Sensory gating and alpha-7 nicotinic receptor gene allelic variants in schizoaffective disorder, bipolar type

Early and middle latency auditory event-related potentials do not explain differences in neuropsychological performance between schizophrenia spectrum patients and matched healthy controls

Abnormalities of early and middle latency auditory event-related potentials (ERPs) are widespread in schizophrenia and have been suggested to be associated with cognitive deficits in schizophrenia patients. In this cross-sectional study with schizophrenia patients (n=30) and psychiatrically healthy counterparts (n=31) (matched for age, sex, education), we investigated whether auditory information processing (measured via amplitudes and gating of the auditory ERPs P50, N100 and P200) correlates with neuropsychological performance across cognitive domains. The groups differed significantly in amplitudes and gating of N100 and P200 potentials as well as in neuropsychological performance, but not in P50 amplitude and gating. Neither amplitudes nor gating of auditory ERPs correlated with neuropsychological performance. Neuropsychological intergroup differences could not be explained by abnormalities in auditory information processing. Although pronounced impairments exist on the levels of both auditory information processing and cognitive performance in schizophrenia, these abnormalities are not directly associated with each other.

Brain Network Analysis of EEG Recordings Can Be Used to Assess Cognitive Function in Teenagers With 15q13.3 Microdeletion Syndrome

15q13.3 microdeletion syndrome causes a spectrum of cognitive disorders, including intellectual disability and autism. We assessed the ability of the EEG analysis algorithm Brain Network Analysis (BNA) to measure cognitive function in 15q13.3 deletion patients, and to differentiate between patient and control groups. EEG data was collected from 10 individuals with 15q13.3 microdeletion syndrome (14–18 years of age), as well as 30 age-matched healthy controls, as the subjects responded to Auditory Oddball (AOB) and Go/NoGo cognitive tasks. It was determined that BNA can be used to evaluate cognitive function in 15q13.3 microdeletion patients. This analysis also significantly differentiates between patient and control groups using 5 scores, all of which are produced from ERP peaks related to late cortical components that represent higher cognitive functions of attention allocation and response inhibition (P < 0.05).

Meta-analysis of auditory P50 sensory gating in schizophrenia and bipolar disorder

The ability of the brain to reduce the amount of trivial or redundant sensory inputs is called gating function. Dysfunction of sensory gating may lead to cognitive fragmentation and poor real-world functioning. The auditory dual-click paradigm is a pertinent neurophysiological measure of sensory gating function. This meta-analysis aimed to examine the subcomponents of abnormal P50 waveforms in bipolar disorder and schizophrenia to assess P50 sensory gating deficits and examine effects of diagnoses, illness states (first-episode psychosis vs. schizophrenia, remission vs. episodes in bipolar disorder), and treatment status (medication-free vs. medicated). Literature search of PubMed between Jan 1st 1980 and March 31st 2019 identified 2091 records for schizophrenia, 362 for bipolar disorder. 115 studies in schizophrenia (4932 patients), 16 in bipolar disorder (975 patients) and 10 in first-degree relatives (848 subjects) met the inclusion criteria. P50 sensory gating ratio (S2/S1) and S1-S2 difference were significantly altered in schizophrenia, bipolar disorder and their first-degree relatives. First-episode psychosis did not differ from schizophrenia, however episodes altered P50 sensory gating in bipolar disorder. Medications improve P50 sensory gating alterations in schizophrenia significantly and at trend level in bipolar disorder. Future studies should examine longitudinal course of P50 sensory gating in schizophrenia and bipolar disorder.

