Schizophrenia: from phenomenology to neurobiology

α7 neuronal nicotinic receptor agonist (TC-7020) reverses increased striatal dopamine release during acoustic PPI testing in a transgenic mouse model of schizophrenia

Genetic and post mortem evidence has implicated the α7 neuronal nicotinic receptor (NNR) in the etiology of schizophrenia and related disorders. In schizophrenia, enhanced subcortical dopamine (DA) correlates with positive and cognitive of the disease, including impairments in sensorimotor gating. We measured the levels of extracellular DA and DA metabolites during an acoustic test session of prepulse inhibition (PPI) of the startle response, a measure of sensorimotor gating, by microdialysis and HPLC-EC in a transgenic mouse model of schizophrenia. In th-fgfr1(tk-) mice, blockade of fibroblast growth factor receptor 1 (FGFR1) signaling during development in catecholaminergic neurons results in reduced size and density of midbrain DA neurons of the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA). These mice displayed reduced PPI and enhanced startle response relative to control mice as well as a potentiation of DA release in the dorsal striatum during a 30 minute PPI test session. Acute administration of a partial α7 NNR agonist TC-7020 (1.0 mg/kg) normalized PPI and startle deficits and attenuated increases of DA release during acoustic PPI testing. These results provide direct evidence of elevated striatal dopaminergic transmission with impaired sensorimotor gating that may underlie cognitive and positive symptoms and motor deficits in schizophrenia and related disorders. Also, systemic targeting of alpha7 NNRs may ameliorate these deficits by functionally suppressing striatal DA activity.

ERP investigation of study-test background mismatch during face recognition in schizophrenia

Old/new effects on event-related potentials (ERP) were explored in 20 patients with schizophrenia and 20 paired comparison subjects during unfamiliar face recognition. Extrinsic perceptual changes - which influence the overall familiarity of an item while retaining face-intrinsic features for use in structural face encoding - were manipulated between the study phase and the test. The question raised here concerns whether these perceptual incongruities would have a different effect on the sense of familiarity and the corresponding behavioral and ERP measures in the two groups. The results showed that schizophrenia patients were more inclined to consider old faces shown against a new background as distractors. This drop in face familiarity was accompanied by the disappearance of ERP old/new effects in this condition, i.e., FN400 and parietal old/new effects. Indeed, while ERP old/new recognition effects were found in both groups when the picture of the face was physically identical to the one presented for study, the ERP correlates of recognition disappeared among patients when the background behind the face was different. This difficulty in disregarding a background change suggests that recognition among patients with schizophrenia is based on a global perceptual matching strategy rather than on the extraction of configural information from the face. The correlations observed between FN400 amplitude, the rejection of faces with a different background, and the reality-distortion scores support the idea that the recognition deficit found in schizophrenia results from early anomalies that are carried over onto the parietal ERP old/new effect. Face-extrinsic perceptual variations provide an opportune situation for gaining insight into the social difficulties that patients encounter throughout their lives.

Discovery of potential antipsychotic agents possessing pro-cognitive properties

Current antipsychotic drug therapies for schizophrenia have limited efficacy and are notably ineffective at addressing the cognitive deficits associated with this disorder. The present study was designed to develop effective antipsychotic agents that would also ameliorate the cognitive deficits associated with this disease. In vitro studies comprised of binding and functional assays were utilized to identify compounds with the receptor profile that could provide both antipsychotic and pro-cognitive features. Antipsychotic and cognitive models assessing in vivo activity of these compounds included locomotor activity assays and novel object recognition assays. We developed a series of potential antipsychotic agents with a novel receptor activity profile comprised of muscarinic M(1) receptor agonism in addition to dopamine D(2) antagonism and serotonin 5-HT(2A) inverse agonism. Like other antipsychotic agents, these compounds reverse both amphetamine and dizocilpine-induced hyperactivity in animals. In addition, unlike other antipsychotic drugs, these compounds demonstrate pro-cognitive actions in the novel object recognition assay. The dual attributes of antipsychotic and pro-cognitive actions distinguish these compounds from other antipsychotic drugs and suggest that these compounds are prototype molecules in the development of novel pro-cognitive antipsychotic agents.

Identification of new schizophrenia susceptibility loci in an ethnically homogeneous, family-based, Arab-Israeli sample

While the use of population-based samples is a common strategy in genome-wide association studies (GWASs), family-based samples have considerable advantages, such as robustness against population stratification and false-positive associations, better quality control, and the possibility to check for both linkage and association. In a genome-wide linkage study of schizophrenia in Arab-Israeli families with multiple affected individuals, we previously reported significant evidence for a susceptibility locus at chromosome 6q23.2-q24.1 and suggestive evidence at chromosomes 10q22.3-26.3, 2q36.1-37.3 and 7p21.1-22.3. To identify schizophrenia susceptibility genes, we applied a family-based GWAS strategy in an enlarged, ethnically homogeneous, Arab-Israeli family sample. We performed genome-wide single nucleotide polymorphism (SNP) genotyping and single SNP transmission disequilibrium test association analysis and found genome-wide significant association (best value of P=1.22×10(-11)) for 8 SNPs within or near highly reasonable functional candidate genes for schizophrenia. Of particular interest are a group of SNPs within and flanking the transcriptional factor LRRFIP1 gene. To determine replicability of the significant associations beyond the Arab-Israeli population, we studied the association of the significant SNPs in a German case-control validation sample and found replication of associations near the UGT1 subfamily and EFHD1 genes. Applying an exploratory homozygosity mapping approach as a complementary strategy to identify schizophrenia susceptibility genes in our Arab Israeli sample, we identified 8 putative disease loci. Overall, this GWAS, which emphasizes the important contribution of family based studies, identifies promising candidate genes for schizophrenia.

