like behaviors without significant effect on parkinsonian disability. The response of different components of the psychotomimetic behavior suggested the involvement of both dopaminergic and nondopaminergic mechanisms in their expression.

Neural stem cell therapy for neuropsychiatric disorders

OBJECTIVE

To conduct a comprehensive literature review of the area of neural stem cells and neuropsychiatry.

METHODS

'Neural stem cells' (NSCs) and 'neurogenesis' were used as keywords in Medline (1966 - November 2006) to identify relevant papers in the areas of Alzheimer's disease (AD), depression, schizophrenia and Parkinson's disease (PD). This list was supplemented with papers from reference lists of seminal reviews.

RESULTS

The concept of a 'stem cell' continues to evolve and is currently defined by operational criteria related to symmetrical renewal, multipotency and functional viability. In vivo adult mammalian neurogenesis occurs in discrete niches in the subventricular and subgranular zones - however, functional precursor cells can be generated in vitro from a wide variety of biological sources. Both artificial and physiological microenvironment is therefore critical to the characteristics and behaviour of neural precursors, and it is not straightforward how results from the laboratory can be extrapolated to the living organism. Transplant strategies in PD have shown that it is possible for primitive neural tissue to engraft into neuropathic brain areas, become biologically functional and lead to amelioration of clinical signs and symptoms. However, with long-term follow-up, significant problems related to intractable side-effects and potential neoplastic growth have been reported. These are therefore the potentials and pitfalls for NSC technology in neuropsychiatry. In AD, the physiology of amyloid precursor protein may directly interact with NSCs, and a role in memory function has been speculated. The role of endogenous neurogenesis has also been implicated in the etiology of depression. The significance of NSCs and neurogenesis for schizophrenia is still emerging.

CONCLUSIONS

There are a number of technical and conceptual challenges ahead before the promise of NSCs can be harnessed for the understanding and treatment of neuropsychiatric disorders. Further research into fundamental NSC biology and how this interacts with the neuropsychiatric disease processes is required.

Long-term effects of developmental PCP administration on sensorimotor gating in male and female rats

RATIONALE

Acutely administered N-methyl-D-asparate (NMDA) antagonists are used to model schizophrenia, as measured by impairments in sensorimotor gating reflected in decreases in prepulse inhibition of the startle response (PPI). Aspects of acute NMDA receptor antagonism limit the applications of these models.

OBJECTIVE

The aim of this paper is to determine the long-term effects of developmental phencyclidine (PCP) treatment on sensorimotor gating in both male and female rats.

MATERIALS AND METHODS

Male and female Sprague Dawley rats were injected with PCP (10 mg/kg s.c.) on postnatal days (PN) 7, 9, and 11 and were tested for PPI on PN 32-34. The groups were then divided and some of the animals received a single dose of PCP (10 mg/kg s.c.) on PN 45. The animals were tested again for PPI at approximately 1, 4, and 6 weeks after the treatment.

RESULTS

There were no significant effects of neonatal-only treatment. One week after the PN 45 treatment, animals that were treated as neonates and as adolescents (PCP/PCP) were significantly impaired in PPI in both sexes. Male and female PCP/PCP rats also had significant increases in acoustic startle response 4 weeks posttreatment, which subsequently declined. PPI impairments in both sexes recovered over time and the adolescent-only treated females showed significant increases (improvement) in PPI approximately 6 weeks posttreatment.

CONCLUSION

These data suggest that treatment with an NMDA receptor antagonist during adolescence or early adulthood can produce a relatively long-term impairment of PPI (approximately 1 week) and that this effect is more pronounced in male animals.

Ketamine dose-dependently induces high-frequency oscillations in the nucleus accumbens in freely moving rats

BACKGROUND

In humans, subanesthetic doses of ketamine and recovery from ketamine anesthesia are associated with psychotic-like behavior. In rodents, ketamine produces hyperactivity, stereotypies, and abnormal social interaction used to model certain features of schizophrenia. Increasing evidence has implicated aberrant activity in the nucleus accumbens (NAc) with the pathophysiology of schizophrenia.

METHODS

Here, we examined the effect of an IP injection of ketamine (10, 25, 50, and 200 mg/kg) and d-amphetamine (3 mg/kg) on local field potentials in the rodent NAc. Locomotor activity was recorded simultaneously.