The wonderland of neuronal nicotinic acetylcholine receptors

Nearly 30 years of experimental evidence supports the argument that ligands of nicotinic acetylcholine receptors (nAChRs) have potential as therapeutic agents. However, as in the famous Lewis Carroll novel "Alice in Wonderland", there have been many unexpected adventures along the pathway of development, and few nAChR ligands have been approved for any clinical condition to date with the exception of nicotine dependence. The recent failures of nAChR ligands in AD and schizophrenia clinical trials have reduced enthusiasm for this therapeutic strategy and many pharmaceutical companies have now abandoned this field of research. As with other clinical failures, multiple questions arise as to the basis for the failure. More generic questions focus on a potential translational gap between the animal models used and the human clinical condition they are meant to simulate, or the clinical trial mindset that large Ns have to be achieved for statistical power (often requiring multiple trial sites) as opposed to smaller patient cohorts at limited sites where conditions can be better controlled and replicated. More specific to the nAChR field are questions about subtype selectivity, dose selection, whether an agonist, antagonist, or allosteric modulator strategy is best, etc. The purpose of this review is to discuss each of these questions, but also to provide a brief overview of the remarkable progress that has been made over the last three decades in our understanding of this unique ligand-gated ion channel and how this new knowledge may help us improve drug development successes in the future.

The human CHRNA7 and CHRFAM7A genes: A review of the genetics, regulation, and function

The human α7 neuronal nicotinic acetylcholine receptor gene (CHRNA7) is ubiquitously expressed in both the central nervous system and in the periphery. CHRNA7 is genetically linked to multiple disorders with cognitive deficits, including schizophrenia, bipolar disorder, ADHD, epilepsy, Alzheimer's disease, and Rett syndrome. The regulation of CHRNA7 is complex; more than a dozen mechanisms are known, one of which is a partial duplication of the parent gene. Exons 5-10 of CHRNA7 on chromosome 15 were duplicated and inserted 1.6 Mb upstream of CHRNA7, interrupting an earlier partial duplication of two other genes. The chimeric CHRFAM7A gene product, dupα7, assembles with α7 subunits, resulting in a dominant negative regulation of function. The duplication is human specific, occurring neither in primates nor in rodents. The duplicated α7 sequence in exons 5-10 of CHRFAM7A is almost identical to CHRNA7, and thus is not completely queried in high throughput genetic studies (GWAS). Further, pre-clinical animal models of the α7nAChR utilized in drug development research do not have CHRFAM7A (dupα7) and cannot fully model human drug responses. The wide expression of CHRNA7, its multiple functions and modes of regulation present challenges for study of this gene in disease. This article is part of the Special Issue entitled 'The Nicotinic Acetylcholine Receptor: From Molecular Biology to Cognition'.

Diagnostic specificity and familiality of early versus late evoked potentials to auditory paired stimuli across the schizophrenia-bipolar psychosis spectrum

Disrupted sensory processing is a core feature of psychotic disorders. Auditory paired stimuli (PS) evoke a complex neural response, but it is uncertain which aspects reflect shared and/or distinct liability for the most common severe psychoses, schizophrenia (SZ) and psychotic bipolar disorder (BDP). Evoked time-voltage/time-frequency domain responses quantified with EEG during a typical PS paradigm (S1-S2) were compared among proband groups (SZ [n = 232], BDP [181]), their relatives (SZrel [259], BDPrel [220]), and healthy participants (H [228]). Early S1-evoked responses were reduced in SZ and BDP, while later/S2 abnormalities showed SZ/SZrel and BDP/BDPrel specificity. Relatives' effects were absent/small despite significant familiality of the entire auditorineural response. This pattern suggests general and divergent biological pathways associated with psychosis, yet may reflect complications with conditioning solely on clinical phenomenology.

Auditory M50 and M100 sensory gating deficits in bipolar disorder: a MEG study

OBJECTIVES

Auditory sensory gating deficits have been reported in subjects with bipolar disorder, but the hemispheric and neuronal origins of this deficit are not well understood. Moreover, gating of the auditory evoked components reflecting early attentive stage of information processing has not been investigated in bipolar disorder. The objectives of this study were to investigate the right and left hemispheric auditory sensory gating of the M50 (preattentive processing) and M100 (early attentive processing) in patients diagnosed with bipolar I disorder by utilizing magnetoencephalography (MEG).

