A conceptual and practical guide to the behavioural evaluation of animal models of the symptomatology and therapy of schizophrenia

The adenosine hypothesis of schizophrenia into its third decade: From neurochemical imbalance to early life etiological risks

The adenosine hypothesis of schizophrenia was conceptualized about two decades ago in an attempt to integrate two prominent theories of neurochemical imbalance that attribute the pathogenesis of schizophrenia to hyperfunction of the mesocorticolimbic dopamine neurotransmission and hypofunction of cortical glutamate neurotransmission. Given its unique position as an endogenous modulator of both dopamine and glutamate signaling in the brain, adenosine was postulated as a potential new drug target to achieve multiple antipsychotic actions. This new strategy may offer hope for improving treatment, especially in alleviating negative symptoms and cognitive deficits of schizophrenia that do not respond to current medications. To date, however, the adenosine hypothesis has yet led to any significant therapeutic breakthroughs. Here, we address two possible reasons for the impasse. First, neither the presence of adenosine functional deficiency in people with schizophrenia nor its causal relationship to symptom production has been satisfactorily examined. Second, the lack of novel adenosine-based drugs also impedes progress. This review updates the latest preclinical and clinical data pertinent to the construct validity of the adenosine hypothesis and explores novel molecular processes whereby dysregulation of adenosine signaling could be linked to the etiology of schizophrenia. It is intended to stimulate and revitalize research into the adenosine hypothesis towards the development of a new and improved generation of antipsychotic drugs that has eluded us for decades.

Prenatal methotrexate injection increases behaviors possibly associated with depression and/or autism in rat offspring; A new animal model for mental disorder, based on folate metabolism deficit during pregnancy

Background

Deficiency of folate, an essential vitamin for DNA synthesis and methylation, is reported as a risk factor for mental disorders. Considering a possibility that folate metabolism deficit during pregnancy may disturb CNS development and increase mental disorders in offspring, we treated pregnant rats with methotrexate (MTX), an inhibitor of folate metabolic enzyme, and evaluated offspring behaviors.

Methods

Saline or MTX was intraperitoneally administered to female SD rats on gestational day 17. Offspring behaviors were evaluated during approximately 6–9 weeks old; prepulse inhibition (PPI), social interaction (SI), locomotor activity (LA), and forced swimming test (FST) for evaluation of schizophrenia, depression, and autism related behaviors; the elevated plus maze (EPM) and the light–dark box (LD) test for evaluation of anxiety.

Results

Compared to saline‐treated group, MTX‐treated group showed decrease of SI and increase of immobility time in FST. In addition, increases of time spent in the light box and shuttling between the light–dark boxes were observed in LD test. On the other hand, no changes were confirmed in EPM, LA, and PPI.

Conclusion

Decrease of SI and increase of immobility time in FST may suggest association of this animal model with depression and/or autism. Increase of time spent in the light box and shuttling between the light–dark boxes may indicate changes in anxiety or cognitive level to environment, or repetitive behaviors in autism. Although further studies are warranted to characterize this animal model, at least we can say that prenatal MTX exposure, possibly causing folate metabolism deficit, affects offspring behaviors.

Brain Derived Neurotrophic Factor Deficiency is Associated with Cognitive Impairment and Elevated Phospholipase A2 Activity in Plasma of Mice

Decreased levels of Brain-Derived Neurotrophic Factor (BDNF) are a common finding in schizophrenia. Another well-documented protein linked to schizophrenia is intracellular Ca²⁺-independent Phospholipase (PLA2). However, the potential association between PLA2 and BDNF with regard to schizophrenia has yet to be examined. In the present study, male and female BDNF knockout mice, a possible genetic model of schizophrenia, were exposed to prenatal stress and tested in the nest test, open field test and T-maze. Following behavioral tests, whole brain and plasma samples were harvested to measure the activity of PLA2. BDNF knockout mice showed cognitive deficits in the T-maze. Furthermore, there was a quadratic association of PLA2 with performance in the open field test. Moreover, BDNF deficiency and female sex were associated with elevated plasma PLA2 levels. The cognitive impairment of BDNF heterozygous mice as well as their increased PLA2 activity in plasma is consistent with findings in schizophrenia patients. The particular elevation of PLA2 activity in females may partly explain sex differences of clinical symptoms in schizophrenia (e.g. age of onset, severity of symptoms). Additionally, PLA2 was significantly correlated with body and adrenal weight after weaning, whereby the latter emphasizes the possible connection of PLA2 with steroidogenesis.