RESULTS

Spontaneous high-frequency oscillations (HFO) (140-180 Hz) were present in local field potentials recorded from the NAc. Ketamine dose-dependently induced rapid and substantial increases in HFO that correlated with behavioral hyperactivity. Similarly, large increases in HFO occurred during recovery from ketamine anesthesia. In contrast, d-amphetamine, which induced locomotor activity, produced only small increases in HFO.

CONCLUSIONS

We propose that ketamine-induced abnormal increases in HFO form part of the complex neurological changes in this model of schizophrenia. Ketamine-induced increases in HFO, although sharing similar temporal dynamics to hyperactivity, may not be functionally related to increased movement.

Pain sensitivity is altered in animals after subchronic ketamine treatment

RATIONALE

Clinical observations have shown that pain sensitivity is altered in some schizophrenic patients.

OBJECTIVES

To study alterations in pain sensitivity, the ketamine model in schizophrenia research was employed.

MATERIALS AND METHODS

Rats were subchronically injected with the dissociative anaesthetic ketamine (Ket, ten injections of 30 mg/kg, one injection per day over a period of 10 days). Two weeks after treatment completion, the animals' pain sensitivity was assayed in the hot plate test and they were subjected to electrical stimulation of the tail root. In addition, the effect of morphine was studied.

RESULTS

In group-housed animals, there was no difference between Ket-injected animals and control rats as measured in both nociceptive tests. In singly housed Ket-injected rats, pain threshold was increased in the electrical stimulation test. This suggests that stress due to single housing might be essential for modifications of pain sensitivity. Moreover, the antinociceptive effect of morphine was modified after single housing. Interestingly, the effect of morphine on locomotor activity was similar in both groups. In group-housed rats, mu receptor binding was unchanged in the frontal cortex, whereas Ket-injected animals had decreased levels in the hippocampus. In singly housed animals, mu receptor binding in Ket-injected rats increased in the frontal cortex and decreased in the hippocampus. (35)S-GTPgamma-S binding increased in the frontal cortex in both singly housed groups, but remained unchanged in the hippocampus.

CONCLUSIONS

The data suggest that the ketamine model might be useful for studying altered pain sensitivity in schizophrenia. Moreover, the data suggest that modifications in mu opioid receptor binding contribute to this phenomenon.

Determination of kynurenine levels in rat plasma by high-performance liquid chromatography with pre-column fluorescence derivatization

Kynurenine (KYN), a tryptophan metabolite, is a crucial compound for modulating neurotransmission because it can be metabolized in vivo into both quinolinic acid and kynurenic acid, which are the agonist and antagonist, respectively, of N-methyl-d-aspartate receptor. For the highly sensitive detection of KYN by high-performance liquid chromatography (HPLC), a fluorescence derivatization of KYN with a benzofurazan-type fluorogenic reagent, 4-N,N-dimethylaminosulfonyl-7-fluoro-2,1,3-benzoxadiazole (DBD-F) was investigated in the present study. KYN was derivatized with DBD-F (DBD-KYN) at 60 degrees C for 30 min, and separated on an octadecylsilica column with a gradient elution of the mobile phase, which consists of 0.1% formic acid in acetonitrile/methanol/water. DBD-KYN was detected fluorimetrically at 553 nm with an excitation wavelength of 431 nm. The limits of detection and quantification were approximately 0.30 pmol [signal-to-noise ratio (S/N) 3] and 1.0 pmol (S/N, 10) on column, respectively. Plasma KYN levels were successfully determined using 10 microL of rat plasma with satisfactory precision and accuracy. Intra- and inter-day precisions and accuracies were 1.7-6.8%, and -10 to 9.6%, respectively. KYN levels in plasma of male Sprague-Dawley rats (7 weeks old) were approximately 2.4+/-0.32 micromol L(-1) (n=4). The proposed HPLC method was applied to determine KYN levels in the plasma of ketamine-treated rats--the animal model of schizophrenia.