METHODS

Whole-head MEG data were acquired during the standard paired-click paradigm in 20 bipolar I disorder patients and 20 healthy controls. The M50 and the M100 responses were investigated, and dipole source localizations were also investigated. Sensory gating were determined by measuring the strength of the M50 and the M100 response to the second click divided by that of the first click (S2/S1).

RESULTS

In every subject, M50 and M100 dipolar sources localized to the left and right posterior portion of superior temporal gyrus (STG). Bipolar I disorder patients showed bilateral gating deficits in M50 and M100. The bilateral M50 S2 source strengths were significantly higher in the bipolar I disorder group compared to the control group.

LIMITATIONS

The sample size was relatively small. More studies with larger sample sizes are warranted. Bipolar subjects were taking a wide range of medications that could not be readily controlled for.

CONCLUSIONS

These findings suggest that bipolar I disorder patients have auditory gating deficits at both pre-attentive and early attentive levels, which might be related to STG structural abnormality.

Maternal smoking during pregnancy and bipolar disorder in offspring

OBJECTIVE

Maternal smoking during pregnancy is associated with a number of adverse externalizing outcomes for offspring from childhood to adulthood. The relationship between maternal smoking and bipolar disorder in offspring, which includes externalizing symptoms among its many manifestations, has not been investigated in depth. The authors examined whether offspring exposed to maternal smoking in utero would be at increased lifetime risk for bipolar disorder after accounting for other factors related to maternal smoking.

METHOD

Individuals with bipolar disorder (N=79) were ascertained from the birth cohort of the Child Health and Development Study. Case subjects were identified by a combination of clinical, database, and direct mailing sources; all case subjects were directly interviewed and diagnosed using DSM-IV criteria. Comparison subjects (N=654) were matched to case subjects on date of birth (±30 days), sex, membership in the cohort at the time of illness onset, and availability of maternal archived sera.

RESULTS

After adjusting for potential confounders, offspring exposed to in utero maternal smoking exhibited a twofold greater risk for bipolar disorder (odds ratio=2.014, 95% confidence interval=1.48-2.53, p=0.01). The associations were noted primarily among bipolar offspring without psychotic features.

CONCLUSIONS

Prenatal tobacco exposure may be one suspected cause of bipolar disorder. However, it will be necessary to account for other unmeasured familial factors before causal teratogenic effects can be suggested.

Biomarkers of bipolar disorder: specific or shared with schizophrenia?

Kraepelin's observations of the differences in the course and outcome of dementia praecox and manic depression fundamentally influenced thinking about bipolar disorder (BP) and schizophrenia (SZ) for over a century. In modern times, there is increasing awareness that a greater understanding of the similarities between these two highly prevalent and disabling conditions can teach us as many lessons about the pathophysiology of severe mental disorders as does the pursuit of differentiating factors. We review publications on developmental, genetic, epidemiological, and outcome research that challenges the Kraepelian dichotomy. We highlight the increasing evidence of the overlap in genetic susceptibility. Neuro-developmental studies provide evidence of shared early pathological processes, whilst neurophysiological investigations also suggest that different genes may have a role in the development of both phenotypes. There is also evidence of overlapping neurocognitive phenotypes. It has become increasingly clear that a simple binary classification of these disorders represents an oversimplification. It may be more apposite to think in terms of genetic influences on six continuous symptom dimensions: neurobiological, cognitive, positive, negative, depressive and manic symptoms.

Schizophrenia and visual backward masking: a general deficit of target enhancement

The obvious symptoms of schizophrenia are of cognitive and psychopathological nature. However, schizophrenia affects also visual processing which becomes particularly evident when stimuli are presented for short durations and are followed by a masking stimulus. Visual deficits are of great interest because they might be related to the genetic variations underlying the disease (endophenotype concept). Visual masking deficits are usually attributed to specific dysfunctions of the visual system such as a hypo- or hyper-active magnocellular system. Here, we propose that visual deficits are a manifestation of a general deficit related to the enhancement of weak neural signals as occurring in all other sorts of information processing. We summarize previous findings with the shine-through masking paradigm where a shortly presented vernier target is followed by a masking grating. The mask deteriorates visual processing of schizophrenic patients by almost an order of magnitude compared to healthy controls. We propose that these deficits are caused by dysfunctions of attention and the cholinergic system leading to weak neural activity corresponding to the vernier. High density electrophysiological recordings (EEG) show that indeed neural activity is strongly reduced in schizophrenic patients which we attribute to the lack of vernier enhancement. When only the masking grating is presented, EEG responses are roughly comparable between patients and control. Our hypothesis is supported by findings relating visual masking to genetic deviants of the nicotinic α7 receptor (CHRNA7).