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

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

Genetic inactivation of GSK3α rescues spine deficits in Disc1-L100P mutant mice

Disrupted-in-Schizophrenia 1 (DISC1), a strong candidate gene for schizophrenia and other mental disorders, regulates neurodevelopmental processes including neurogenesis, neuronal migration, neurite outgrowth and spine development. Glycogen synthase kinase-3 (GSK3) directly interacts with DISC1 and also plays a role in neurodevelopment. Recently, our group showed that the Disc1-L100P mutant protein has reduced interaction with both GSK3α and β. Genetic and pharmacological inhibition of GSK3 activity rescued behavioral abnormalities in Disc1-L100P mutant mice. However, the cellular mechanisms mediating these effects of GSK3 inhibition in Disc1 mutant mice remain unclear. We sought to investigate the effects of genetic inactivation of GSK3α on frontal cortical neuron morphology in Disc1 L100P mutant mice using Golgi staining. We found a significant decrease in dendritic length and surface area in Disc1-L100P, GSK3α null and L100P/GSK3α double mutants. Dendritic spine density was significantly reduced only in Disc1-L100P and L100P/GSK3α +/- mice when compared to wild-type littermates. There was no difference in dendritic arborization between the various genotypes. No significant rescue in dendritic length and surface area was observed in L100P/GSK3α mutants versus L100P mice, but spine density in L100P/GSK3α mice was comparable to wild-type. Neurite outgrowth and spine development abnormalities induced by Disc1 mutation may be partially corrected through GSK3α inactivation, which also normalizes behavior. However, many of the other dendritic abnormalities in the Disc1-L100P mutant mice were not corrected by GSK3α inactivation, suggesting that only some of the anatomical defects have observable behavioral effects. These findings suggest novel treatment approaches for schizophrenia, and identify a histological read-out for testing other therapeutic interventions.

Disc1 point mutations in mice affect development of the cerebral cortex

Disrupted-in-Schizophrenia 1 (DISC1) is a strong candidate gene for schizophrenia and other mental disorders. DISC1 regulates neurodevelopmental processes including neurogenesis, neuronal migration, neurite outgrowth, and neurotransmitter signaling. Abnormal neuronal morphology and cortical architecture are seen in human postmortem brain from patients with schizophrenia. However, the etiology and development of these histological abnormalities remain unclear. We analyzed the histology of two Disc1 mutant mice with point mutations (Q31L and L100P) and found a relative reduction in neuron number, decreased neurogenesis, and altered neuron distribution compared to wild-type littermates. Frontal cortical neurons have shorter dendrites and decreased surface area and spine density. Overall, the histology of Disc1 mutant mouse cortex is reminiscent of the findings in schizophrenia. These results provide further evidence that Disc1 participates in cortical development, including neurogenesis and neuron migration.

Modelling schizophrenia using human induced pluripotent stem cells

Schizophrenia (SCZD) is a debilitating neurological disorder with a world-wide prevalence of 1%; there is a strong genetic component, with an estimated heritability of 80-85%. Although post-mortem studies have revealed reduced brain volume, cell size, spine density and abnormal neural distribution in the prefrontal cortex and hippocampus of SCZD brain tissue and neuropharmacological studies have implicated dopaminergic, glutamatergic and GABAergic activity in SCZD, the cell types affected in SCZD and the molecular mechanisms underlying the disease state remain unclear. To elucidate the cellular and molecular defects of SCZD, we directly reprogrammed fibroblasts from SCZD patients into human induced pluripotent stem cells (hiPSCs) and subsequently differentiated these disorder-specific hiPSCs into neurons (Supplementary Fig. 1). SCZD hiPSC neurons showed diminished neuronal connectivity in conjunction with decreased neurite number, PSD95-protein levels and glutamate receptor expression. Gene expression profiles of SCZD hiPSC neurons identified altered expression of many components of the cyclic AMP and WNT signalling pathways. Key cellular and molecular elements of the SCZD phenotype were ameliorated following treatment of SCZD hiPSC neurons with the antipsychotic loxapine. To date, hiPSC neuronal pathology has only been demonstrated in diseases characterized by both the loss of function of a single gene product and rapid disease progression in early childhood. We now report hiPSC neuronal phenotypes and gene expression changes associated with SCZD, a complex genetic psychiatric disorder.

Nocturnal hyperactivity, increased social novelty preference and delayed extinction of fear responses in post-weaning socially isolated mice

When rodents are reared in isolation from young age onwards, they manifest a number of behavioural alterations in adulthood. Since some of these alterations resemble symptoms of psychiatric disorders, the post-weaning social isolation (ISO) manipulation is often applied to create rodent models of these disorders. In rats, ISO effects have been thoroughly characterised, but in mice they are less well documented. Therefore, we further evaluated behaviour of adult ISO mice with a test battery that focussed on abnormalities relevant to schizophrenia. We found that ISO mice were hyperactive during the dark phase. Also, ISO mice showed alterations in magnitude, habituation and prepulse-inhibition of the acoustic startle reflex, increased anxiety, increased social preference and changes in extinction of fear responses. We did not observe increased sensitivity to locomotor-activating effects of amphetamine. It is concluded that ISO of mice might serve as a useful model to test further hypotheses regarding pathogenesis occurring at specific developmental timeframes.

Metabonomic studies of schizophrenia and psychotropic medications: focus on alterations in CNS energy homeostasis

Schizophrenia is a severe neuropsychiatric disorder with a poorly understood etiology and progression. We and other research groups have found that energy metabolic pathways in the CNS are perturbed in many subjects with this disorder. Antipsychotic drugs that generally target neurotransmission are currently used for clinical management of the disorder, although these can also have marked effects on energy metabolism in the CNS and periphery. Recent proteomic and metabonomic studies have shown that molecular pathways associated with brain energy metabolism are altered in both the disorder and by antipsychotic treatments. This review focuses on discussion of these molecular alterations. Increased knowledge in this area could facilitate biomarker identification and drug discovery based on improving brain energy metabolism in this debilitating disorder.

