Catching up on schizophrenia: natural history and neurobiology

The cannabinoid receptor 1 associates with NMDA receptors to produce glutamatergic hypofunction: implications in psychosis and schizophrenia

The endocannabinoid system is widespread throughout the central nervous system and its type 1 receptor (CB1) plays a crucial role in preventing the neurotoxicity caused by activation of glutamate N-methyl-D-aspartate receptors (NMDARs). Indeed, it is the activity of NMDARs themselves that provides the demands on the endogenous cannabinoids in order to control their calcium currents. Therefore, a physiological role of this system is to maintain NMDAR activity within safe limits, thereby protecting neural cells from excitotoxicity. Thus, cannabinoids may be able to control NMDAR overactivation-related neural dysfunctions; however, the major obstacles to the therapeutic utilization of these compounds are their psychotropic effects and negative influence on cognitive performance. Studies in humans have indicated that abuse of smoked cannabis can promote psychosis and even circumstantially precipitate symptoms of schizophrenia, although the latter appears to require a prior vulnerability in the individual. It is possible that cannabinoids provoke psychosis/schizophrenia reflecting a mechanism common to neuroprotection: the reduction of NMDAR activity. Cannabinoids are proposed to produce such effect by reducing the pre-synaptic release of glutamate or interfering with post-synaptic NMDAR-regulated signaling pathways. The efficacy of such control requires the endocannabinoid system to apply its negative influence in a manner that is proportional to the strength of NMDAR signaling. Thus, cannabinoids acting at the wrong time or exerting an inappropriate influence on their receptors may cause NMDAR hypofunction. The purpose of the present review is to draw the attention of the reader to the newly described functional and physical CB1-NMDAR association, which may elucidate the scenario required for the rapid and efficacious control of NMDAR activity. Whether alterations in these mechanisms may increase NMDAR hypofunction leading to vulnerability to schizophrenia will be outlined.

Reduced visual surround suppression in schizophrenia shown by measuring contrast detection thresholds

Visual perception in schizophrenia is attracting a broad interest given the deep knowledge that we have about the visual system in healthy populations. One example is the class of effects known collectively as visual surround suppression. For example, the visibility of a grating located in the visual periphery is impaired by the presence of a surrounding grating of the same spatial frequency and orientation. Previous studies have suggested abnormal visual surround suppression in patients with schizophrenia. Given that schizophrenia patients have cortical alterations including hypofunction of NMDA receptors and reduced concentration of GABA neurotransmitter, which affect lateral inhibitory connections, then they should be relatively better than controls at detecting visual stimuli that are usually suppressed. We tested this hypothesis by measuring contrast detection thresholds using a new stimulus configuration. We tested two groups: 21 schizophrenia patients and 24 healthy subjects. Thresholds were obtained using Bayesian staircases in a four-alternative forced-choice detection task where the target was a grating within a 3∘ Butterworth window that appeared in one of four possible positions at 5∘ eccentricity. We compared three conditions, (a) target with no-surround, (b) target embedded within a surrounding grating of 20∘ diameter and 25% contrast with same spatial frequency and orthogonal orientation, and (c) target embedded within a surrounding grating with parallel (same) orientation. Previous results with healthy populations have shown that contrast thresholds are lower for orthogonal and no-surround (NS) conditions than for parallel surround (PS). The log-ratios between parallel and NS thresholds are used as an index quantifying visual surround suppression. Patients performed poorly compared to controls in the NS and orthogonal-surround conditions. However, they performed as well as controls when the surround was parallel, resulting in significantly lower suppression indices in patients. To examine whether the difference in suppression was driven by the lower NS thresholds for controls, we examined a matched subgroup of controls and patients, selected to have similar thresholds in the NS condition. Patients performed significantly better in the PS condition than controls. This analysis therefore indicates that a PS raised contrast thresholds less in patients than in controls. Our results support the hypothesis that inhibitory connections in early visual cortex are impaired in schizophrenia patients.

Antenatal glucocorticoid treatment induces adaptations in adult midbrain dopamine neurons, which underpin sexually dimorphic behavioral resilience

We demonstrated previously that antenatal glucocorticoid treatment (AGT, gestational days 16-19) altered the size and organization of the adult rat midbrain dopaminergic (DA) populations. Here we investigated the consequences of these AGT-induced cytoarchitectural disturbances on indices of DA function in adult rats. We show that in adulthood, enrichment of striatal DA fiber density paralleled AGT-induced increases in the numbers of midbrain DA neurons, which retained normal basal electrophysiological properties. This was co-incident with changes in (i) striatal D2-type receptor levels (increased, both sexes); (ii) D1-type receptor levels (males decreased; females increased); (iii) DA transporter levels (males increased; females decreased) in striatal regions; and (iv) amphetamine-induced mesolimbic DA release (males increased; females decreased). However, despite these profound, sexually dimorphic changes in markers of DA neurotransmission, in-utero glucocorticoid overexposure had a modest or no effect on a range of conditioned and unconditioned appetitive behaviors known to depend on mesolimbic DA activity. These findings provide empirical evidence for enduring AGT-induced adaptive mechanisms within the midbrain DA circuitry, which preserve some, but not all, functions, thereby casting further light on the vulnerability of these systems to environmental perturbations. Furthermore, they demonstrate these effects are achieved by different, often opponent, adaptive mechanisms in males and females, with translational implications for sex biases commonly found in midbrain DA-associated disorders.

Connectivity, pharmacology, and computation: toward a mechanistic understanding of neural system dysfunction in schizophrenia

Neuropsychiatric diseases such as schizophrenia and bipolar illness alter the structure and function of distributed neural networks. Functional neuroimaging tools have evolved sufficiently to reliably detect system-level disturbances in neural networks. This review focuses on recent findings in schizophrenia and bipolar illness using resting-state neuroimaging, an advantageous approach for biomarker development given its ease of data collection and lack of task-based confounds. These benefits notwithstanding, neuroimaging does not yet allow the evaluation of individual neurons within local circuits, where pharmacological treatments ultimately exert their effects. This limitation constitutes an important obstacle in translating findings from animal research to humans and from healthy humans to patient populations. Integrating new neuroscientific tools may help to bridge some of these gaps. We specifically discuss two complementary approaches. The first is pharmacological manipulations in healthy volunteers, which transiently mimic some cardinal features of psychiatric conditions. We specifically focus on recent neuroimaging studies using the NMDA receptor antagonist, ketamine, to probe glutamate synaptic dysfunction associated with schizophrenia. Second, we discuss the combination of human pharmacological imaging with biophysically informed computational models developed to guide the interpretation of functional imaging studies and to inform the development of pathophysiologic hypotheses. To illustrate this approach, we review clinical investigations in addition to recent findings of how computational modeling has guided inferences drawn from our studies involving ketamine administration to healthy subjects. Thus, this review asserts that linking experimental studies in humans with computational models will advance to effort to bridge cellular, systems, and clinical neuroscience approaches to psychiatric disorders.