No effect of polymorphisms in the non-duplicated region of the CHRNA7 gene on sensory gating P50 ratios in patients with schizophrenia and bipolar disorder

Previous research has reported that bipolar disorder and schizophrenic patients evidence sensory gating deficits. The use of intermediate phenotypes may facilitate genetic studies. Four single nucleotide polymorphisms (SNPs) located on the non-duplicated region of the alpha-7 nicotinic receptor gene (CHRNA7) were genotyped in 95 healthy subjects, 127 bipolar disorder and 153 schizophrenic patients. We evaluated the association of these polymorphisms with P50 evoked potential measures. Our results do not support a role for the candidate gene in this neurophysiological disturbance.

Schizophrenia: a neurodevelopmental disorder--integrative genomic hypothesis and therapeutic implications from a transgenic mouse model

Schizophrenia is a neurodevelopmental disorder featuring complex aberrations in the structure, wiring, and chemistry of multiple neuronal systems. The abnormal developmental trajectory of the brain appears to be established during gestation, long before clinical symptoms of the disease appear in early adult life. Many genes are associated with schizophrenia, however, altered expression of no one gene has been shown to be present in a majority of schizophrenia patients. How does altered expression of such a variety of genes lead to the complex set of abnormalities observed in the schizophrenic brain? We hypothesize that the protein products of these genes converge on common neurodevelopmental pathways that affect the development of multiple neural circuits and neurotransmitter systems. One such neurodevelopmental pathway is Integrative Nuclear FGFR1 Signaling (INFS). INFS integrates diverse neurogenic signals that direct the postmitotic development of embryonic stem cells, neural progenitors and immature neurons, by direct gene reprogramming. Additionally, FGFR1 and its partner proteins link multiple upstream pathways in which schizophrenia-linked genes are known to function and interact directly with those genes. A th-fgfr1(tk-) transgenic mouse with impaired FGF receptor signaling establishes a number of important characteristics that mimic human schizophrenia - a neurodevelopmental origin, anatomical abnormalities at birth, a delayed onset of behavioral symptoms, deficits across multiple domains of the disorder and symptom improvement with typical and atypical antipsychotics, 5-HT antagonists, and nicotinic receptor agonists. Our research suggests that altered FGF receptor signaling plays a central role in the developmental abnormalities underlying schizophrenia and that nicotinic agonists are an effective class of compounds for the treatment of schizophrenia.

Genome-wide gene expression in a patient with 15q13.3 homozygous microdeletion syndrome

We identified a novel homozygous 15q13.3 microdeletion in a young boy, with a complex neurodevelopmental disorder characterized by severe cerebral visual impairment with additional signs of congenital stationary night blindness, congenital hypotonia with areflexia, profound intellectual disability, and refractory epilepsy. The mechanisms by which the genes in the deleted region exert their effect are unclear. In this paper, we probed the role of downstream effects of the deletions as a contributing mechanism to the molecular basis of the observed phenotype. We analyzed gene expression of lymphoblastoid cells derived from peripheral blood of the proband and his relatives to ascertain the relative effects of the homozygous and heterozygous deletions. We identified 267 genes with apparent differential expression between the proband with the homozygous deletion and 3 age- and sex-matched typically developing controls. Several of the differentially expressed genes are known to influence neurodevelopment and muscular function, and thus may contribute to the observed cognitive impairment and hypotonia. We further investigated the role of CHRNA7 by measuring TNFα modulation (a potentially important pathway in regulating synaptic plasticity). We found that the cell line with the homozygous deletion lost the ability to inhibit the activation of tumor necrosis factor-α secretion. Our findings suggest downstream genes that may have been altered by the 15q13.3 homozygous deletion, and thus contributed to the severe developmental encephalopathy of the proband. Furthermore, we show that a potentially important pathway in learning and development is affected by the deletion of CHRNA7.