Developmental vitamin D deficiency alters MK 801-induced hyperlocomotion in the adult rat: An animal model of schizophrenia

BACKGROUND

Developmental vitamin D (DVD) deficiency has been proposed as a risk factor for schizophrenia. The behavioral phenotype of adult rats subjected to transient low prenatal vitamin D is characterized by spontaneous hyperlocomotion but normal prepulse inhibition of acoustic startle (PPI). The aim of this study was to examine the impact of selected psychotropic agents and one well-known antipsychotic agent on the behavioral phenotype of DVD deplete rats.

METHODS

Control versus DVD deplete adult rats were assessed on holeboard, open field and PPI. In the open field, animals were given MK-801 and/or haloperidol. For PPI, the animals were given apomorphine or MK-801.

RESULTS

DVD deplete rats had increased baseline locomotion on the holeboard task and increased locomotion in response to MK-801 compared to control rats. At low doses, haloperidol antagonized the MK-801 hyperactivity of DVD deplete rats preferentially and, at a high dose, resulted in a more pronounced reduction in spontaneous locomotion in DVD deplete rats. DVD depletion did not affect either baseline or drug-mediated PPI response.

CONCLUSIONS

These results suggest that DVD deficiency is associated with a persistent alteration in neuronal systems associated with motor function but not those associated with sensory motor gating. In light of the putative association between low prenatal vitamin D and schizophrenia, the discrete behavioral differences associated with the DVD model may help elucidate the neurobiological correlates of schizophrenia.

Alterations of plasma and cerebrospinal fluid glutamate levels in rats treated with the N-methyl-D-aspartate receptor antagonist, ketamine

It has been reported that the repeated administration of a sub-anesthetic dose of an N-methyl-D-aspartate receptor antagonist, ketamine, can produce an animal model of schizophrenia. Since no information is available on the alterations of the amino acid levels in ketamine-treated rats, we investigated the amino acid composition in the plasma and cerebrospinal fluid of rats that were repeatedly administered with ketamine for 5 consecutive days (30 mg/kg/day). The plasma and cerebrospinal fluid amino acid compositions in the fifth week after cessation of repeated ketamine administration were determined by highperformance liquid chromatography with fluorescence detection using a pre-column fluorescence reagent, i.e. 4-fluoro-7nitro-2,1,3-benzoxadiazole. Among the amino acids investigated in the present study, the level of plasma glutamic acid increased significantly (p < 0.05), while that of the cerebrospinal fluid glutamic acid decreased significantly in the ketamine-treated rats as compared with these levels in control rats injected with saline (p < 0.05, n = 7). These alterations in the glutamic acid level in the plasma and cerebrospinal fluid resemble those in schizophrenic patients, suggesting that ketamine-treated rats may be a useful model for performing research on the pathophysiology of schizophrenia.

Effects of repeated phencyclidine administration on adult hippocampal neurogenesis in the rat

Dysfunctional maturation of neural networks, particularly hippocampus-prefrontal networks, may be of particular interest in determining the pathophysiology of schizophrenia. Phencyclidine (PCP)-induced symptoms in humans appear to offer a more complete model of schizophrenia than do amphetamine-induced symptoms. This study investigated the effects of intermittent i.p. injections of PCP (7.5 mg/kg) on cell proliferation and survival of granule cells in the dentate gyrus of the rat brain using quantitative immunohistochemical techniques for 5-bromo-2'-deoxyuridine (BrdU)-positive cells. After repeated PCP injection for 14 days, mean scores for stereotyped behavior increased with the number of injections, while scores for ataxia and backpedaling as serotonergic behaviors gradually decreased. The number of BrdU-positive cells decreased by 23% in the subgranular zone of the dentate gyrus by 24 h after repeated injections. However, decreased levels of BrdU-positive cells returned to control levels within 1 week. Differentiation of newly formed cells was not influenced. Repeated PCP administration after BrdU injection did not exert any effects on survival of newly generated cells. These findings suggest that transient disturbances of cell proliferation in the dentate gyrus occur under PCP-related behavioral abnormalities. Whether disturbed cell proliferation would thus be closely implicated in the development of behavioral sensitization induced by PCP administration is unclear, but this would possibly result from adaptation to new pharmacological conditions under behavioral sensitization or stressful conditions of PCP-related abnormal behaviors. Further studies are required to elucidate the biological significance of hippocampal neurogenesis in the mechanisms underlying the development of cognitive dysfunctions and the psychosis of schizophrenia.