Innovative screening models for the discovery of new schizophrenia drug therapies: an integrated approach

Introduction: Schizophrenia is a severe psychiatric disorder affecting millions worldwide. However, available treatment options do not fully address the disease. Whereas current antipsychotics may control psychotic symptoms, they seem notoriously ineffective in improving negative and cognitive symptoms or in preventing functional decline. As the etiology of schizophrenia eludes us, the development of valid animal models for screening new drug targets appears to be a strenuous task.Areas covered: In this review, the authors present the key concepts that validate animal models of schizophrenia, as well as the different screening approaches for novel schizophrenia treatments. The models covered are either based on major neurotransmitter systems or neurodevelopmental, immune, and genetic approaches.Expert opinion: Sadly, due to inertia, research focuses on developing 'anti-psychotics', instead of 'anti-schizophrenia' drugs that would tackle the entire syndrome of schizophrenia. Whereas no perfect model may ever exist, combining different experimental designs may enhance validity, as the over-reliance on a single model is inappropriate. Multi-model approaches incorporating vulnerability, the 'two-hit' hypothesis, and endophenotypes offer a promise for developing new strategies for schizophrenia treatment. Forward and reverse translation between preclinical and clinical research will increase the probability of success and limit failures in drug development.

Behavioral Tasks Evaluating Schizophrenia-like Symptoms in Animal Models: A Recent Update

BACKGROUND

Schizophrenia is a serious mental illness that affects more than 21 million people worldwide. Both genetics and the environment play a role in its etiology and pathogenesis. Symptoms of schizophrenia are mainly categorized into positive, negative, and cognitive. One major approach to identify and understand these diverse symptoms in humans has been to study behavioral phenotypes in a range of animal models of schizophrenia.

OBJECTIVE

We aimed to provide a comprehensive review of the behavioral tasks commonly used for measuring schizophrenia-like behaviors in rodents together with an update of the recent study findings.

METHODS

Articles describing phenotypes of schizophrenia-like behaviors in various animal models were collected through a literature search in Google Scholar, PubMed, Web of Science, and Scopus, with a focus on advances over the last 10 years.

RESULTS

Numerous studies have used a range of animal models and behavioral paradigms of schizophrenia to develop antipsychotic drugs for improved therapeutics. In establishing animal models of schizophrenia, the candidate models were evaluated for schizophrenia-like behaviors using several behavioral tasks for positive, negative, and cognitive symptoms designed to verify human symptoms of schizophrenia. Such validated animal models were provided as rapid preclinical avenues for drug testing and mechanistic studies.

CONCLUSION

Based on the most recent advances in the field, it is apparent that a myriad of behavior tests are needed to confirm and evaluate the congruency of animal models with the numerous behaviors and clinical signs exhibited by patients with schizophrenia.

Translation-Focused Approaches to GPCR Drug Discovery for Cognitive Impairments Associated with Schizophrenia

There are no effective therapeutics for cognitive impairments associated with schizophrenia (CIAS), which includes deficits in executive functions (working memory and cognitive flexibility) and episodic memory. Compounds that have entered clinical trials are inadequate in terms of efficacy and/or tolerability, highlighting a clear translational bottleneck and a need for a cohesive preclinical drug development strategy. In this review we propose hippocampal-prefrontal-cortical (HPC-PFC) circuitry underlying CIAS-relevant cognitive processes across mammalian species as a target source to guide the translation-focused discovery and development of novel, procognitive agents. We highlight several G protein-coupled receptors (GPCRs) enriched within HPC-PFC circuitry as therapeutic targets of interest, including noncanonical approaches (biased agonism and allosteric modulation) to conventional clinical targets, such as dopamine and muscarinic acetylcholine receptors, along with prospective novel targets, including the orphan receptors GPR52 and GPR139. We also describe the translational limitations of popular preclinical cognition tests and suggest touchscreen-based assays that probe cognitive functions reliant on HPC-PFC circuitry and reflect tests used in the clinic, as tests of greater translational relevance. Combining pharmacological and behavioral testing strategies based in HPC-PFC circuit function creates a cohesive, translation-focused approach to preclinical drug development that may improve the translational bottleneck currently hindering the development of treatments for CIAS.