The neuroimmunology of schizophrenia

Schizophrenia (SCZ) is a polygenic, multi-factorial disorder and a definitive understanding of its pathophysiology has been lacking since it was first described more than a century ago. The predominant pharmacological approach used to treat SCZ is the use of dopamine receptor antagonists. The fact that many patients remain symptomatic, despite complying with medication regimens, emphasises the need for a more encompassing explanation for both the causes and treatment of SCZ. Recent neuroanatomical, neurobiological, environmental and genetic studies have revived the idea that inflammatory pathways are involved in the pathogenesis of SCZ. These new insights have emerged from multiple lines of evidence, including the levels of inflammatory proteins in the central nervous system of patients with SCZ and animal models. This review focuses on aberrant inflammatory mechanisms present both before and during the onset of the psychotic symptoms that characterise SCZ and discusses recent research into adjunctive immune system modulating therapies for its more effective treatment.

Expression of 5-HT2A receptors in prefrontal cortex pyramidal neurons projecting to nucleus accumbens. Potential relevance for atypical antipsychotic action

The prefrontal cortex (PFC) is involved in higher brain functions altered in schizophrenia. Classical antipsychotic drugs modulate information processing in cortico-limbic circuits via dopamine D2 receptor blockade in nucleus accumbens (NAc) whereas atypical antipsychotic drugs preferentially target cortical serotonin (5-HT) receptors. The brain networks involved in the therapeutic action of atypical drugs are not fully understood. Previous work indicated that medial PFC (mPFC) pyramidal neurons projecting to ventral tegmental area express 5-HT2A receptors suggesting that atypical antipsychotic drugs modulate dopaminergic activity distally, via 5-HT2A receptor (5-HT2A-R) blockade in PFC. Since the mPFC also projects heavily to NAc, we examined whether NAc-projecting pyramidal neurons also express 5-HT2A-R. Using a combination of retrograde tracing experiments and in situ hybridization we report that a substantial proportion of mPFC-NAc pyramidal neurons in rat brain express 5-HT2A-R mRNA in a layer- and area-specific manner (up to 68% in layer V of contralateral cingulate). The functional relevance of 5-HT2A-R to modulate mPFC-NAc projections was examined in dual-probe microdialysis experiments. The application of the preferential 5-HT2A-R agonist DOI into mPFC enhanced glutamate release locally (+66 ± 18%) and in NAc (+74 ± 12%) indicating that cortical 5-HT2A-R activation augments glutamatergic transmission in NAc. Since NAc integrates glutamatergic and dopaminergic inputs, blockade of 5-HT2A-R by atypical drugs may reduce cortical excitatory inputs onto GABAergic neurons of NAc, adding to dopamine D2 receptor blockade. Together with previous observations, the present results suggest that atypical antipsychotic drugs may control the activity of the mesolimbic pathway at cell body and terminal level.

Disruption of thalamocortical activity in schizophrenia models: relevance to antipsychotic drug action

Non-competitive NMDA receptor antagonists are widely used as pharmacological models of schizophrenia due to their ability to evoke the symptoms of the illness. Likewise, serotonergic hallucinogens, acting on 5-HT(2A) receptors, induce perceptual and behavioural alterations possibly related to psychotic symptoms. The neurobiological basis of these alterations is not fully elucidated. Data obtained in recent years revealed that the NMDA receptor antagonist phencyclidine (PCP) and the serotonergic hallucinogen 1-(2,5-dimethoxy-4-iodophenyl-2-aminopropane; DOI) produce a series of common actions in rodent prefrontal cortex (PFC) that may underlie psychotomimetic effects. Hence, both agents markedly disrupt PFC function by altering pyramidal neuron discharge (with an overall increase) and reducing the power of low frequency cortical oscillations (LFCO; < 4 Hz). In parallel, PCP increased c-fos expression in excitatory neurons of various cortical areas, the thalamus and other subcortical structures, such as the amygdala. Electrophysiological studies revealed that PCP altered similarly the function of the centromedial and mediodorsal nuclei of the thalamus, reciprocally connected with PFC, suggesting that its psychotomimetic properties are mediated by an alteration of thalamocortical activity (the effect of DOI was not examined in the thalamus). Interestingly, the observed effects were prevented or reversed by the antipsychotic drugs clozapine and haloperidol, supporting that the disruption of PFC activity is intimately related to the psychotomimetic activity of these agents. Overall, the present experimental model can be successfully used to elucidate the neurobiological basis of schizophrenia symptoms and to examine the potential antipsychotic activity of new drugs in development.

Anatomical and functional brain abnormalities in drug-naive first-episode schizophrenia

OBJECTIVE

The authors sought to explore whether anatomical and functional brain deficits are present in similar or different brain regions early in the course of schizophrenia, before antipsychotic treatment, and whether these deficits are more severe or otherwise different in patients with prominent negative symptoms.

METHOD

A total of 100 drug-naive first-episode schizophrenia patients and 100 matched healthy comparison subjects underwent structural and resting-state functional MRI scanning. Gray matter volume and amplitude of low-frequency fluctuations during resting-state functional studies were measured.

RESULTS

Group comparisons of gray matter volume showed significant differences mainly in thalamo-cortical networks, while alterations in the amplitude of low-frequency fluctuations were observed in fronto-parietal and default mode networks. Thus, different brain regions had alterations in gray matter volume and resting state physiology. These changes did not correlate with the duration of untreated illness, nor with acute clinical symptom severity. Patients with prominent negative symptoms had greater regional alterations in brain anatomy, particularly in the left dorsolateral prefrontal cortex, while the pattern of functional alterations was unrelated to severity of negative symptoms.

CONCLUSIONS

Anatomical and resting-state functional deficits were observed in different brain regions, indicating that anatomical and functional brain abnormalities are significantly dissociated in the early course of schizophrenia. The lack of association of these abnormalities with illness duration and episode severity suggests that these anatomical and functional changes may be early-evolving features of the illness that are relatively stable early in the course of illness. The different structural deficits of regional gray matter observed in patients with prominent negative symptoms may provide unique insight into the early regional neuropathology of this symptom dimension in schizophrenia.

Peptide POP inhibitors for the treatment of the cognitive symptoms of schizophrenia

Schizophrenia is a serious life-long disease that affects a significant part of the adult population. Although there is considerably effective medication for the positive symptoms of the disease, none are available for the associated cognitive deficits. These deficits are a core feature of schizophrenia, and they severely impair the functionality and social integration of patients. POP is a promising target for the treatment of the cognitive deficits of schizophrenia. Inhibitors of this peptidase show cognition-enhancing properties, act through a complex mechanism and have suitable pharmacological properties. Nevertheless, several studies must be carried out in order to improve the design and clinical evaluation of these substances. Permeability to the brain, appropriate animal models and suitable indications are the main issues that must be addressed. However, current information supports the potential of POP as an interesting drug target for the treatment of the cognitive deficits related to schizophrenia.

Altered oxygen metabolism associated to neurogenesis of induced pluripotent stem cells derived from a schizophrenic patient

Schizophrenia has been defined as a neurodevelopmental disease that causes changes in the process of thoughts, perceptions, and emotions, usually leading to a mental deterioration and affective blunting. Studies have shown altered cell respiration and oxidative stress response in schizophrenia; however, most of the knowledge has been acquired from postmortem brain analyses or from nonneural cells. Here we describe that neural cells, derived from induced pluripotent stem cells generated from skin fibroblasts of a schizophrenic patient, presented a twofold increase in extramitochondrial oxygen consumption as well as elevated levels of reactive oxygen species (ROS), when compared to controls. This difference in ROS levels was reverted by the mood stabilizer valproic acid. Our model shows evidence that metabolic changes occurring during neurogenesis are associated with schizophrenia, contributing to a better understanding of the development of the disease and highlighting potential targets for treatment and drug screening.