Prenatal exposure to a viral mimetic alters behavioural flexibility in male, but not female, rats

Current understanding of the etiology of neurodevelopmental disorders is limited; however, recent epidemiological studies demonstrate a strong correlation between prenatal infection during pregnancy and the development of schizophrenia in adult offspring. In particular, schizophrenia patients subjected to prenatal infection exhibit impairments in executive functions greater than schizophrenia patients not exposed to an infection while in utero. Acute prenatal treatment of rodents with the viral mimetic polyinosinic-polycytidylic acid (PolyI:C) induces behavioural and neuropathological alterations in the adult offspring similar to schizophrenia. However, impairments on tasks of executive function that involve the prefrontal cortex (PFC) have been rarely examined for the prenatal infection model. Hence, we investigated the effects of acute prenatal injection of PolyI:C (4.0 mg/kg, i.v., gestational day 15) on strategy set-shifting and reversal learning in an operant-based task. Our results show male, but not female, PolyI:C-treated adult offspring require more trials to reach criterion and perseverate during set-shifting. An opposite pattern was seen on the reversal day where the PolyI:C-treated male rats made fewer regressive errors. Females took more pre-training days and were slower to respond during the trials when compared to males regardless of prenatal treatment. The present findings validate the utility of the prenatal infection model for examining alterations of executive function, one of the most prominent cognitive symptoms of schizophrenia.

QSAR-CoMSIA applied to antipsychotic drugs with their dopamine D2 and serotonine 5HT2A membrane receptors

Antipsychotic drugs are psychiatric medication primarily used to manage psychosis (e.g., delusions or hallucinations), particularly in schizophrenia and bipolar disorder. First and second generations of antipshychotics tend to block receptors in the brain's dopamine pathways, but antipsychotic drugs encompass a wide range of receptor targets. The inhibition constant, Ki, at the level of membrane receptors is a major determinant of their pharmacokinetic behavior and, consequently, it can affect their antipsychotic activity. Here, predicted inhibition constants, Ki for 71 antipsychotics, already approved for clinical treatment, as well as representative new chemical structures which exhibit antipsychotic activity, were evaluated using 3D-QSAR-CoMSIA models. Significant values of the cross-validated correlation q2 (higher than 0.70) and the fitted correlation r2 (higher than 0.80) revealed that these models have reasonable power to predict the biological affinity of the 15 new risperidone and 12 new olanzapine derivatives in interactions with dopamine D2 and serotonin 5HT2A receptors; these compounds are suggested for further studies.

Converging evidence of blood-based biomarkers for schizophrenia: an update

This chapter has carried out a review of the literature and combined this with the results of in-house studies to identify candidate blood-based biomarkers for schizophrenia and antipsychotic drug response. Literature searches retrieved 185 publications describing a total of 273 schizophrenia biomarkers identified in serum and/or plasma. Examination of seven in-house multicenter studies resulted in the identification of 137 serum/plasma biomarkers. Taken together, the findings suggested an ongoing immunological and inflammatory process in schizophrenia. This was accompanied by altered cortisol levels which suggested activated stress response and altered hypothalamic-pituitary-adrenal axis function in these patients. The authors conclude that such biomarkers may prove useful as additional parameters for characterizing specific immune and/or metabolic or hormonal subsystems in schizophrenia and might, therefore, facilitate the development of future patient stratification and personalized medicine strategies.

In vitro findings of alterations in intracellular calcium homeostasis in schizophrenia

The pathogenesis of schizophrenia involves several complex cellular mechanisms and is not well understood. Recent research has demonstrated an association between primary disturbances characteristic of the disease, including altered dopaminergic and glutamatergic neurotransmission, and impairments in neuronal calcium (Ca(2+)) homeostasis and signaling. Emerging Ca(2+) hypothesis links and unifies various cellular processes involved in the pathogenesis of schizophrenia and suggests a central role of dysregulation of Ca(2+) homeostasis in the etiology of the disease. This review explores the in vitro data on Ca(2+) homeostasis and signaling in schizophrenia. Major limitation in this research is the lack of schizophrenia markers and validated disease models. As indicated in this review, one way to overcome these limitations may be analyses of Ca(2+) signalosomes in peripheral cells from schizophrenia patients. Validation of animal models of schizophrenia may permit the application of advanced Ca(2+) imaging techniques in living animals.

Phencyclidine withdrawal disrupts episodic-like memory in rats: reversal by donepezil but not clozapine

Episodic memory is the capacity to recall an event in time and place (What? Where? When?). Impaired episodic memory is a debilitating cognitive symptom in schizophrenia but is poorly controlled by currently available antipsychotic drugs. Consistent with glutamatergic abnormality in schizophrenia, the NDMA receptor antagonist, phencyclidine (PCP), induces persistent 'schizophrenia-like' symptoms including memory deficits in humans and rodents and is widely used as an animal model of the disorder. However, in contrast to humans, PCP and PCP withdrawal-induced memory deficits in rodents are reversed by antipsychotic drugs such as clozapine. One possible explanation is that the memory tasks used in animal studies do not simultaneously test the What? Where? When? components that characterize episodic memory in human tasks. We investigated whether subchronic PCP withdrawal disrupts memory in rats in a task that requires simultaneous integration of memory for object, place and context. Rats learn to discriminate objects under specific spatial and contextual conditions analogous to the What? Where? When? components of human episodic memory. We found that PCP withdrawal impaired performance on this task and that the atypical antipsychotic drug clozapine did not reverse this impairment. However the acetylcholinesterase inhibitor (AChEI) donepezil, which has been shown to improve episodic memory in humans did reverse the effect of PCP. This suggests that PCP withdrawal disruption of object-place-context recognition in rats may prove to be a useful model to investigate episodic memory impairment in schizophrenia and supports the suggestion that AChEIs could prove to be a useful pharmacological strategy to specifically treat episodic memory problems in schizophrenia.