Ketamine enhances the expression of serine racemase and D-amino acid oxidase mRNAs in rat brain

We have evaluated the effects of the acute administration of noncompetitive N-methyl-D-aspartate receptor antagonist, ketamine, on the expression of serine racemase and D-amino acid oxidase mRNAs in several brain areas of rats. The ketamine administration produced a dose-dependent and transient elevation in the levels of serine racemase and D-amino acid oxidase mRNAs in all the brain areas. These findings suggest that there is a relationship between the gene expression of the d-serine-related enzymes and the blockade of the N-methyl-D-aspartate receptors.

Transcriptional response to the neuroleptic-like compound Ampullosporin A in the rat ketamine model

Psychotic disorders affecting up to 1% of the human population represent pathological changes to the metabolic homeostasis of the brain. Increasing evidence in the literature suggests complex biochemical and/or transcriptional alterations accompanying schizophrenia-like phenomena. Sub-chronic treatment with sub-anaesthetic doses of ketamine induces schizophrenia-related psychotic alterations that can be used as an animal model in the study of this disorder. Ampullosporin A belongs to a specific group of pore-forming fungal peptides, peptaibols. We focused on the analysis of molecular events occurring in the brain of ketamine-pre-treated rats after administration of Ampullosporin A with neuroleptic-like activity. The complex experimental approach allowed us to correlate the use of low molecular weight substances with a transcriptome fingerprint in the prefrontal cortex. We found 63 genes to be up-regulated and 22 genes suppressed, with transthyretin, syndecan-1 and NeuroD1 showing the highest degree of up-regulation. Our results suggest the possibility that Ampullosporin A belongs to the group of neuroleptic-like compounds, inducing massive changes in neurotransmitter receptor composition, calcium signalling cascades and second messenger systems, and leading to the plastic reorganization of brain tissue, metabolic pathways and synapses.

Translational research in central nervous system drug discovery

Of all the therapeutic areas, diseases of the CNS provide the biggest challenges to translational research in this era of increased productivity and novel targets. Risk reduction by translational research incorporates the "learn" phase of the "learn and confirm" paradigm proposed over a decade ago. Like traditional drug discovery in vitro and in laboratory animals, it precedes the traditional phase 1-3 studies of drug development. The focus is on ameliorating the current failure rate in phase 2 and the delays resulting from suboptimal choices in four key areas: initial test subjects, dosing, sensitive and early detection of therapeutic effect, and recognition of differences between animal models and human disease. Implementation of new technologies is the key to success in this emerging endeavor.

Behavioral effects of ketamine and toxic interactions with psychostimulants

Background

The anesthetic drug ketamine (KT) has been reported to be an abused drug and fatal cases have been observed in polydrug users. In the present study, considering the possibility of KT-enhanced toxic effects of other drugs, and KT-induced promotion of an overdose without making the subject aware of the danger due to the attenuation of several painful subjective symptoms, the intraperitoneal (i.p.) KT-induced alterations in behaviors and toxic interactions with popular co-abused drugs, the psychostimulants cocaine (COC) and methamphetamine (MA), were examined in ICR mice.

Results

A single dose of KT caused hyperlocomotion in a low (30 mg/kg, i.p.) dose group, and hypolocomotion followed by hyperlocomotion in a high (100 mg/kg, i.p.) dose group. However, no behavioral alterations derived from enhanced stress-related depression or anxiety were observed in the forced swimming or the elevated plus-maze test. A single non-fatal dose of COC (30 mg/kg, i.p.) or MA (4 mg/kg, i.p.) caused hyperlocomotion, stress-related depression in swimming behaviors in the forced swimming test, and anxiety-related behavioral changes (preference for closed arms) in the elevated plus-maze test. For the COC (30 mg/kg) or MA (4 mg/kg) groups of mice simultaneously co-treated with KT, the psychostimulant-induced hyperlocomotion was suppressed by the high dose KT, and the psychostimulant-induced behavioral alterations in the above tests were reversed by both low and high doses of KT. For the toxic dose COC (70 mg/kg, i.p.)- or MA (15 mg/kg, i.p.)-only group, mortality and severe seizures were observed in some animals. In the toxic dose psychostimulant-KT groups, KT attenuated the severity of seizures dose-dependently. Nevertheless, the mortality rate was significantly increased by co-treatment with the high dose KT.