GABA transporter-1 deficiency confers schizophrenia-like behavioral phenotypes

The mechanism underlying the pathogenesis of schizophrenia remains poorly understood. The hyper-dopamine and hypo-NMDA receptor hypotheses have been the most enduring ideas. Recently, emerging evidence implicates alterations of the major inhibitory system, GABAergic neurotransmission in the schizophrenic patients. However, the pathophysiological role of GABAergic system in schizophrenia still remains dubious. In this study, we took advantage of GABA transporter 1 (GAT1) knockout (KO) mouse, a unique animal model with elevated ambient GABA, to study the schizophrenia-related behavioral abnormalities. We found that GAT1 KO mice displayed multiple behavioral abnormalities related to schizophrenic positive, negative and cognitive symptoms. Moreover, GAT1 deficiency did not change the striatal dopamine levels, but significantly enhanced the tonic GABA currents in prefrontal cortex. The GABA(A) receptor antagonist picrotoxin could effectively ameliorate several behavioral defects of GAT1 KO mice. These results identified a novel function of GAT1, and indicated that the elevated ambient GABA contributed critically to the pathogenesis of schizophrenia. Furthermore, several commonly used antipsychotic drugs were effective in treating the locomotor hyperactivity in GAT1 KO mice, suggesting the utility of GAT1 KO mice as an alternative animal model for studying schizophrenia pathogenesis and developing new antipsychotic drugs.

The atypical antipsychotic risperidone reverses the recognition memory deficits induced by post-weaning social isolation in rats

RATIONALE

Rearing rats in isolation from weaning is an established preclinical neurodevelopmental model which induces behavioural deficits with apparent translational relevance to some core symptoms of schizophrenia.

OBJECTIVE

This study evaluated the ability of the atypical antipsychotic risperidone to reverse behavioural deficits induced by post-weaning social isolation of rat pups and to further characterise the predictive validity of this model.

METHOD

Forty-five male Lister hooded rats were housed in groups of 3-4 (n = 16) or singly (n = 29) for 4 weeks immediately after weaning on postnatal day (PND) 22-24. On PND 51, novel cage-induced locomotor activity (LMA) was assessed to subdivide rats into groups balanced for behavioural response. On PNDs 58, 59, 65 and 72, rats received either vehicle (1 ml/kg; i.p.) or risperidone (0.2 or 0.5 mg/kg; i.p.) 30 min prior to testing in LMA, novel object discrimination (NOD), prepulse inhibition (PPI) of acoustic startle and conditioned emotional response (CER) learning paradigms, respectively.

RESULTS

Isolation rearing had no effect on PPI, but produced LMA hyperactivity and impaired NOD and CER compared to group-housed controls. Risperidone caused a dose-dependent reduction in LMA, irrespective of rearing condition, but selectively reversed the NOD deficit in isolation-reared rats. Risperidone did not reverse the isolation rearing-induced CER deficit.

CONCLUSIONS

Similar to its clinical profile, risperidone only partially reverses the schizophrenic symptomology; since it reversed some, but not all, of the learning and memory deficits induced by post-weaning isolation, the isolation rearing model may be useful to predict antipsychotic activity of novel therapeutic agents.

Expression of α(1)-adrenergic receptors in rat prefrontal cortex: cellular co-localization with 5-HT(2A) receptors

The prefrontal cortex (PFC) is involved in behavioural control and cognitive processes that are altered in schizophrenia. The brainstem monoaminergic systems control PFC function, yet the cells/networks involved are not fully known. Serotonin (5-HT) and norepinephrine (NE) increase PFC neuronal activity through the activation of α(1)-adrenergic receptors (α(1)ARs) and 5-HT(2A) receptors (5-HT(2A)Rs), respectively. Neurochemical and behavioural interactions between these receptors have been reported. Further, classical and atypical antipsychotic drugs share nm in vitro affinity for α(1)ARs while having preferential affinity for D(2) and 5-HT(2A)Rs, respectively. Using double in situ hybridization we examined the cellular expression of α(1)ARs in pyramidal (vGluT1-positive) and GABAergic (GAD(65/67)-positive) neurons in rat PFC and their co-localization with 5-HT(2A)Rs. α(1)ARs are expressed by a high proportion of pyramidal (59-85%) and GABAergic (52-79%) neurons. The expression in pyramidal neurons exhibited a dorsoventral gradient, with a lower percentage of α(1)AR-positive neurons in infralimbic cortex compared to anterior cingulate and prelimbic cortex. The expression of α(1A), α(1B) and α(1D) adrenergic receptors was segregated in different layers and subdivisions. In all them there is a high co-expression with 5-HT(2A)Rs (∼80%). These observations indicate that NE controls the activity of most PFC pyramidal neurons via α(1)ARs, either directly or indirectly, via GABAergic interneurons. Antipsychotic drugs can thus modulate the activity of PFC via α(1)AR blockade. The high co-expression with 5-HT(2A)Rs indicates a convergence of excitatory serotonergic and noradrenergic inputs onto the same neuronal populations. Moreover, atypical antipsychotics may exert a more powerful control of PFC function through the simultaneous blockade of α(1)ARs and 5-HT(2A)Rs.

A new perspective for schizophrenia: TAAR1 agonists reveal antipsychotic- and antidepressant-like activity, improve cognition and control body weight

Schizophrenia is a chronic, severe and highly complex mental illness. Current treatments manage the positive symptoms, yet have minimal effects on the negative and cognitive symptoms, two prominent features of the disease with critical impact on the long-term morbidity. In addition, antipsychotic treatments trigger serious side effects that precipitate treatment discontinuation. Here, we show that activation of the trace amine-associated receptor 1 (TAAR1), a modulator of monoaminergic neurotransmission, represents a novel therapeutic option. In rodents, activation of TAAR1 by two novel and pharmacologically distinct compounds, the full agonist RO5256390 and the partial agonist RO5263397, blocks psychostimulant-induced hyperactivity and produces a brain activation pattern reminiscent of the antipsychotic drug olanzapine, suggesting antipsychotic-like properties. TAAR1 agonists do not induce catalepsy or weight gain; RO5263397 even reduced haloperidol-induced catalepsy and prevented olanzapine from increasing body weight and fat accumulation. Finally, TAAR1 activation promotes vigilance in rats and shows pro-cognitive and antidepressant-like properties in rodent and primate models. These data suggest that TAAR1 agonists may provide a novel and differentiated treatment of schizophrenia as compared with current medication standards: TAAR1 agonists may improve not only the positive symptoms but also the negative symptoms and cognitive deficits, without causing adverse effects such as motor impairments or weight gain.