Complexin2 null mutation requires a 'second hit' for induction of phenotypic changes relevant to schizophrenia

Schizophrenia is a devastating disease that affects approximately 1% of the population across cultures. Its neurobiological underpinnings are still unknown. Accordingly, animal models of schizophrenia often lack construct validity. As concordance rate in monozygotic twins amounts to only 50%, environmental risk factors (e.g. neurotrauma, drug abuse, psychotrauma) likely act as necessary 'second hit' to trigger/drive the disease process in a genetically predisposed individual. Valid animal models would have to consider this genetic-environmental interaction. Based on this concept, we designed an experimental approach for modeling a schizophrenia-like phenotype in mice. As dysfunction in synaptic transmission plays a key role in schizophrenia, and complexin2 (CPLX2) gene expression is reduced in hippocampus of schizophrenic patients, we developed a mouse model with Cplx2 null mutation as genetic risk factor and a mild parietal neurotrauma, applied during puberty, as environmental 'second hit'. Several months after lesion, Cplx2 null mutants showed reduced pre-pulse inhibition, deficit of spatial learning and loss of inhibition after MK-801 challenge. These abnormalities were largely absent in lesioned wild-type mice and non-lesioned Cplx2 null mutants. Forced alternation in T-maze, object recognition, social interaction and elevated plus maze tests were unaltered in all groups. The previously reported mild motor phenotype of Cplx2 null mutants was accentuated upon lesion. MRI volumetrical analysis showed a decrease of hippocampal volume exclusively in lesioned Cplx2 null mutants. These findings provide suggestive evidence for the 'second hit' hypothesis of schizophrenia and may offer new tools for the development of advanced treatment strategies.

Further neurochemical and behavioural investigation of Brattleboro rats as a putative model of schizophrenia

Brattleboro (BRAT) rats are a mutant variant of the Long-Evans (LE) strain deficient in the neurohormone vasopressin. BRAT rats show behavioural alterations relevant to schizophrenia. In particular, BRAT rats show deficits in prepulse inhibition (PPI) and alterations in various measures of cognition. The aim of this study was to replicate the reported PPI deficits in BRAT rats and its reversal by antipsychotic drugs and to investigate other behavioural and neurochemical characteristics. Acoustic startle reactivity, PPI, spontaneous and amphetamine-induced locomotor activity (LMA) and ex-vivo steady state neurochemistry were measured in male homozygous BRAT rats and LE rats. The effects of antipsychotics on PPI deficits were also determined. Relative to LE, BRAT rats showed enhanced startle reactivity, hyperactivity to a novel environment, PPI deficits and decreased levels of dopamine and DOPAC (dihydroxyphenylacetic acid) in the frontal cortex. BRAT and LE rats showed similar levels of hyperactivity following amphetamine (0.26 mg/kg s.c.). PPI deficits were attenuated by acute clozapine (5-10 mg/kg s.c.), risperidone (0.1-1 mg/kg i.p.), haloperidol (0.1-0.5 mg/kg p.o.) and less robustly by olanzapine (0.3-3 mg/kg s.c.). Chronic administration of clozapine (5 mg/kg s.c., once daily) attenuated baseline hyperactivity and elevated PPI of both strains. Clozapine concentrations were higher in BRAT brains compared with LE rats. These data confirm the reported PPI deficit in BRAT rats and its reversal by antipsychotic drugs, suggesting BRAT rats may represent a potential model for identifying novel antipsychotic drugs.

Analyzing the effects of psychotropic drugs on metabolite profiles in rat brain using 1H NMR spectroscopy

The mechanism of action of standard drug treatments for psychiatric disorders remains fundamentally unknown, despite intensive investigation in academia and the pharmaceutical industry. So far, little is known about the effects of psychotropic medications on brain metabolism in either humans or animals. In this study, we investigated the effects of a range of psychotropic drugs on rat brain metabolites. The drugs investigated were haloperidol, clozapine, olanzapine, risperidone, aripiprazole (antipsychotics); valproate, carbamazapine (mood stabilizers) and phenytoin (antiepileptic drug). The relative concentrations of endogenous metabolites were determined using high-resolution proton nuclear magnetic resonance (1H NMR) spectroscopy. The results revealed that different classes of psychotropic drugs modulated a range of metabolites, where each drug induced a distinct neurometabolic profile. Some common responses across several drugs or within a class of drug were also observed. Antipsychotic drugs and mood stabilizers, with the exception of olanzapine, consistently increased N-acetylaspartate (NAA) levels in at least one brain area, suggesting a common therapeutic response on increased neuronal viability. Most drugs also altered the levels of several metabolites associated with glucose metabolism, neurotransmission (including glutamate and aspartate) and inositols. The heterogenic pharmacological response reflects the functional and physiological diversity of the therapeutic interventions, including side effects. Further study of these metabolites in preclinical models should facilitate the development of novel drug treatments for psychiatric disorders with improved efficacy and side effect profiles.

Syntheses of two potential dopamine D4 receptor radioligands: 18F labelled chromeno[3,4-c]pyridin-5-ones

The dopamine D4 receptor is hypothesized to relate with the pathophysiology and pharmacotherapy of schizophrenia while its level in brain regions is much lower and to date no suitable tracer is available for the study of D4 receptor in vivo . Therefore, selective imaging agents for the D4 subtype are badly needed. Based on the structure-activity analysis of chromeno[3,4-c]pyridin-5-ones as dopamine D4 receptor ligands, two fluorine-18 labelled chromeno[3,4-c] pyridin-5-one derivatives, 3-(4-[18F]fluorobenzyl)-8-hydroxy-1,2,3,4-tetrahydrochromeno[3,4-c]pyridin-5-one and 3-(4-[18F]fluorobenzyl)-8,9-dimethoxy-1,2,3,4-tetrahydrochromeno[3,4-c]pyridin-5-one were synthesized through a two-step one-pot method. Their radiochemical yields were around 19.7% (decay-corrected) and radiochemical purities were higher than 95% with specific activities of about 120 GBq/μmol.