Conclusion

Our results demonstrated that, in spite of the absence of stress-related depressive and anxiety-related behavioral alterations following a single dose of KT treatment, and in spite of the KT-induced anticonvulsant effects and attenuation of stress- and anxiety-related behaviors caused by COC or MA, the lethal effects of these psychostimulants were increased by KT.

The many faces of nitric oxide in schizophrenia. A review

Intense research has been conducted in an effort to identify specific biological markers of schizophrenia. The gas nitric oxide (NO) is one of the most important signaling molecules involved in a plethora of cellular events that take place in the cardiovascular, immune and nervous systems of animals. This survey aims to demonstrate that NO and its metabolites play important roles in schizophrenia and have a significant influence on our understanding of the development, progression and treatment of the disease. Special emphasis is given to the impact of NO metabolism on processes known to be disturbed in schizophrenia (i.e., cell migration, formation of synapses, NMDA receptor mediated neurotransmission, membrane pathology and cognitive abilities). However, when comparing data on the NO metabolism in the brain tissue and body fluids of schizophrenics with those obtained from patients with other neurological and psychiatric diseases, it becomes clear that alterations of NO metabolism are not unique to, or indicative of, schizophrenia. Thus, NO and its metabolites are not suitable diagnostic tools to distinguish schizophrenia from psychically healthy control cases or from other brain disorders.

Ketamine induces dopamine-dependent depression of evoked hippocampal activity in the nucleus accumbens in freely moving rats

Noncompetitive NMDA receptor antagonists, such as ketamine, induce a transient schizophrenia-like state in healthy individuals and exacerbate psychosis in schizophrenic patients. In rodents, noncompetitive NMDA receptor antagonists induce a behavioral syndrome that represents an experimentally valid model of schizophrenia. Current experimental evidence has implicated the nucleus accumbens in the pathophysiology of schizophrenia and the psychomimetic actions of ketamine. In this study, we have demonstrated that acute systemic administration of ketamine, at a dose known to produce hyperlocomotion and stereotypy, depressed the amplitude of the monosynaptic component of fimbria-evoked field potentials recorded in the nucleus accumbens. A similar effect was observed using the more selective antagonist dizocilpine maleate, indicating the depression was NMDA receptor dependent. Paired-pulse facilitation was enhanced concomitantly with, and in proportion to, ketamine-induced depressed synaptic efficacy, indicative of a presynaptic mechanism of action. Notably, the depression of field potentials recorded in the nucleus accumbens was markedly reduced after a focal 6-hydroxydopamine lesioning procedure in the nucleus accumbens. More specifically, pretreatment with the D2/D4 antagonist haloperidol, but not the D1 antagonist SCH23390 blocked ketamine-induced depression of nucleus accumbens responses. Our findings provide supporting evidence for the contemporary theory of schizophrenia as aberrant excitatory neurotransmission at the level of the nucleus accumbens.

Transient prenatal vitamin D deficiency is associated with subtle alterations in learning and memory functions in adult rats

Based on clues from epidemiology, low prenatal vitamin D has been proposed as a candidate risk factor for schizophrenia. Recent animal experiments have demonstrated that transient prenatal vitamin D deficiency is associated with persistent alterations in brain morphology and neurotrophin expression. In order to explore the utility of the vitamin D animal model of schizophrenia, we examined different types of learning and memory in adult rats exposed to transient prenatal vitamin D deficiency. Compared to control animals, the prenatally deplete animals had a significant impairment of latent inhibition, a feature often associated with schizophrenia. In addition, the deplete group was (a) significantly impaired on hole board habituation and (b) significantly better at maintaining previously learnt rules of brightness discrimination in a Y-chamber. In contrast, the prenatally deplete animals showed no impairment on the spatial learning task in the radial maze, nor on two-way active avoidance learning in the shuttle-box. The results indicate that transient prenatal vitamin D depletion in the rat is associated with subtle and discrete alterations in learning and memory. The behavioural phenotype associated with this animal model may provide insights into the neurobiological correlates of the cognitive impairments of schizophrenia.