D-serine as a gliotransmitter and its roles in brain development and disease

The development of new techniques to study glial cells has revealed that they are active participants in the development of functional neuronal circuits. Calcium imaging studies demonstrate that glial cells actively sense and respond to neuronal activity. Glial cells can produce and release neurotransmitter-like molecules, referred to as gliotransmitters, that can in turn influence the activity of neurons and other glia. One putative gliotransmitter, D-serine is believed to be an endogenous co-agonist for synaptic N-methyl-D-aspartate receptors (NMDARs), modulating synaptic transmission and plasticity mediated by this receptor. The observation that D-serine levels in the mammalian brain increase during early development, suggests a possible role for this gliotransmitter in normal brain development and circuit refinement. In this review we will examine the data that D-serine and its associated enzyme serine racemase are developmentally regulated. We will consider the evidence that D-serine is actively released by glial cells and examine the studies that have implicated D-serine as a critical player involved in regulating NMDAR-mediated synaptic transmission and neuronal migration during development. Furthermore, we will consider how dysregulation of D-serine may play an important role in the etiology of neurological and psychiatric diseases.

Management of schizophrenia: clinical experience with asenapine

Schizophrenia is a chronic brain disorder comprising a range of clinical features, including positive and negative symptoms, cognitive dysfunction and mood symptoms (particularly depression and anxiety). The management of schizophrenia requires effective short- and long-term treatment with antipsychotic medication that is effective across these symptom domains, while being well tolerated over the long term. Asenapine is the first tetracyclic atypical antipsychotic to be licensed in the USA and several other countries outside Europe for the acute and maintenance treatment of schizophrenia in adults. It has a unique receptor-binding profile and a broad range of therapeutic effects. Since clinical trials are conducted under strict conditions in tightly defined patient populations, evidence of an agent's efficacy and tolerability under 'real-world' clinical practice conditions is also required. As in clinical trials, real-life case reports demonstrate that asenapine is effective in treating the positive symptoms of schizophrenia, both in the acute setting and for relapse prevention. It is also effective in treating negative symptoms and shows promise in the treatment of depressive symptoms associated with schizophrenia. Asenapine has a favourable tolerability profile, having a minimal impact on weight and metabolic parameters. As such, asenapine is valuable option for the treatment of schizophrenia in adults.

Rac GEF Dock4 interacts with cortactin to regulate dendritic spine formation

Rac GEF Dock4, recently reported as a candidate genetic risk factor for autism, dyslexia, and schizophrenia, is highly concentrated in dendritic spines in hippocampal neurons and is implicated in spine formation through interaction with the actin-binding protein cortactin.

In neuronal development, dendritic spine formation is important for the establishment of excitatory synaptic connectivity and functional neural circuits. Developmental deficiency in spine formation results in multiple neuropsychiatric disorders. Dock4, a guanine nucleotide exchange factor (GEF) for Rac, has been reported as a candidate genetic risk factor for autism, dyslexia, and schizophrenia. We previously showed that Dock4 is expressed in hippocampal neurons. However, the functions of Dock4 in hippocampal neurons and the underlying molecular mechanisms are poorly understood. Here we show that Dock4 is highly concentrated in dendritic spines and implicated in spine formation via interaction with the actin-binding protein cortactin. In cultured neurons, short hairpin RNA (shRNA)–mediated knockdown of Dock4 reduces dendritic spine density, which is rescued by coexpression of shRNA-resistant wild-type Dock4 but not by a GEF-deficient mutant of Dock4 or a truncated mutant lacking the cortactin-binding region. On the other hand, knockdown of cortactin suppresses Dock4-mediated spine formation. Taken together, the results show a novel and functionally important interaction between Dock4 and cortactin for regulating dendritic spine formation via activation of Rac.

The developing utility of zebrafish models for cognitive enhancers research

Whereas cognitive impairment is a common symptom in multiple brain disorders, predictive and high-throughput animal models of cognition and behavior are becoming increasingly important in the field of translational neuroscience research. In particular, reliable models of the cognitive deficits characteristic of numerous neurobehavioral disorders such as Alzheimer’s disease and schizophrenia have become a significant focus of investigation. While rodents have traditionally been used to study cognitive phenotypes, zebrafish (Danio rerio) are gaining popularity as an excellent model to complement current translational neuroscience research. Here we discuss recent advances in pharmacological and genetic approaches using zebrafish models to study cognitive impairments and to discover novel cognitive enhancers and neuroprotective mechanisms.

Ontogenetic influence on rat susceptibility to lindane seizure after pretreatment with phencyclidine

The aim of the study was to determine the effects of early postnatal PCP treatment on the sensitivity of pubertal and adult rats to lindane proepileptogenic effects. Rat pups were treated with NaCl (0.9%) or PCP (10 mg/kg) at postnatal days 2, 6, 9 and 12. One control (NaCl-35) and one experimental (PCP-35) group have received lindane (4 mg/kg) at postnatal day 35, while others received lindane at postnatal day 65 (NaCl-65 and PCP-65). One week prior to lindane treatment three gold-plated EEG electrodes were implanted. Pubertal rats had significantly shorter latency time. After lindane, a prompt increase in power spectral density seen in PCP-treated groups vs. control was evident earlier in PCP-65 rats. The theta waves were significantly increased in PCP-35 and alpha rhythm in PCP-65 rats, when compared with corresponding controls. Postnatal PCP treatment increases the synchronization of brain electrical activity, thus contributing to the increased susceptibility to lindane.

Brain RGS4 and RGS10 protein expression in schizophrenia and depression. Effect of drug treatment

RATIONALE

Regulator of G-protein signaling (RGS) proteins, RGS4 and RGS10, may be involved in the pathophysiology of schizophrenia. RGS4 has attracted special interest since the reports of genetic association between SNPs in RGS4 and schizophrenia. However, there is no information about the subcellular distribution of RGS4 and RGS10 proteins in psychiatric disorders.

OBJECTIVES

Plasma membrane RGS4 and cytosolic RGS10 protein immunoreactivity in prefrontal cortex from schizophrenic subjects (n = 25), non-diagnosed suicides (n = 13), and control subjects (n = 35), matched by age, gender, and postmortem delay, was analyzed by western blot. A second group of depressed subjects (n = 25) and control subjects (n = 25) was evaluated. The effect of the antipsychotic or antidepressant treatments was also assessed.

RESULTS

No significant differences in plasma membrane RGS4 and cytosolic RGS10 protein expression were observed between schizophrenic subjects, non-diagnosed suicides, and control subjects. However, RGS4 immunoreactivity was significantly higher (Δ = 33 ± 10 %, p < 0.05) in the antipsychotic-treated subgroup (n = 12) than in the antipsychotic-free subgroup (n = 13). Immunodensities of plasma membrane RGS4 and cytosolic RGS10 proteins did not differ between depressed and matched control subjects.

CONCLUSIONS

Expression of RGS4 and RGS10 proteins at their predominant subcellular location was studied in the postmortem brain of subjects with psychiatric disorders. The results suggest unaltered membrane RGS4 and cytosolic RGS10 proteins levels in schizophrenia and major depression. Antipsychotic treatment seems to increase membrane RGS4 immunoreactivity. Further studies are needed to elucidate RGS4 and RGS10 functional status.