Entorhinal cortex and cognition

Understanding the function of the entorhinal cortex (EC) has been an important subject over the years, not least because of its cortical intermediary to and from the hippocampus proper, and because of electrophysiological advances which have started to reveal the physiology in behaving animals. Clearly, a lot more needs to be done but is clear to date that EC is not merely a throughput station providing all hippocampal subfields with sensory information, but that processing within EC contributes significantly to attention, conditioning, event and spatial cognition possibly by compressing representations that overlap in time. These are transmitted to the hippocampus, where they are differentiated again and returned to EC. Preliminary evidence for such a role, but also their possible pitfalls are summarised.

Schizophrenia: genetics, prevention and rehabilitation

OBJECTIVE

Genetic factors are largely implicated in predisposing to schizophrenia. Environmental factors contribute to the onset of the disorder in individuals at increased genetic risk. Cognitive deficits have emerged as endophenotypes and potential therapeutic targets for schizophrenia because of their association with functional outcome. The aims of this review were to analyse the joint effect of genetic and environmental (G×E) factors on liability to schizophrenia and to investigate relationships between genes and cognitive endophenotypes focusing on practical applications for prevention and rehabilitation.

METHODS

Medline search of relevant studies published between 1990 and 2008.

RESULTS

In schizophrenia, examples of G×E interaction include the catechol-O-methyl transferase (COMT) (Val158Met) polymorphism, which was found to moderate the onset of psychotic manifestations in response to stress and to increase the risk for psychosis related to cannabis use, and neurodevelopmental genes such as AKT1 (serine-threonine kinase), brain-derived neurotrophic factor (BDNF), DTNBP1 (dysbindin) and GRM3 (metabotropic glutamate receptor 3), which were associated with development of schizophrenia in adulthood after exposure to perinatal obstetric complications. Neurocognitive deficits are recognised as core features of schizophrenia that facilitate the onset of the disorder and have a great impact on functional outcome. Neurocognitive deficits are also endophenotypes that have been linked to a variety of genes [COMT, neuregulin (NRG1), BDNF, Disrupted-In-Schizophrenia 1 (DISC1) and dysbindin] conferring susceptibility to schizophrenia. Recently, it has emerged that cognitive improvement during rehabilitation therapy was under control of COMT (Val158Met) polymorphism.

CONCLUSION

This review could indicate a pivotal role of psychiatric genetics in prevention and rehabilitation of schizophrenic psychoses.

TC-5619: an alpha7 neuronal nicotinic receptor-selective agonist that demonstrates efficacy in animal models of the positive and negative symptoms and cognitive dysfunction of schizophrenia

A growing body of evidence suggests that the alpha7 neuronal nicotinic receptor (NNR) subtype is an important target for the development of novel therapies to treat schizophrenia, offering the possibility to address not only the positive but also the cognitive and negative symptoms associated with the disease. In order to probe the relationship of alpha7 function to relevant behavioral correlates we employed TC-5619, a novel selective agonist for the alpha7 NNR subtype. TC-5619 binds with very high affinity to the alpha7 subtype and is a potent full agonist. TC-5619 has little or no activity at other nicotinic receptors, including the alpha4beta2, ganglionic (alpha3beta4) and muscle subtypes. The transgenic th(tk-)/th(tk-) mouse model that reflects many of the developmental, anatomical, and multi-transmitter biochemical aspects of schizophrenia was used to assess the antipsychotic effects of TC-5619. In these mice TC-5619 acted both alone and synergistically with the antipsychotic clozapine to correct impaired pre-pulse inhibition (PPI) and social behavior which model positive and negative symptoms, respectively. Antipsychotic and cognitive effects of TC-5619 were also assessed in rats. Similar to the results in the transgenic mice, TC-5619 significantly reversed apomorphine-induced PPI deficits. In a novel object recognition paradigm in rats TC-5619 demonstrated long-lasting enhancement of memory over a wide dose range. These results suggest that alpha7-selective agonists such as TC-5619, either alone or in combination with antipsychotics, could offer a new approach to treating the constellation of symptoms associated with schizophrenia, including cognitive dysfunction.

Neuroprotective effect of atypical antipsychotics in cognitive and non-cognitive behavioral impairment in animal models

Antipsychotic drugs are divided into two groups: typical and atypical. Recent clinical studies show atypical antipsychotics have advantages over typical antipsychotics in a wide variety of neuropsychiatric conditions, in terms of greater efficacy for positive and negative symptoms, beneficial effects on cognitive functioning, and fewer extra pyramidal side effects in treating schizophrenia. As such, atypical antipsychotics may be effective in the treatment of depressive symptoms associated with psychotic and mood disorders, posttraumatic stress disorder and psychosis in Alzheimer disease. In this paper, we describe the effects and potential neurochemical mechanisms of action of atypical antipsychotics in several animal models showing memory impairments and/or non-cognitive behavioral changes. The data provide new insights into the mechanisms of action of atypical antipsychotics that may broaden their clinical applications.