An Overview of Animal Models Related to Schizophrenia

Schizophrenia is a heterogeneous psychiatric disorder that is poorly treated with current therapies. In this brief review, we provide an update regarding the use of animal models to study schizophrenia in an attempt to understand its aetiology and develop novel therapeutic strategies. Tremendous progress has been made developing and validating rodent models that replicate the aetiologies, brain pathologies, and behavioural abnormalities associated with schizophrenia in humans. Here, models are grouped into 3 categories-developmental, drug induced, and genetic-to reflect the heterogeneous risk factors associated with schizophrenia. Each of these models is associated with varied but overlapping pathophysiology, endophenotypes, behavioural abnormalities, and cognitive impairments. Studying schizophrenia using multiple models will permit an understanding of the core features of the disease, thereby facilitating preclinical research aimed at the development and validation of better pharmacotherapies to alter the progression of schizophrenia or alleviate its debilitating symptoms.

Probable mechanisms involved in the antipsychotic-like activity of morin in mice

Evidence derived from preliminary studies suggests that morin, a neuroactive flavonoid with proven antioxidant and antiinflammatory properties possess antipsychotic-like activity. The present study was designed to evaluate the probable mechanisms involve in the antipsychotic-like activity of morin in ketamine model of schizophrenia. The effects of morin, haloperidol and risperidone on neurobehavioral and anti-schizophrenia-like effects were evaluated in mice (n = 7) following intraperitoneal (i.p.) administration of morin (25-100 mg/kg), haloperidol (1 mg/kg) and risperidone (0.5 mg/kg) alone or in combination with ketamine (20 mg/kg, i.p.) for 10 days. Neurobehavioral and schizophrenia-like activities consisting of open-field (positive symptoms), Y-maze, novel-object recognition (cognitive symptoms), social interaction (negative symptoms) tests were assessed. Also, wood-block catalepsy and rota-rod tests were employed to evaluate extrapyramidal side effects of morin. Thereafter, brain levels of biomarkers of oxidative, nitrergic and acetylcholinesterase alterations as well as histomorphological changes in the striatum and prefrontal-cortex were determined. Administration of morin and risperidone alone but not haloperidol significantly (p > 0.05) prevented ketamine-induced hyperlocomotion, social withdrawal and cognitive impairments relative to controls, and were devoid of extrapyramidal side effects. Morin alone or in combination with ketamine significantly increased glutathione concentration, superoxide dismutase and catalase activities compared with saline- or ketamine-treated mice. Moreover, morin alone or in combination with ketamine also significantly decreased malondialdehyde, nitrite and acetylcholinesterase alterations in mice brains. Furthermore, morin prevented ketamine-induced brain neuronal alterations in the striatum and prefrontal-cortex. Together, our findings suggest that morin may demonstrate antipsychotic-like therapeutic effect via modulation of oxidative/nitrergic, cholinergic actions and neuroprotection.

Enhancement of In Vivo Efficacy and Oral Bioavailability of Aripiprazole with Solid Lipid Nanoparticles

Aripiprazole (ARP), a second-generation or atypical antipsychotic, is poorly soluble and undergoes extensive hepatic metabolism and P-glycoprotein efflux which lead to reduced in vivo efficacy and increased dose-related side effects. To enhance in vivo efficacy and oral bioavailability of aripiprazole, aripiprazole-loaded solid lipid nanoparticles (SLNs) were developed using tristearin as solid lipid. Tween 80 and sodium taurocholate were used as surfactants to prepare SLNs using microemulsification method. SLNs were characterized for particle size, zeta potential, entrapment efficiency, and crystallinity of lipid and drug. In vitro release studies were performed in water containing 0.5% sodium dodecyl sulfate. Pharmacodynamic evaluation was carried out in laca mice using dizocilpine-induced schizophrenic model where behavioral evaluation revealed better in vivo efficacy of SLNs. Pharmacokinetics of aripiprazole-loaded SLNs after oral administration to conscious male Wistar rats was studied. Bioavailability of aripiprazole was increased 1.6-fold after formulation of aripiprazole into SLNs as compared to plain drug suspension. The results indicated that solid lipid nanoparticles can improve the bioavailability of lipophilic drugs like aripiprazole by enhancement of absorption and minimizing first-pass metabolism.