The application of nonlinear Dynamic Causal Modelling for fMRI in subjects at high genetic risk of schizophrenia

Nonlinear Dynamic Causal Modelling (DCM) for fMRI provides computational modelling of gating mechanisms at the neuronal population level. It allows for estimations of connection strengths with nonlinear modulation within task-dependent networks. This paper presents an application of nonlinear DCM in subjects at high familial risk of schizophrenia performing the Hayling Sentence Completion Task (HSCT). We analysed scans of 19 healthy controls and 46 subjects at high familial risk of schizophrenia, which included 26 high risk subjects without psychotic symptoms and 20 subjects with psychotic symptoms. The activity-dependent network consists of the intra parietal cortex (IPS), inferior frontal gyrus (IFG), middle temporal gyrus (MTG), anterior cingulate cortex (ACC) and the mediodorsal (MD) thalamus. The connections between the MD thalamus and the IFG were gated by the MD thalamus. We used DCM to investigate altered connection strength of these connections. Bayesian Model Selection (BMS) at the group and family level was used to compare the optimal bilinear and nonlinear models. Bayesian Model Averaging (BMA) was used to assess the connection strengths with the gating from the MD thalamus and the IFG. The nonlinear models provided the better explanation of the data. Furthermore, the BMA analysis showed significantly lower connection strength of the thalamocortical connection with nonlinear modulation from the MD thalamus in high risk subjects with psychotic symptoms and those who subsequently developed schizophrenia. These findings demonstrate that nonlinear DCM provides a method to investigate altered connectivity at the level of neural circuits. The reduced connection strength with thalamic gating may be a neurobiomarker implicated in the development of psychotic symptoms. This study suggests that nonlinear DCM could lead to new insights into functional and effective dysconnection at the network level in subjects at high familial risk.

BDNF-TrkB signaling and neuroprotection in schizophrenia

Neurotrophins such as brain-derived neurotropic factor (BDNF), play critical role in neuronal survival, synaptic plasticity and cognitive functions. BDNF is known to mediate its action through various intracellular signaling pathways triggered by activation of tyrosine kinase receptor B (TrkB). Evidence from clinical as well pre-clinical studies indicate alterations in BDNF signaling in schizophrenia. Moreover, several antipsychotic drugs have time-dependent effects on BDNF levels in both schizophrenia subjects and animal models of schizophrenia. Given the emerging interest in neuroplasticity in schizophrenia understanding the neuroprotective and cell survival roles of BDNF signaling will enhance our knowledge of its diverse effects, which may lead to more effective treatments for schizophrenia. This article will present an overview of recent findings on the role of BDNF signaling in the pathophysiology and treatment of schizophrenia, with a special focus on its neuroprotective effects.

Association between polymorphisms in the genes for tumor suppressor protein p53 and its regulator NAD(P)H: quinone oxidoreductase 1 (NQO1) and schizophrenia in a Syrian study cohort

BACKGROUND AND AIMS

The contribution of genetic factors to the susceptibility for developing schizophrenia is well established. Several hypotheses have been developed in an attempt to identify the pathophysiological mechanisms in schizophrenia, with several findings implicating an important role for apoptosis. A limited number of studies investigated the effects of polymorphisms in apoptotic genes on the susceptibility to schizophrenia in different ethnic groups, with none involving an Arab population. The aim of the present study was to investigate the association between multiple polymorphisms in genes for the central apoptotic protein p53 and its regulator NQO1 and the susceptibility for developing schizophrenia in an Arab population from Syria.

METHODS

The studied polymorphisms included exon 4 G>C Arg72Pro (rs1042522), IVS3 16 bp Del/Ins (rs17878362), and MspI IVS6+62A>G (rs1625895) of the TP53 gene, and C609T of the NQO1 gene. The study cohort consisted of 90 patients and 144 healthy controls. Association with each of the four polymorphisms was tested under numerous genetic models. The four polymorphisms were genotyped simultaneously using a quadruplex Tetra-Primer ARMS-PCR method described earlier. The combined effects of polymorphisms in NQO1 and TP53 genes were examined.

RESULTS

No statistically significant association was found for any of the four polymorphisms.

CONCLUSIONS

Our results do not support an association between the studied polymorphisms and schizophrenia in the Syrian population.

Altered cortical GABA neurotransmission in schizophrenia: insights into novel therapeutic strategies

Altered markers of cortical GABA neurotransmission are among the most consistently observed abnormalities in postmortem studies of schizophrenia. The altered markers are particularly evident between the chandelier class of GABA neurons and their synaptic targets, the axon initial segment (AIS) of pyramidal neurons. For example, in the dorsolateral prefrontal cortex of subjects with schizophrenia immunoreactivity for the GABA membrane transporter is decreased in presynaptic chandelier neuron axon terminals, whereas immunoreactivity for the GABAA receptor α2 subunit is increased in postsynaptic AIS. Both of these molecular changes appear to be compensatory responses to a presynaptic deficit in GABA synthesis, and thus could represent targets for novel therapeutic strategies intended to augment the brain's own compensatory mechanisms. Recent findings that GABA inputs from neocortical chandelier neurons can be powerfully excitatory provide new ideas about the role of these neurons in the pathophysiology of cortical dysfunction in schizophrenia, and consequently in the design of pharmacological interventions.

Metabotropic glutamate receptor 5 in the pathology and treatment of schizophrenia

Metabotropic glutamate receptor 5 (mGluR5) potentiates the NMDA receptor (NMDAR) in brain regions implicated in schizophrenia, making it a viable therapeutic target for the treatment of this disorder. mGluR5 positive allosteric modulators may represent a valuable novel strategy for schizophrenia treatment, given the favourable profile of effects in preclinical paradigms. However it remains unclear whether mGluR5 also plays a causal or epiphenomenal role in NMDAR dysfunction in schizophrenia. Animal and cellular data suggest involvement of mGluR5, whilst post-mortem human studies remain inconclusive. This review will explore the molecular, animal and human data to support and refute the involvement of mGluR5 in the pathology of schizophrenia. Furthermore, this review will discuss the potential of mGluR5 modulators in the therapy of schizophrenia as well as aspects of mGluR5 that require further characterisation.

Pluripotent stem cells as a model to study oxygen metabolism in neurogenesis and neurodevelopmental disorders

Reactive oxygen species (ROS) and oxygen (O2) have been implicated in neurogenesis and self-renewal of neural progenitor cells (NPCs). On the other hand, oxidative unbalance, either by an impairment of antioxidant defenses or by an intensified production of ROS, is increasingly related to risk factors of neurodevelopmental disorders, such as schizophrenia. In this scenario, human induced pluripotent stem cells (hiPSCs) emerged as an interesting platform for the study of cellular and molecular aspects of this mental disorder, by complementing other experimental models, with exclusive advantages such as the recapitulation of brain development. Herein we discuss the role of O2/ROS signaling for neuronal differentiation and how its unbalance could be related to neurodevelopmental disorders, such as schizophrenia. Identifying the role of O2/ROS in neurogenesis as well as tackling oxidative stress and its disturbances in schizophrenic patients' derived cells will provide an interesting opportunity for the study of neural stem cells differentiation and neurodevelopmental disorders.

Preclinical (1)H-MRS neurochemical profiling in neurological and psychiatric disorders

The ongoing development of animal models of neurological and psychiatric disorders in combination with the development of advanced nuclear magnetic resonance (NMR) techniques and instrumentation has led to increased use of in vivo proton NMR spectroscopy ((1)H-MRS) for neurochemical analyses. (1)H-MRS is one of only a few analytical methods that can assay in vivo and longitudinal neurochemical changes associated with neurological and psychiatric diseases, with the added advantage of being a technique that can be utilized in both preclinical and clinical studies. In this review, recent progress in the use of (1)H-MRS to investigate animal models of neurological and psychiatric disorders is summarized with examples from the literature and our own work.