Rolipram attenuates MK-801-induced deficits in latent inhibition

Latent inhibition is used to examine attention and study cognitive deficits associated with schizophrenia. Research using MK-801, an N-methyl-D-aspartate (NMDA) open channel blocker, implicates glutamate receptors in acquisition of latent inhibition of cued fear conditioning. Evidence suggests an important relationship between NMDA-induced increases in cyclic adenosine monophosphate (cAMP) and learning and memory. The authors examine whether amplification of the cAMP signaling pathway by rolipram, a selective Type 4 cAMP phosphodiesterase inhibitor, reverses MK-801-induced impairments in latent inhibition. One day before training, mice were injected with MK-801, rolipram, MK-801 and rolipram, or vehicle and received 20 preexposures or no preexposures to an auditory conditioned stimulus (CS). Training consisted of 2 CS-footshock unconditioned stimulus pairings. Rolipram attenuated the disruptive effect of MK-801 on latent inhibition, which suggests a role for the cAMP signaling pathway in the task and implicates phosphodiesterase inhibition as a target for treating cognitive impairments associated with schizophrenia.

Ketamine-induced distractibility: An oculomotor study in monkeys

BACKGROUND

Administration of subanesthetic doses of ketamine, a noncompetitive N-methyl-D-aspartate receptor antagonist, induces a spectrum of behavioral disorders that are commonly observed in patients with schizophrenia. Although it has been demonstrated that poor antisaccade performance is a core dysfunction in schizophrenia, the ability of ketamine to induce an increased distractibility has not been demonstrated. The present study aimed to determine whether ketamine administration would reproduce the same antisaccade deficit as that observed in schizophrenic subjects.

METHODS

We studied the effect of acute ketamine or saline administration on the performance of two monkeys trained on a reflexive visually guided saccade task and an antisaccade task.

RESULTS

The main result is that ketamine administration induced a markedly increased antisaccade error rate and increased antisaccade latency, similar to that seen in schizophrenic subjects. Other impairments consisted of increased reflexive saccade latency and the presence of a gaze-evoked nystagmus.

CONCLUSIONS

This study supports the validity of ketamine as a pharmacological model of schizophrenia. Based on the known pharmacological effects of ketamine, further studies should allow the investigation of the pharmacological basis of distractibility.

Ketamine-induced changes in rat behaviour: a possible animal model of schizophrenia. Test of predictive validity

Previously, it was shown that subchronic application of the NMDA receptor antagonist ketamine (Ket) induces schizophrenia-related alterations, e.g. decreased non-aggressive behaviour in the social interaction test, which might be a useful animal model in the study of negative symptoms of this disease. In order to further evaluate the predictive validity of this model, the anxioloytic diazepam, the classic neuroleptic haloperidol and the atypical neuroleptics clozapine and risperidone were tested after acute and subchronic treatment. The experiments demonstrated that haloperidol did not normalise the behavioural effects of Ket. After acute administration, diazepam was ineffective in control animals but increased non-aggressive behaviour in Ket-treated animals. Similar effects were found in animals injected with either clozapine or risperidone. Twenty-four hours after discontinuation of subchronic treatment with both substances, there was an increase in the percentage of non-aggressive behaviour in the ketamine group and a decrease in the control animals. This decrease was explained in terms of withdrawal. Different effects in the control groups and the Ket groups were found when the test was performed 1 h after subchronic clozapine or risperidone treatment. The data suggest that atypical antipsychotic drugs (APD) effectively counteract Ket-induced alterations in social behaviour. Regarding false-positive effects by anxiolytic drugs without antipsychotic efficacy, this model may have some predictive validity for identifying anxiolytic effects of novel antipsychotic compounds.

Effects on rat thalamic proteome by acute and subchronic MK-801-treatment

Since the symptoms of intoxication with non-competitive N-methyl-D-aspartate (NMDA) receptor antagonists closely mimic symptoms in patients with schizophrenia, [+]-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]-cycloheptene-5,10-iminehydrogenmaleate (MK-801)-treated rodents are often used as a model for schizophrenia. In most studies, acute injections of MK-801 to rats have been used, but in some studies, longer periods of treatment have been performed. In our previous work, alterations in mRNA/protein expression were screened in the cerebral cortex of MK-801 treated rats. Different proteins were altered in different treatment courses of MK-801. The main objective of the present study was to evaluate different treatment periods of treatment with MK-801 in rats as a model for schizophrenia. Thalamus proteins from treated (acute, six and 12 days) and control rats were analyzed with two-dimensional gel electrophoresis and mass spectrometry. Our results show that different treatment times of MK-801 to rats give different biochemical results. Therefore, it is important to use the same treatment time in studies that will be compared.