Aripiprazole, A Drug that Displays Partial Agonism and Functional Selectivity

BACKGROUND

The treatment of schizophrenia is challenging due to the wide range of symptoms (positive, negative, cognitive) associated with the disease. Typical antipsychotics that antagonize D2 receptors are effective in treating positive symptoms, but extrapyramidal side-effects (EPS) are a common occurrence. Atypical antipsychotics targeting 5-HT2A and D2 receptors are more effective at treating cognitive and negative symptoms compared to typical antipsychotics, but these drugs also result in side-effects such as metabolic syndromes.

OBJECTIVE

To identify evidence in the literature that elucidates the pharmacological profile of aripiprazole.s.

METHODS

We searched PubMed for peer reviewed articles on aripiprazole and its clinical efficacy, side-effects, pharmacology, and effects in animal models of schizophrenia symptoms.

RESULTS

Aripiprazole is a newer atypical antipsychotic that displays a unique pharmacological profile, including partial D2 agonism and functionally selective properties. Aripiprazole is effective at treating the positive symptoms of schizophrenia and has the potential to treat negative and cognitive symptoms at least as well as other atypical antipsychotics. The drug has a favorable side-effect profile and has a low propensity to result in EPS or metabolic syndromes. Animal models of schizophrenia have been used to determine the efficacy of aripiprazole in symptom management. In these instances, aripiprazole resulted in the reversal of deficits in extinction, pre-pulse inhibition, and social withdrawal. Because aripiprazole requires a greater than 90% occupancy rate at D2 receptors to be clinically active and does not produce EPS, this suggests a functionally selective effect on intracellular signaling pathways.

CONCLUSION

A combination of factors such as dopamine system stabilization via partial agonism, functional selectivity at D2 receptors, and serotonin-dopamine system interaction may contribute to the ability of aripiprazole to successfully manage schizophrenia symptoms. This review examines these mechanisms of action to further clarify the pharmacological actions of aripiprazole.

Estradiol and raloxifene modulate hippocampal gamma oscillations during a spatial memory task

Previous work suggests that estradiol regulates the expression of hippocampal parvalbumin as well as hippocampus-dependent spatial memory in mice. Parvalbumin interneurons generate neuronal oscillatory activity in the gamma frequency range (30-80Hz) and gamma oscillations are closely linked with higher cognitive functions. Raloxifene, a selective estrogen receptor modulator, shows beneficial effects on human cognitive performance, and has few peripheral side effects unlike estradiol, but the biological mechanisms which underpin these benefits are not clear. This study aimed to investigate whether estradiol and raloxifene modulate hippocampal gamma-band oscillations during spatial memory performance. Prepubescent female mice were ovariectomized (OVX) and implanted with a subcutaneous pellet of either estradiol (E2), raloxifene or placebo. During adulthood, local field potentials were recorded from the dorsal hippocampus while mice were performing the Y-maze hippocampus-dependent spatial memory task. Ovariectomy caused deficits in spatial memory, accompanied by a significant reduction in hippocampal gamma oscillations, specifically during decision making. Estradiol as well as raloxifene rescued both behavioural and electrophysiological deficits. These data have significant implications for disorders of cognitive impairment where altered gamma oscillations are apparent, such as schizophrenia.

Gestational exposure to perfluorooctanoic acid (PFOA): Alterations in motor related behaviors

Perfluoroalkyl and polyfluoroalkyl substances are used in commercial applications and developmental exposure has been implicated in alterations in neurobehavioral functioning. While associations between developmental perfluorooctanoic acid (PFOA) exposure and human outcomes have been inconsistent, studies in experimental animals suggest alterations in motor related behaviors. To examine a dose-response pattern of neurobehavioral effects following gestational exposure to PFOA, pregnant CD-1 mice received PFOA (0, 0.1, 0.3, 1.0mg/kg/day) via oral gavage from gestational day 1-17 and the male offspring examined. Motor activity assessments on postnatal day (PND)18, 19, and 20 indicated a shift in the developmental pattern with an elevated activity level observed in the 1.0mg/kg/day dose group on PND18. In the adult, no alterations were observed in body weights, activity levels, diurnal pattern of running wheel activity, startle response, or pre-pulse startle inhibition. In response to a subcutaneous injection of saline or nicotine (80μg/kg), all animals displayed a transient increase in activity likely associated with handling with no differences observed across dose groups. Inhibition of motor activity over 18days of 400μg/kg nicotine injection was not significantly different across dose groups. Hyperactivity induced by 2mg/kg (+)-methamphetamine hydrochloride intraperitoneal injection was significantly lower in the 1.0mg/kg/day PFOA dose group as compared to controls. Taken together, these data suggest that the effects on motor-related behaviors with gestational PFOA exposure do not mimic those reported for acute postnatal exposure. Changes were not observed at dose levels under 1.0mg/kg/day PFOA. Further examination of pathways associated with methamphetamine-induced activity is warranted.