Cortico-subcortical neuromodulation involved in the amelioration of prepulse inhibition deficits in dopamine transporter knockout mice

Prepulse inhibition (PPI) deficits are among the most reproducible phenotypic markers found in schizophrenic patients. We recently reported that nisoxetine, a selective norepinephrine transporter (NET) inhibitor, reversed the PPI deficits that have been identified in dopamine transporter (DAT) knockout (KO) mice. However, the mechanisms underlying nisoxetine-induced PPI recovery in DAT KO mice were unclear in previous experiments. To clarify these mechanisms, PPI was tested after microinjections of nisoxetine into the medial prefrontal cortex (mPFc) or nucleus accumbens (NAc) in wildtype (WT) and DAT KO mice. c-Fos immunohistochemistry provided an indicator of neural activation. Multiple-fluorescent-labeling procedures and the retrograde tracer fluorogold were employed to identify nisoxetine-activated neurons and circuits. Systemic nisoxetine activated the mPFc, the NAc shell, the basolateral amygdala, and the subiculum. Infusions of nisoxetine into the mPFc reversed PPI deficits in DAT KO mice, but produced no changes in WT mice, while infusion of nisoxetine into the NAc had no effect on PPI in both WT and DAT KO mice. Experiments using multiple-fluorescent labeling/fluorogold revealed that nisoxetine activates presumed glutamatergic pyramidal cells that project from the mPFc to the NAc. Activated glutamatergic projections from the mPFc to the NAc appear to have substantial roles in the ability of a NET inhibitor to normalize PPI deficits in DAT KO. Thus, this data suggest that selective NET inhibitors such as nisoxetine might improve information processing deficits in schizophrenia via regulation of cortico-subcortical neuromodulation.

Schizophrenia shows a unique metabolomics signature in plasma

Schizophrenia is a severe complex mental disorder affecting 0.5-1% of the world population. To date, diagnosis of the disease is mainly based on personal and thus subjective interviews. The underlying molecular mechanism of schizophrenia is poorly understood. Using targeted metabolomics we quantified and compared 103 metabolites in plasma samples from 216 healthy controls and 265 schizophrenic patients, including 52 cases that do not take antipsychotic medication. Compared with healthy controls, levels of five metabolites were found significantly altered in schizophrenic patients (P-values ranged from 2.9 × 10(-8) to 2.5 × 10(-4)) and in neuroleptics-free probands (P-values ranging between 0.006 and 0.03), respectively. These metabolites include four amino acids (arginine, glutamine, histidine and ornithine) and one lipid (PC ae C38:6) and are suggested as candidate biomarkers for schizophrenia. To explore the genetic susceptibility on the associated metabolic pathways, we constructed a molecular network connecting these five aberrant metabolites with 13 schizophrenia risk genes. Our result implicated aberrations in biosynthetic pathways linked to glutamine and arginine metabolism and associated signaling pathways as genetic risk factors, which may contribute to patho-mechanisms and memory deficits associated with schizophrenia. This study illustrated that the metabolic deviations detected in plasma may serve as potential biomarkers to aid diagnosis of schizophrenia.

Ketamine-enhanced immobility in forced swim test: a possible animal model for the negative symptoms of schizophrenia

Schizophrenia is a chronic and highly complex psychiatric disorder characterised by cognitive dysfunctions, negative and positive symptoms. The major challenge in schizophrenia research is lack of suitable animal models that mimic the core behavioural aspects and symptoms of this devastating psychiatric disorder. In this study, we used classical and atypical antipsychotic drugs to examine the predictive validity of ketamine-enhanced immobility in forced swim test (FST) as a possible animal model for the negative symptoms of schizophrenia. We also evaluated the effects of a selective serotonin reuptake inhibitor (SSRI) on the ketamine-enhanced immobility in FST. Repeated administration of a subanaesthetic dose of ketamine (30 mg kg(-1), i.p., daily for 5 days) enhanced the duration of immobility in FST 24 h after the final injection. The effect, which persisted for at least 21 days after withdrawal of the drug, was neither observed by single treatment with ketamine (30 mg kg(-1) i.p.) nor repeated treatment with amphetamine (1 and 2 mg kg(-1) i.p., daily for 5 days). The enhancing effects of ketamine (30 mg kg(-1) day(-1) i.p.) on the duration of immobility in the FST were attenuated by clozapine (1, 5 and 10 mg kg(-1) i.p.), risperidone (0.25 and 0.5 mg kg(-1) i.p.) and paroxetine (1 and 5 mg kg(-1) i.p.). Haloperidol (0.25 and 0.50 mg kg(-1) day(-1) i.p.) failed to attenuate the ketamine-enhanced immobility in the FST. The repeated ketamine administration neither affects locomotor activity nor motor coordination in rats under the same treatment conditions with the FST, suggesting that the effects of ketamine on the duration of immobility in this study was neither due to motor dysfunction nor peripheral neuromuscular blockade. Our results suggest that repeated treatment with subanaesthetic doses of ketamine enhance the duration of immobility in FST, which might be a useful animal model for the negative symptoms (particularly the depressive features) of schizophrenia.

Acute behavioral effects of nicotine in male and female HINT1 knockout mice

Human genetic association and brain expression studies, and mouse behavioral and molecular studies implicate a role for the histidine triad nucleotide-binding protein 1 (HINT1) in schizophrenia, bipolar disorder, depression and anxiety. The high comorbidity between smoking and psychiatric disorders, schizophrenia in particular, is well established. Associations with schizophrenia and HINT1 are also sex specific, with effects more predominant in males; however, it is unknown if sex differences associated with the gene extend to other phenotypes. Thus, in this study, using a battery of behavioral tests, we elucidated the role of HINT1 in acute nicotine-mediated behaviors using male and female HINT1 wild-type (+/+) and knockout (-/-) mice. The results show that male HINT1 -/- mice were less sensitive to acute nicotine-induced antinociception in the tail-flick, but not hot-plate test. At low nicotine doses, male and female HINT1 -/- mice were less sensitive to nicotine-induced hypomotility, although the effect was more pronounced in females. Baseline differences in locomotor activity observed in male HINT1 +/+ and -/- mice were absent in females. Nicotine did not produce an anxiolytic effect in male HINT1 -/- mice, but rather an anxiogenic response. Diazepam also failed to induce an anxiolytic response in these mice, suggesting a general anxiety phenotype not specific to nicotine. Differences in anxiety-like behavior were not observed in female mice. These results further support a role for HINT1 in nicotine-mediated behaviors and suggest that alterations in the gene may have differential effects on phenotype in males and females.

Plasma total antioxidant status and cognitive impairments in schizophrenia

Oxidative stress-induced damage to neurons may contribute to cognitive deficits during aging and in neurodegenerative disorders. Schizophrenia has a range of cognitive deficits that may evolve from oxidative stress, and this study examines this association of oxidative stress with cognitive deficits in schizophrenia. We recruited 296 chronic schizophrenia patients and 181 healthy control subjects and examined the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and plasma total antioxidant status (TAS) in both groups. Schizophrenia symptoms were assessed using the positive and negative syndrome scale (PANSS). Our results showed that TAS levels were significantly lower in patients than controls (179.6 ± 81.0 U/ml vs. 194.8 ± 46.0 U/ml, p<0.05). Cognitive scores on the RBANS and nearly all of its five subscales (all p<0.001) except for the Visuospatial/Constructional index (p>0.05) were significantly lower in schizophrenia patients than normal controls. For the patients, TAS was inversely associated with some domains of cognitive deficits in schizophrenia, such as Attention and Immediate Memory. Our findings suggest that oxidative stress may be involved in the pathophysiology of schizophrenia, and its associated cognitive impairment.