Rat-PET study without anesthesia: Anesthetics modify the dopamine D1 receptor binding in rat brain

Positron emission tomography (PET) measurements in 6-month-old F344/N rats were performed in the conscious state and the influence of chloral hydrate, ketamine, and pentobarbital anesthesia on dopamine D(1) (DA-D(1)) receptor binding was evaluated using [(11)C]SCH23390, a selective DA-D(1) receptor ligand. To perform the PET study in conscious rats, an original fixation apparatus was developed and the animals were trained to acclimate to the scanning atmosphere for 3 h. This training was carried out twice a day for 2 weeks. PET measurements in conscious rats were successful, since the trained rats scarcely moved during the scanning (as monitored by video camera) and since highly reproducible measurements of binding potential (BP) were derived from their scanning. Chloral hydrate and ketamine anesthesia significantly increased the striatal BP of DA-D(1) receptors by 36% and 46%, respectively, compared to that observed in the conscious state. In contrast, pentobarbital markedly decreased the BP by 41%. These BP values of DA-D(1) receptors were calculated using a curve-fitting method. Our results indicate that PET studies in rats should be performed in the conscious state since the anesthetics dramatically modified ligand-receptor bindings, such as DA-D(1) receptor binding, in rat brain.

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.

Increased neurogenesis in a rat ketamine model of schizophrenia

BACKGROUND

Growing evidence implicates abnormal neurodevelopment in schizophrenia, which manifests itself, for example, in reduced volume and cellular disarray of the hippocampus. This prompted us to investigate if there are indications of an altered neurodevelopment in this brain region. While neuron birth is largely completed by the end of gestation, granule neurons of the dentate gyrus are generated throughout life, thus offering an opportunity to investigate neurogenesis postnatally.

METHODS

We investigated whether repeated application of subanesthetic doses of the noncompetitive N-methyl-D-aspartate receptor antagonist ketamine, which has been shown to mimic model aspects of schizophrenia in animals, affects the hippocampal neurogenesis detected by bromodeoxyuridine incorporation. Cells were identified by immunocytochemistry.

RESULTS

Subanesthetic doses of ketamine applied subchronically enhance neurogenesis in the hippocampal subgranular zone.

CONCLUSIONS

In our animal model of schizophrenia, ketamine may evoke its stimulating effect on neurogenesis via a block of the N-methyl-D-aspartate receptor directly by reducing the c-Fos/c-Jun expression, resulting in a depression of the AP1 transcription factor complex and/or by a reduced nitric oxide production or an enhanced serotonergic activity. The newly formed neurons are not able to overcome the schizophrenia-related loss of parvalbumin expressing neurons and the behavioral abnormalities indicating that their functional integration is crucial.

Combined prenatal and chronic postnatal vitamin D deficiency in rats impairs prepulse inhibition of acoustic startle

There is growing evidence that 1,25-dihydroxyvitamin D3 is involved in normal brain development. The aim of this study was to examine the impact of prenatal and postnatal hypovitaminosis D on prepulse inhibition (PPI) of acoustic startle in adult rats. We compared six groups of rats: control rats with normal vitamin D throughout life and normal litter size (Litter); control rats with normal vitamin D but with a reduced litter size of two (Control); offspring from reduced litters of vitamin D deplete mothers who were repleted at birth (Birth), repleted at weaning (Weaning) or remained on a deplete diet until 10 weeks of age (Life); or control rats that were placed on a vitamin D-deficient diet from 5 to 10 weeks of age (Adult). All rats were tested in acoustic startle chambers at 5 and 10 weeks of age for acoustic startle responses and for PPI. There were no significant group differences at 5 weeks of age on the acoustic startle response or on PPI. At 10 weeks of age, rats in the Life group only had impaired PPI despite having normal acoustic startle responses. We conclude that combined prenatal and chronic postnatal hypovitaminosis D, but not early life hypovitaminosis D, alters PPI.