Non-restraining EEG Radiotelemetry: Epidural and Deep Intracerebral Stereotaxic EEG Electrode Placement

Implantable EEG radiotelemetry is of central relevance in the neurological characterization of transgenic mouse models of neuropsychiatric and neurodegenerative diseases as well as epilepsies. This powerful technique does not only provide valuable insights into the underlying pathophysiological mechanisms, i.e., the etiopathogenesis of CNS related diseases, it also facilitates the development of new translational, i.e., therapeutic approaches. Whereas competing techniques that make use of recorder systems used in jackets or tethered systems suffer from their unphysiological restraining to semi-restraining character, radiotelemetric EEG recordings overcome these disadvantages. Technically, implantable EEG radiotelemetry allows for precise and highly sensitive measurement of epidural and deep, intracerebral EEGs under various physiological and pathophysiological conditions. First, we present a detailed protocol of a straight forward, successful, quick and efficient technique for epidural (surface) EEG recordings resulting in high-quality electrocorticograms. Second, we demonstrate how to implant deep, intracerebral EEG electrodes, e.g., in the hippocampus (electrohippocampogram). For both approaches, a computerized 3D stereotaxic electrode implantation system is used. The radiofrequency transmitter itself is implanted into a subcutaneous pouch in both mice and rats. Special attention also has to be paid to pre-, peri- and postoperative treatment of the experimental animals. Preoperative preparation of mice and rats, suitable anesthesia as well as postoperative treatment and pain management are described in detail.

EEG Radiotelemetry in Small Laboratory Rodents: A Powerful State-of-the Art Approach in Neuropsychiatric, Neurodegenerative, and Epilepsy Research

EEG radiotelemetry plays an important role in the neurological characterization of transgenic mouse models of neuropsychiatric and neurodegenerative diseases as well as epilepsies providing valuable insights into underlying pathophysiological mechanisms and thereby facilitating the development of new translational approaches. We elaborate on the major advantages of nonrestraining EEG radiotelemetry in contrast to restraining procedures such as tethered systems or jacket systems containing recorders. Whereas a main disadvantage of the latter is their unphysiological, restraining character, telemetric EEG recording overcomes these disadvantages. It allows precise and highly sensitive measurement under various physiological and pathophysiological conditions. Here we present a detailed description of a straightforward successful, quick, and efficient technique for intraperitoneal as well as subcutaneous pouch implantation of a standard radiofrequency transmitter in mice and rats. We further present computerized 3D-stereotaxic placement of both epidural and deep intracerebral electrodes. Preoperative preparation of mice and rats, suitable anaesthesia, and postoperative treatment and pain management are described in detail. A special focus is on fields of application, technical and experimental pitfalls, and technical connections of commercially available radiotelemetry systems with other electrophysiological setups.

Modeling combined schizophrenia-related behavioral and metabolic phenotypes in rodents

Schizophrenia is a chronic, debilitating disorder with a complex behavioral and cognitive phenotype underlined by a similarly complex etiology involving an interaction between susceptibility genes and environmental factors during early development. Limited progress has been made in developing novel pharmacotherapy, partly due to a lack of valid animal models. The recent recognition of the potentially causal role of central and peripheral energy metabolism in the pathophysiology of schizophrenia raises the need of research on animal models that combine both behavioral and metabolic phenotypic domains, similar to what have been identified in humans. In this review we focus on selected genetic (DBA/2J mice, leptin receptor mutants, and PSD-93 knockout mice), early neurodevelopmental (maternal protein deprivation) and pharmacological (acute phencyclidine) animal models that capture the combined behavioral and metabolic abnormalities shown by schizophrenic patients. In reviewing behavioral phenotypes relevant to schizophrenia we apply the principles established by the Research Domain Criteria (RDoC) for better translation. We demonstrate that etiologically diverse manipulations such as specific breeding, deletion of genes that are primarily involved in metabolic regulation and in synaptic plasticity, as well as early metabolic deprivation and adult pharmacological challenge of the glutamate system can lead to schizophrenia-related behavioral and metabolic phenotypes, which suggest that these pathways might be interlinked. We propose that using animal models that combine different domains of schizophrenia can be used as a translationally valid approach to capture the system-level complex interplay between peripheral and central processes in the development of psychopathology.