Characterization of the neuropsychological phenotype of glycine N-methyltransferase-/- mice and evaluation of its responses to clozapine and sarcosine treatments

Glycine N-methyltransferase (GNMT) affects cellular methylation capacity through regulating the ratio between S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH). The product of its enzymatic reaction-sarcosine has antipsychotic effect in patients with schizophrenia. In this study, through RT-PCR and immunohistochemical staining, we demonstrated that GNMT expressed in various neurons located in the cerebral cortex, hippocampus, substantia nigra and cerebellum. Compared to the wild-type mice, Gnmt-/- mice had significantly lower level of sarcosine in the cerebral cortex. Real-time PCR identified genes involved in the methionine metabolism (Dnmt1 and Dnmt3a), ErbB (Nrg1 and ErbB4) and mTOR (Akt2, S6, S6k1 and S6k2) signaling pathways were dysregulated significantly in the cortex of Gnmt-/- mice. Acoustic startle reflex test demonstrated that Gnmt-/- mice had significantly lower level of prepulse inhibition and the deficit was ameliorated through clozapine or sarcosine treatment. Furthermore, liver-specific-human-GNMT transgenic with Gnmt-/- (Tg-GNMT/Gnmt-/-) mice were used to rule out that the phenotype was due to abnormal liver function. In summary, the neuropsychological abnormalities found in Gnmt-/- mice may represent an endophenotype of schizophrenia. GNMT plays an important role in maintaining normal physiological function of brain and Tg-GNMT/Gnmt-/- mice are useful models for development of therapeutics for patients with schizophrenia.

T-817MA, but Not Haloperidol and Risperidone, Restores Parvalbumin-Positive γ -Aminobutyric Acid Neurons in the Prefrontal Cortex and Hippocampus of Rats Transiently Exposed to MK-801 at the Neonatal Period

The number of parvalbumin (PV)-positive γ-aminobutyric acid (GABA) neurons is decreased in the brain of rats transiently exposed to MK-801, an N-methyl-D-aspartate (NMDA) receptor blocker, in the neonatal stage (Uehara et al. (2012)). T-817MA [1-{3-[2-(1-benzothiophen-5-yl)ethoxy]propyl} azetidin-3-ol maleate] is a neuroprotective agent synthesized for the treatment of psychiatric disorders characterized by cognitive disturbances, such as dementia. We herein sought to determine whether T-817MA, haloperidol (HPD), or risperidone (RPD) would ameliorate the decrease in the number of PV-positive GABA neurons in the medial prefrontal cortex (mPFC) and hippocampus of the model animals. Rats were treated with MK-801 (0.2 mg/kg/day) or vehicle on postnatal days (PD) 7–10, and the number of PV-positive neurons in the mPFC and hippocampus were measured on PDs 63. T-817MA (20 mg/kg), HPD (1 mg/kg), or RPD (1 mg/kg) were administered during PDs 49–62. Fourteen-day administration of T-817MA reversed the decrease in the number of PV-positive neurons in the above brain regions of rats given MK-801, whereas HPD and RPD were ineffective. These results indicate that T-817MA provides a novel pharmacologic strategy to enhance cognitive function in patients with schizophrenia.

Finding the needle in the haystack: a review of microarray gene expression research into schizophrenia

BACKGROUND

With an estimated 80% heritability, molecular genetic research into schizophrenia has remained inconclusive. Recent large-scale, genome-wide association studies only identified a small number of susceptibility genes with individually very small effect sizes. However, the variable expression of the phenotype is not well captured in diagnosis-based research as well as when assuming a 'heterogenic risk model' (as apposed to a monogenic or polygenic model). Hence, the expression of susceptibility genes in response to environmental factors in concert with other disease-promoting or protecting genes has increasingly attracted attention.

METHOD

The current review summarises findings of microarray gene expression research with relevance to schizophrenia as they emerged over the past decade.

RESULTS

Most findings from post mortem, peripheral tissues and animal models to date have linked altered gene expression in schizophrenia to presynaptic function, signalling, myelination, neural migration, cellular immune mechanisms, and response to oxidative stress consistent with multiple small effects of many individual genes. However, the majority of results are difficult to interpret due to small sample sizes (i.e. potential type-2 errors), confounding factors (i.e. medication effects) or lack of plausible neurobiological theory.

CONCLUSION

Nevertheless, microarray gene expression research is likely to play an important role in the future when investigating gene/gene and gene/environment interactions by adopting a neurobiologically sound theoretical framework.

Targeting NOX enzymes in the central nervous system: therapeutic opportunities

Among the pathogenic mechanisms underlying central nervous system (CNS) diseases, oxidative stress is almost invariably described. For this reason, numerous attempts have been made to decrease reactive oxygen species (ROS) with the administration of antioxidants as potential therapies for CNS disorders. However, such treatments have always failed in clinical trials. Targeting specific sources of reactive oxygen species in the CNS (e.g. NOX enzymes) represents an alternative promising option. Indeed, NOX enzymes are major generators of ROS, which regulate progression of CNS disorders as diverse as amyotrophic lateral sclerosis, schizophrenia, Alzheimer disease, Parkinson disease, and stroke. On the other hand, in autoimmune demyelinating diseases, ROS generated by NOX enzymes are protective, presumably by dampening the specific immune response. In this review, we discuss the possibility of developing therapeutics targeting NADPH oxidase (NOX) enzymes for the treatment of different CNS pathologies. Specific compounds able to modulate the activation of NOX enzymes, and the consequent production of ROS, could fill the need for disease-modifying drugs for many incurable CNS pathologies.

Is lead exposure in early life an environmental risk factor for Schizophrenia? Neurobiological connections and testable hypotheses

Schizophrenia is a devastating neuropsychiatric disorder of unknown etiology. There is general agreement in the scientific community that schizophrenia is a disorder of neurodevelopmental origin in which both genes and environmental factors come together to produce a schizophrenia phenotype later in life. The challenging questions have been which genes and what environmental factors? Although there is evidence that different chromosome loci and several genes impart susceptibility for schizophrenia; and epidemiological studies point to broad aspects of the environment, only recently there has been an interest in studying gene × environment interactions. Recent evidence of a potential association between prenatal lead (Pb(2+)) exposure and schizophrenia precipitated the search for plausible neurobiological connections. The most promising connection is that in schizophrenia and in developmental Pb(2+) exposure there is strong evidence for hypoactivity of the N-methyl-d-aspartate (NMDA) subtype of excitatory amino acid receptors as an underlying neurobiological mechanism in both conditions. A hypofunction of the NMDA receptor (NMDAR) complex during critical periods of development may alter neurobiological processes that are essential for brain growth and wiring, synaptic plasticity and cognitive and behavioral outcomes associated with schizophrenia. We also describe on-going proof of concept gene-environment interaction studies of early life Pb(2+) exposure in mice expressing the human mutant form of the disrupted in schizophrenia 1 (DISC-1) gene, a gene that is strongly associated with schizophrenia and allied mental disorders.