Alpha7 neuronal nicotinic receptors as a drug target in schizophrenia

INTRODUCTION

Schizophrenia is a profoundly debilitating disease that represents not only an individual, but a societal problem. Once characterized solely by the hyperactivity of the dopaminergic system, therapies directed to dampen dopaminergic neurotransmission were developed. However, these drugs do not address the significant impairments in cognition and the negative symptoms of the disease, and it is now apparent that disequilibrium of many neurotransmitter systems is involved. Despite enormous efforts, minimal progress has been made toward the development of safer, more effective therapies to date.

AREAS COVERED

The high preponderance of smoking in schizophrenics suggests that nicotine may provide symptomatic improvement, which has led to investigation for selective molecules targeted to individual nicotinic receptor (nAChR) subtypes. Of special interest is activation of the homomeric α7nAChR, which is widely distributed in the brain and has been implicated in the pathophysiology of schizophrenia through numerous approaches.

EXPERT OPINION

Preclinical and clinical data suggest that neuronal α7nAChRs play an important role in cognitive functions. Moreover, some, but not all, early clinical trials conducted with α7nAChR agonists show cognitive benefits in schizophrenics. These encouraging results suggest that development of compounds targeting α7nAChRs will represent a valuable tool to mitigate symptoms associated with schizophrenia, and open new strategies for better pharmacological treatment of these patients.

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.

A novel approach of homozygous haplotype sharing identifies candidate genes in autism spectrum disorder

Autism spectrum disorder (ASD) is a highly heritable disorder of complex and heterogeneous aetiology. It is primarily characterized by altered cognitive ability including impaired language and communication skills and fundamental deficits in social reciprocity. Despite some notable successes in neuropsychiatric genetics, overall, the high heritability of ASD (~90%) remains poorly explained by common genetic risk variants. However, recent studies suggest that rare genomic variation, in particular copy number variation, may account for a significant proportion of the genetic basis of ASD. We present a large scale analysis to identify candidate genes which may contain low-frequency recessive variation contributing to ASD while taking into account the potential contribution of population differences to the genetic heterogeneity of ASD. Our strategy, homozygous haplotype (HH) mapping, aims to detect homozygous segments of identical haplotype structure that are shared at a higher frequency amongst ASD patients compared to parental controls. The analysis was performed on 1,402 Autism Genome Project trios genotyped for 1 million single nucleotide polymorphisms (SNPs). We identified 25 known and 1,218 novel ASD candidate genes in the discovery analysis including CADM2, ABHD14A, CHRFAM7A, GRIK2, GRM3, EPHA3, FGF10, KCND2, PDZK1, IMMP2L and FOXP2. Furthermore, 10 of the previously reported ASD genes and 300 of the novel candidates identified in the discovery analysis were replicated in an independent sample of 1,182 trios. Our results demonstrate that regions of HH are significantly enriched for previously reported ASD candidate genes and the observed association is independent of gene size (odds ratio 2.10). Our findings highlight the applicability of HH mapping in complex disorders such as ASD and offer an alternative approach to the analysis of genome-wide association data.

Chaperoning α7 neuronal nicotinic acetylcholine receptors

The α7 subtype of nicotinic acetylcholine receptors (AChRs) is one of the most abundant members of the Cys-loop family of receptors present in the central nervous system. It participates in various physiological processes and has received much attention as a potential therapeutic target for a variety of pathologies. The importance of understanding the mechanisms controlling AChR assembly and cell-surface delivery lies in the fact that these two processes are key to determining the functional pool of receptors actively engaged in synaptic transmission. Here we review recent studies showing that RIC-3, a protein originally identified in the worm Caenorhabditis elegans, modulates the expression of α7 AChRs in a subtype-specific manner. Potentiation of AChR expression by post-transcriptional events is also critically assessed.