Investigation of the expression of genes affecting cytomatrix active zone function in the amygdala in schizophrenia: effects of antipsychotic drugs

The cytomatrix active zone (CAZ) is a specialized cellular structure regulating release of vesicles. We reported previously increased expression of three CAZ genes, piccolo, RIMS2 and RIMS3 in the amygdala in schizophrenia. This study determined the levels of gene and protein expression for components of the active zone including two additional CAZ genes in the amygdala from subjects with schizophrenia and non-psychiatric controls, as well as the effects of antipsychotic drugs. Whilst relative real-time PCR analysis did not identify significant change in the expression of six additional active zone genes, Western blot analysis showed increased piccolo and RIMS2 protein expression in the amygdala in schizophrenia. In vitro analysis suggests antipsychotic drug treatment was unlikely to have caused the changes in RIMS2, RIMS3 and piccolo expression observed in the amygdala in schizophrenia. Therefore, this study provides further evidence suggesting that piccolo, RIMS2, RIMS3, but not the entire components of the active zone are involved in the neurobiology of schizophrenia.

Reduced prefrontal cortex DARPP-32 mRNA in completed suicide victims with schizophrenia

Dopamine-and-cAMP-regulated neuronal phosphoprotein (32 kDa) (DARPP-32), encoded by PPP1R1B, is expressed in brain regions receiving dopaminergic projections, including the prefrontal cortex (PFC), and is implicated in the pathophysiology of schizophrenia. The broad functional capacity of DARPP-32 has potential relevance to both psychotic and negative symptoms of schizophrenia. We wished to determine if DARPP-32 gene expression and variation at selected SNPs correlated significantly with patient phenotypes. We performed RT-PCR to quantify DARPP-32 mRNA from brain samples (Brodmann Area 46) donated by the Stanley Medical Research Institute (SMRI, Array Collection): 35 from unaffected controls (UC), 35 from patients with schizophrenia (SCZ), and 35 with bipolar disorder (BP). Relative mRNA expression was calculated in relation to the housekeeping gene Cyclophilin. SNP genotyping was conducted by PCR on DNA obtained from Brodmann Area 46. We found a significant difference in gene expression levels between SCZ patients who died by suicide (SCZ-S) (n=6) vs. other causes of death (SCZ-NS) (P<0.004), as well as between SCZ-S and UC (P<0.04). We genotyped the intron SNP rs907094 and found that the SCZ-S group was more similar to UC than to the SCZ-NS population. DARPP-32 expression differences between SCZ-S, SCZ-NS, and UC populations are consistent with previous literature suggesting that serotonin system components are also altered in suicide. Work in a larger sample is needed to confirm these findings.

Deletion of the STOP gene, a microtubule stabilizing factor, leads only to discrete cerebral metabolic changes in mice

In mice, deletion of the STOP protein leads to subtle anatomic changes and induces depleted synaptic vesicle pools, impaired synaptic plasticity, hyperdopaminergy, and major behavioral disorders alleviated by neuroleptics, hence leading to a schizophrenic-like phenotype. In this study, we applied the quantitative autoradiographic [(14)C]2-deoxyglucose technique to study to what extent the basal rate of cerebral glucose utilization in STOP-knockout (STOP-KO) mice occurs in regions where metabolic changes have been reported in schizophrenic patients. Studies were performed on wild-type, heterozygous, and homozygous STOP-KO mice (7-8 per group). Mice were implanted with femoral artery and vein catheters, and cerebral glucose utilization was quantified over 45 min. Compared with that in wild-type mice, glucose utilization in STOP-KO mice was significantly increased in the olfactory cortex, ventromedial and anterolateral hypothalamus, ventral tegmental area, and substantia nigra pars compacta. Nonsignificant increases, ranging between 9% and 19%, were recorded in the whole auditory system, CA1 pyramidal cell layer, and dorsal raphe. Glucose utilization was also significantly increased in heterozygous mice compared with that in wild-type mice in olfactory cortex. These data might reflect hyperdopaminergic activity, olfactory deficits, and sleep disturbances in STOP-KO mice that have also been reported in schizophrenic patients.

Nonviral gene transfection nanoparticles: function and applications in the brain

In vivo transfer and expression of foreign genes allows for the elucidation of functions of genes in living organisms and generation of disease models in animals that more closely resemble the etiology of human diseases. Gene therapy holds promise for the cure of a number of diseases at the fundamental level. Synthetic "nonviral" materials are fast gaining popularity as safe and efficient vectors for delivering genes to target organs. Not only can nanoparticles function as efficient gene carriers, they also can simultaneously carry diagnostic probes for direct "real-time" visualization of gene transfer and downstream processes. This review has focused on the central nervous system (CNS) as the target for nonviral gene transfer, with special emphasis on organically modified silica (ORMOSIL) nanoparticles developed in our laboratory. These nanoparticles have shown robust gene transfer efficiency in brain cells in vivo and allowed to investigate mechanisms that control neurogenesis as well as neurodegenerative disorders.

Association of schizophrenia with DTNBP1 but not with DAO, DAOA, NRG1 and RGS4 nor their genetic interaction

Recent reports indicate that DAO, DAOA, DTNBP1, NRG1 and RGS4 are some of the most-replicated genes implicated in susceptibility to schizophrenia. Also, the functions of these genes could converge in a common pathway of glutamate metabolism. The aim of this study was to evaluate if each of these genes, or their interaction, was associated with schizophrenia. A case-control study was conducted in 589 Spanish patients having a diagnosis of schizophrenia, and compared with 617 equivalent control subjects. Several single nucleotide polymorphisms (SNPs) in each gene were determined in all individuals. SNP and haplotype frequencies were compared between cases and controls. The interaction between different SNPs at the same, or at different gene, loci was analyzed by the multifactor dimensionality reduction (MDR) method. We found a new schizophrenia risk and protective haplotypes in intron VII of DTNBP1; one of the most important candidate genes for this disorder, to-date. However, no association was found between DAO, DAOA, NRG1 and RGS4 and schizophrenia. The hypothesis that gene-gene interaction in these five genes could increase the risk for the disorder was not confirmed in the present study. In summary, these results may provide further support for an association between the dysbindin gene (DTNBP1) and schizophrenia, but not between the disease and DAO, DAOA, NRG1 and RGS4 or with the interaction of these genes. In the light of recent data, these results need to be interpreted with caution and future analyses with dense genetic maps are awaited.