Coronin 1 regulates cognition and behavior through modulation of cAMP/protein kinase A signaling

The evolutionarily conserved protein coronin 1 is needed for activating the cyclic AMP signaling pathway in the brain and is important for cognition and behavior.

Cognitive and behavioral disorders are thought to be a result of neuronal dysfunction, but the underlying molecular defects remain largely unknown. An important signaling pathway involved in the regulation of neuronal function is the cyclic AMP/Protein kinase A pathway. We here show an essential role for coronin 1, which is encoded in a genomic region associated with neurobehavioral dysfunction, in the modulation of cyclic AMP/PKA signaling. We found that coronin 1 is specifically expressed in excitatory but not inhibitory neurons and that coronin 1 deficiency results in loss of excitatory synapses and severe neurobehavioral disabilities, including reduced anxiety, social deficits, increased aggression, and learning defects. Electrophysiological analysis of excitatory synaptic transmission in amygdala revealed that coronin 1 was essential for cyclic–AMP–protein kinase A–dependent presynaptic plasticity. We further show that upon cell surface stimulation, coronin 1 interacted with the G protein subtype Gαs to stimulate the cAMP/PKA pathway. The absence of coronin 1 or expression of coronin 1 mutants unable to interact with Gαs resulted in a marked reduction in cAMP signaling. Strikingly, synaptic plasticity and behavioral defects of coronin 1–deficient mice were restored by in vivo infusion of a membrane-permeable cAMP analogue. Together these results identify coronin 1 as being important for cognition and behavior through its activity in promoting cAMP/PKA-dependent synaptic plasticity and may open novel avenues for the dissection of signal transduction pathways involved in neurobehavioral processes.

Memory and behavior depend on the proper transduction of signals in the brain, but the underlying molecular mechanisms remain largely unknown. Coronin 1 is a member of a highly conserved family of proteins, and although its gene lies in a chromosome region associated with neurobehavioral dysfunction in mice and men, it has never been directly ascribed a specific function in the brain. Here we show that coronin 1 plays an important role in cognition and behavior by regulating the cyclic AMP (cAMP) signaling pathway. We find that when cell surface receptors are activated, coronin 1 stimulates cAMP production and activation of protein kinase A. Coronin 1 deficiency resulted in severe functional defects at excitatory synapses. Furthermore, in both mice and humans, deletion or mutation of coronin 1 causes severe neurobehavioral defects, including social deficits, increased aggression, and learning disabilities. Strikingly, treatment with a membrane-permeable analogue of cAMP restored synaptic plasticity and behavioral defects in mice lacking coronin 1. Together this work not only shows a critical role for coronin 1 in neurobehavior but also defines a role for the coronin family in regulating the transmission of signals within cells.

Prevention and reversal of ketamine-induced schizophrenia related behavior by minocycline in mice: Possible involvement of antioxidant and nitrergic pathways

It has been hypothesized that oxidative imbalance and alterations in nitrergic signaling play a role in the neurobiology of schizophrenia. Preliminary evidence suggests that adjunctive minocycline treatment is efficacious for cognitive and negative symptoms of schizophrenia. This study investigated the effects of minocycline in the prevention and reversal of ketamine-induced schizophrenia-like behaviors in mice. In the reversal protocol, animals received ketamine (20 mg/kg per day intraperitoneally or saline for 14 days, and minocycline (25 or 50 mg/kg daily), risperidone or vehicle treatment from days 8 to 14. In the prevention protocol, mice were pretreated with minocycline, risperidone or vehicle prior to ketamine. Behaviors related to positive (locomotor activity and prepulse inhibition of startle), negative (social interaction) and cognitive (Y maze) symptoms of schizophrenia were also assessed. Glutathione (GSH), thiobarbituric acid-reactive substances (TBARS) and nitrite levels were measured in the prefrontal cortex, hippocampus and striatum. Minocycline and risperidone prevented and reversed ketamine-induced alterations in behavioral paradigms, oxidative markers (i.e. ketamine-induced decrease and increase in GSH levels and TBARS content, respectively) as well as nitrite levels in the striatum. These data provide a rationale for evaluating minocycline as a novel psychotropic agent and suggest that its mechanism of action includes antioxidant and nitrergic systems.