Deficits in emotional learning and memory in an animal model of schizophrenia

Alterations in N-methyl-D-aspartate (NMDA) receptor function have been linked to numerous behavioral deficits and neurochemical alterations. Recent investigations have begun to explore the role of NMDA receptor function on principally inhibitory neurons and their role in network function. One of the prevailing models of schizophrenia proposes a reduction in NMDA receptor function on inhibitory interneurons and the resulting disinhibition may give rise to aspects of the disorder. Studies using NMDA receptor antagonists such as PCP and ketamine have induced schizophrenia-like behavioral deficits in animal model systems as well as changes in inhibitory circuits. The current study investigated whether the administration of a subanesthetic dose of ketamine (8 mg/kg subcutaneously), that disrupts sensorimotor gating, also produces impairments in a Pavlovian emotional learning and memory task. We utilized both standard delay and trace cued and contextual fear conditioning (CCF) paradigms to examine if ketamine produces differential effects when the task is more difficult and relies on connectivity between specific brain regions. Rats administered ketamine displayed no significant deficits in cued or contextual fear following the delay conditioning protocol. However, ketamine did produce a significant impairment in the more difficult trace conditioning protocol. Analyses of tissue from the hippocampus and amygdala indicated that the administration of ketamine produced an alteration in GABA receptor protein levels differentially depending on the task. These data indicate that 8 mg/kg of ketamine impairs learning in the more difficult emotional classical conditioning task and may be related to altered signaling in GABAergic systems.

T-817MA, a novel neurotrophic agent, ameliorates loss of GABAergic parvalbumin-positive neurons and sensorimotor gating deficits in rats transiently exposed to MK-801 in the neonatal period

T-817MA [1-{3-[2-(1-benzothiophen-5-yl)ethoxy]propyl}azetidin-3-ol maleate] is a newly synthesized neuroprotective agent for the treatment of psychiatric disorders characterized by cognitive disturbances, such as Alzheimer's disease. Cognitive impairment has also been suggested to be a cardinal feature of schizophrenia. We sought to determine whether T-817MA would ameliorate sensorimotor gating deficits and loss of parvalbumin (PV)-positive γ-aminobutyric acid (GABA) neurons in the brain of rats transiently exposed to MK-801, an N-methyl-d-aspartate receptor blocker, in the neonatal stage, as an animal model of schizophrenia. Prepulse inhibition (PPI) was examined in rats treated neonatally with MK-801 (postnatal day; PD 7-10, 0.2 mg/kg/day, s.c.) or vehicle at PD 35 and PD 63. The number of PV-positive GABAergic neurons in the medial prefrontal cortex (mPFC) and the hippocampus was measured after the behavioral assessments. T-817MA (10 or 20 mg/kg) or vehicle was administered for 14 days (on PD 49-62). Administration of T-817MA at 20 mg/kg, but not 10 mg/kg, ameliorated PPI deficits and completely reversed the decrease in the number of PV-positive GABAergic neurons in rats given MK-801. These results indicate that T-817MA may provide a novel therapeutic approach for the treatment of cognitive deficits of schizophrenia.

Dendritic spine pathology in schizophrenia

Schizophrenia is a neurodevelopmental disorder whose clinical features include impairments in perception, cognition and motivation. These impairments reflect alterations in neuronal circuitry within and across multiple brain regions that are due, at least in part, to deficits in dendritic spines, the site of most excitatory synaptic connections. Dendritic spine alterations have been identified in multiple brain regions in schizophrenia, but are best characterized in layer 3 of the neocortex, where pyramidal cell spine density is lower. These spine deficits appear to arise during development, and thus are likely the result of disturbances in the molecular mechanisms that underlie spine formation, pruning, and/or maintenance. Each of these mechanisms may provide insight into novel therapeutic targets for preventing or repairing the alterations in neural circuitry that mediate the debilitating symptoms of schizophrenia.

The challenges and promise of neuroimaging in psychiatry

Neuroimaging is central to the quest for a biological foundation of psychiatric diagnosis but so far has not yielded clinically relevant biomarkers for mental disorders. This review addresses potential reasons for this limitation and discusses refinements of paradigms and analytic techniques that may yield improved diagnostic and prognostic accuracy. Neuroimaging can also be used to probe genetically defined biological pathways underlying mental disorders, for example through the genetic imaging of variants discovered in genome-wide association studies. These approaches may ultimately reveal mechanisms through which genes contribute to psychiatric symptoms and how pharmacological and psychological interventions exert their effects.

Licking and Liking: The Assessment of Hedonic Responses in Rodents

Affective processes are a key determinant of behaviour: At its simplest, liked stimuli are approached while disliked stimuli are avoided. Although assessing hedonic responses in nonverbal animals can be difficult, one relatively tractable approach relies on detailed analyses of rodents' consummatory behaviour. Rodents typically produce rhythmic sets of licks that can be grouped into clusters on the basis of the intervals between licks. The mean number of licks in a cluster (cluster size) is directly related to the concentration of palatable and unpalatable solutions. These relationships suggest that lick cluster size might be a useful index of an animal's hedonic reaction to the solution being consumed. I begin by reviewing studies of conditioned flavour preference and aversion that support the idea that lick cluster size can provide useful information about rats' hedonic reactions. I then describe how this methodology has been used to address previously intractable issues in the investigation of contrast effects as well as revealing an analogue of effort justification effects that, in humans, are commonly explained in terms of cognitive dissonance reduction. Finally, I consider how lick analysis might provide information about hedonic responses in animal models of human psychiatric disorders. In all these cases, how an animal did something was particularly informative about why it was doing it.

Metabotropic glutamate receptors as therapeutic targets for schizophrenia

Treatment options for schizophrenia that address all symptom categories (positive, negative, and cognitive) are lacking in current therapies for this disorder. Compounds targeting the metabotropic glutamate (mGlu) receptors hold promise as a more comprehensive therapeutic alternative to typical and atypical antipsychotics and may avoid the occurrence of extrapyramidal side effects that accompany these treatments. Activation of the group II mGlu receptors (mGlu(2) and mGlu(3)) and the group I mGlu(5) are hypothesized to normalize the disruption of thalamocortical glutamatergic circuitry that results in abnormal glutamaterigic signaling in the prefrontal cortex (PFC). Agonists of mGlu(2) and mGlu(3) have demonstrated efficacy for the positive symptom group in both animal models and clinical trials with mGlu(2) being the subtype most likely responsible for the therapeutic effect. Limitations in the chemical space tolerated by the orthosteric site of the mGlu receptors has led to the pursuit of compounds that potentiate the receptor's response to glutamate by acting at less highly conserved allosteric sites. Several series of selective positive allosteric modulators (PAMs) for mGlu(2) and mGlu(5) have demonstrated efficacy in animal models used for the evaluation of antipsychotic agents. In addition, evidence from animal studies indicates that mGlu(5) PAMs hold promise for the treatment of cognitive deficits that occur in schizophrenia. Hopefully, further optimization of allosteric modulators of mGlu receptors will yield clinical candidates that will allow full evaluation of the potential efficacy of these compounds in the treatment of multiple symptom domains in schizophrenia patients in the near future.