Inducible expression of mutant human DISC1 in mice is associated with brain and behavioral abnormalities reminiscent of schizophrenia

A strong candidate gene for schizophrenia and major mental disorders, disrupted-in-schizophrenia 1 (DISC1) was first described in a large Scottish family in which a balanced chromosomal translocation segregates with schizophrenia and other psychiatric illnesses. The translocation mutation may result in loss of DISC1 function via haploinsufficiency or dominant-negative effects of a predicted mutant DISC1 truncated protein product. DISC1 has been implicated in neurodevelopment, including maturation of the cerebral cortex. To evaluate the neuronal and behavioral effects of mutant DISC1, the Tet-off system under the regulation of the CAMKII promoter was used to generate transgenic mice with inducible expression of mutant human DISC1 (hDISC1) limited to forebrain regions, including cerebral cortex, hippocampus and striatum. Expression of mutant hDISC1 was not associated with gross neurodevelopmental abnormalities, but led to a mild enlargement of the lateral ventricles and attenuation of neurite outgrowth in primary cortical neurons. These morphological changes were associated with decreased protein levels of endogenous mouse DISC1, LIS1 and SNAP-25. Compared to their sex-matched littermate controls, mutant hDISC1 transgenic male mice exhibited spontaneous hyperactivity in the open field and alterations in social interaction, and transgenic female mice showed deficient spatial memory. The results show that the neuronal and behavioral effects of mutant hDISC1 are consistent with a dominant-negative mechanism, and are similar to some features of schizophrenia. The present mouse model may facilitate the study of aspects of the pathogenesis of schizophrenia.

Recent progress in the research field of neuropharmacology in China

In recent years, Chinese neuropharmacologists have done a lot of basic and practical work in neuropharmacology, especially in the fields of pain, drug dependence, depression, Alzheimer's disease, schizophrenia, having obtained some exciting results that are of great significance for the development of neuropharmacology. Here I would like to review recent progress in the research fields of neuropharmacology in China.

Altered motor activity, exploration and anxiety in heterozygous neuregulin 1 mutant mice: implications for understanding schizophrenia

Human genetic studies have shown that neuregulin 1 (NRG1) is a potential susceptibility gene for schizophrenia. Nrg1 influences various neurodevelopmental processes, which are potentially related to schizophrenia. The neurodevelopmental theory of schizophrenia suggests that interactions between genetic and environmental factors are responsible for biochemical alterations leading to schizophrenia. To investigate these interactions and to match experimental design with the pathophysiology of schizophrenia, we applied a comprehensive behavioural phenotyping strategy for motor activity, exploration and anxiety in a heterozygous Nrg1 transmembrane domain mutant mouse model (Nrg1 HET) using different housing conditions and age groups. We observed a locomotion- and exploration-related hyperactive phenotype in Nrg1 HETs. Increased age had a locomotion- and exploration-inhibiting effect, which was significantly attenuated in mutant mice. Environmental enrichment (EE) had a stimulating influence on locomotion and exploration. The impact of EE was more pronounced in Nrg1 hypomorphs. Our study also showed a moderate task-specific anxiolytic-like phenotype for Nrg1 HETs, which was influenced by external factors. The behavioural phenotype detected in heterozygous Nrg1 mutant mice is not specific to schizophrenia per se, but the increased sensitivity of mutant mice to exogenous factors is consistent with the pathophysiology of schizophrenia and the neurodevelopmental theory. Our findings reinforce the importance of carefully controlling experimental designs for external factors and of comprehensive, integrative phenotyping strategies. Thus, Nrg1 HETs may, in combination with other genetic and drug models, help to clarify pathophysiological mechanisms behind schizophrenia.

Emotion recognition and genetic vulnerability to schizophrenia

BACKGROUND

Epidemiological studies of schizophrenia suggest that this disorder has a substantial genetic component. Cognitive and social abilities, as well as the volumes of brain regions involved in emotion processing, have been found to be distributed along a continuum when comparing patients, siblings and controls, with siblings showing intermediate scores.

AIMS

To establish whether facial expression recognition is impaired in unaffected siblings of patients.

METHOD

Emotion and gender recognition were evaluated in a three-group pre-post study design in drug-naive patients with first-episode schizophrenia (n=40) and their unaffected siblings (n=30) compared with controls (n=26).

RESULTS

Patients and their healthy siblings showed impaired emotion recognition but normal gender recognition compared with controls. Patients'performance did not improve despite effective clinical stabilisation.

CONCLUSIONS

Impaired performance in healthy siblings and time stability in patients provides evidence of impairment of facial emotion recognition as an actual phenotype of schizophrenia.

Neonatal functional blockade of the entorhinal cortex results in disruption of accumbal dopaminergic responses observed in latent inhibition paradigm in adult rats

Latent inhibition (LI) has been found to be disrupted in non-treated patients with schizophrenia. Dopaminergic (DAergic) dysfunctioning is generally acknowledged to occur in schizophrenia. Various abnormalities in the entorhinal cortex (ENT) have been described in patients with schizophrenia. Numerous data also suggest that schizophrenia has a neurodevelopmental origin. The present study was designed to test the hypothesis that reversible inactivation of the ENT during neonatal development results in disrupted DA responses characteristic of LI in adult rats. Tetrodotoxin (TTX) was microinjected locally in the left ENT at postnatal day 8 (PND8). DA variations were recorded in the dorsomedial shell and core parts of the nucleus accumbens (Nacc) using in vivo voltammetry in freely-moving grown-up rats in a LI paradigm. In the first session the animals were pre-exposed (PE) to the conditional stimulus (banana odour) alone. In the second they were aversively conditioned to banana odour. In the third (test) session the following results were obtained in PE animals subjected to temporary inactivation of the ENT at PND8: (1) aversive behaviour was observed in TTX-PE conditioned animals; (2) DA variations in the dorsomedial shell and core parts of the Nacc were similar in TTX-PE and non-pre-exposed conditioned rats. These findings strongly suggest that neonatal disconnection of the ENT disrupts LI in adult animals. They may further our understanding of the pathophysiology of schizophrenia.

Parent-of-origin effect and genomic imprinting of the HTR2A receptor gene T102C polymorphism in psychosis

Evidence that HTR2A receptor gene may be subject to genomic imprinting prompted us to examine a collection of family trios for evidence of an association between the HTR2A T102C polymorphism and psychosis in schizophrenia or bipolar disorder. We also tested for the possibility of imprinting by employing quantitative RT-PCR to measure the relative expression of post-mortem brain mRNA for each allele in 45 subjects who were heterozygous for the T102C polymorphism. We found that the ratio of C102 to 102T allele mRNA expression was the same in major psychoses and healthy controls. There was no genetic association between HTR2A T102C with either schizophrenia or bipolar disorder under the assumption of a parent-of-origin effect, and these data together essentially exclude imprinting at this locus as a potential explanation for the complex inheritance observed in major psychoses.

Heterozygous neuregulin 1 mice are more sensitive to the behavioural effects of Delta9-tetrahydrocannabinol

RATIONALE

Cannabis use may precipitate schizophrenia especially if the individual has a genetic vulnerability to this mental disorder. Human and animal research indicates that neuregulin 1 (Nrg1) is a susceptibility gene for schizophrenia.

OBJECTIVES

The aim of this study was to investigate whether dysfunction in the Nrg1 gene modulates the behavioural effects of Delta(9)-tetrahydrocannabinol (THC), the major psychotropic component of cannabis.

MATERIALS AND METHODS

Heterozygous Nrg1 transmembrane-domain knockout mice (Nrg1 HET) were treated with acute THC (0, 5 or 10 mg/kg i.p.) 30 min before being tested using open field (OF), hole board (HB), light-dark (LD), elevated plus maze (EPM), social interaction (SI) and prepulse inhibition (PPI) tests.

RESULTS

Nrg1 HET mice showed differences in baseline behaviour with regard to locomotor activity, exploration and anxiety. More importantly, they were more sensitive to the locomotor suppressant actions of THC compared to wild type-like (WT) mice. In addition, Nrg1 HET mice expressed a greater THC-induced enhancement in % PPI than WT mice. The effects of THC on anxiety-related behaviour were task-dependent, with Nrg1 HET mice being more susceptible than WT mice to the anxiogenic effects of THC in LD, but not in the EPM, SI and OF tests.

CONCLUSIONS

Nrg1 HET mice were more sensitive to the acute effects of THC in an array of different behaviours including those that model symptoms of schizophrenia. It appears that variation in the schizophrenia-related neuregulin 1 gene alters the sensitivity to the behavioural effects of cannabinoids.

Antipsychotic profile of rolipram: efficacy in rats and reduced sensitivity in mice deficient in the phosphodiesterase-4B (PDE4B) enzyme

RATIONALE

Recent studies provide evidence for reduced phosphodiesterase-4B (PDE4B) as a genetic susceptibility factor as well as suggesting an association of several single nucleotide polymorphisms (SNPs) in PDE4B that are associated with an increased incidence of schizophrenia.

OBJECTIVES

The aim of the current study was to assess the activity of rolipram, a nonsubtype-selective PDE4 inhibitor, in several animal models predictive of antipsychotic-like efficacy and side-effect liability and to use PDE4B wild-type and knockout mice to begin to understand the subtypes involved in the activity of rolipram.

RESULTS

In rats, rolipram antagonized both phencyclidine hydrochloride- and D-amphetamine-induced hyperactivity and inhibited conditioned avoidance responding (CAR). In PDE4B wild-type mice, rolipram dose-dependently suppressed CAR (ED(50) = 2.4 mg/kg); however, in knockout mice, their sensitivity to rolipram at the higher doses (1.0 and 3.2 mg/kg) was reduced, resulting in a threefold shift in the ED(50) (7.3 mg/kg), suggesting PDE4B is involved, at least in part, with the activity of rolipram. Only the highest dose of rolipram (3.2 mg/kg) produced a modest but significant degree of catalepsy.

CONCLUSIONS

Rolipram has a pharmacologic profile similar to that of the atypical antipsychotics and has low extrapyramidal symptom liability. These results suggest that PDE4B mediates the antipsychotic effects of rolipram in CAR and that the PDE4B-regulated cyclic adenosine monophosphate signaling pathway may play a role in the pathophysiology and pharmacotherapy of psychosis.

Synthesis and in vitro binding studies of substituted piperidine naphthamides. Part II: Influence of the substitution on the benzyl moiety on the affinity for D2L, D4.2, and 5-HT2A receptors

In continuation of our work on N-(piperidin-4-yl)-naphthamides, the effect of substituted benzyl groups on D(2L), D(4.2), and 5-HT(2A) receptor affinity was evaluated. In the 1-naphthamide series most compounds were highly selective for D(4.2) over D(2L) and 5-HT(2A) receptors. Halogen and methyl substitution in position 3 or 4 of the benzyl group increased D(4.2) affinity. In the 2-naphthamide series a similar high D(4.2) over D(2L) selectivity was retained while 5-HT(2A) affinity was increased. 3-Methoxy, 3-methyl, and 4-methyl substituents were favorable for D(4.2) affinity while halogens reduced affinity. 2-Naphthamides with a 3-bromo- or a 3-methyl group were mixed D(4.2)/5-HT(2A) ligands similar to their unsubstituted parent compound. All compounds from both series with significant affinity for D(4.2) and 5-HT(2A) receptors were antagonists.