CHRNA7 haplotypes are associated with impaired attention in euthymic bipolar disorder

BACKGROUND

Bipolar disorder (BD) patients show a deficit in sustained attention during euthymic periods. This deficit may be relevant for genetic studies in these patients. The α7 cholinergic receptor plays an important role in attentional deficit in humans and animal models. Moreover, there is evidence suggesting the role of the alpha 7 nicotinic cholinergic receptor subunit gene (CHRNA7) in BD susceptibility. The aim of the present study was to investigate the impact of CHRNA7 in sustained attention performance.

METHODS

We studied the association of a promoter variant (-86C/T) and three intronic polymorphisms, rs883473, rs6494223 and rs904952, in the non-duplicated region of CHRNA7 with sustained attention in 143 euthymic BD patients (based on DSM-IV criteria) and 101 healthy subjects. Sustained attention was assessed by the degraded stimulus (DS-CPT) version of Continuous Performance Test. Age, gender, years of education and IQ (WAIS vocabulary subtest) were controlled in the analyses as potential confounders.

RESULTS

Several candidate polymorphisms showed significant associations with different measures of the neuropsychological task for bipolar group. The CTCT haplotype was associated with an improvement in the attentional task performance in the BD group (p ≤ 0.025). On the other hand, different low frequency haplotypes showed influence in bipolar attentional performance (p ≤ 0.026).

LIMITATIONS

A replication study using larger samples may be required for conclusive results.

CONCLUSIONS

Our results point toward a slight association of CHRNA7 genotypes and haplotypes with sustained attention performance in euthymic patients with BD.

Evidence for association of the non-duplicated region of CHRNA7 gene with bipolar disorder but not with Schizophrenia

OBJECTIVE

Biological evidence in both human and animal studies suggests α7 neuronal nicotinic acetylcholine receptor subunit gene (CHRNA7) as a suitable functional candidate for genetic studies in psychiatric populations. This gene maps to chromosome 15q13-14, a major linkage hotspot for schizophrenia (SCH) and bipolar disorder (BD). In this study we examine the role of CHRNA7 in influencing the risk of SCH and BD.

METHODS

In the present investigation four SNPs of the non-duplicated region of CHRNA7 were genotyped: -86C/T variant, located in the 5'-upstream regulatory region; and three intronic polymorphisms (rs883473, rs6494223 and rs904952). Genetic analysis was performed on 510 patients diagnosed with SCH, 245 with BD and on 793 unrelated healthy controls.

RESULTS

SNP analysis suggested a significant difference in -86C/T allele (P=0.025) and genotype (P=0.03) frequencies between BD and control groups, although significance was lost after correction for multiple testing. Besides, the nucleotide change (T) in rs6494223 had a protective effect against BD [odds ratio (OR)=0.70 (0.57-0.87); P=0.001]. Genotype frequencies also showed significant association (P=0.001) [CT genotype OR=0.71 (0.5-0.96); TT genotype OR=0.47 (0.29-0.77)]. Haplotypic analysis revealed a positive association of the gene with BD (global-stat=24.18, P value=0.007) with a maximum effect in the region that covered introns 3 and 4. In contrast, no evidence of risk variants was found in the analysis of the SCH sample.

CONCLUSION

Our data support the non-duplicated region of CHRNA7 gene as a susceptibility region for BD but not for SCH. Further genotyping of this region may help to delimit the causal polymorphism.

Probing the relative contribution of the first and second responses to sensory gating indices: a meta-analysis

Sensory gating deficit in schizophrenia patients has been well-documented. However, a central conceptual issue, regarding whether the gating deficit results from an abnormal initial response (S1) or difficulty in attenuating the response to the repeating stimulus (S2), raise doubts about the validity and utility of the S2/S1 ratio as a measure of sensory gating. This meta-analysis study, therefore, sought to determine the consistency and relative magnitude of the effect of the two essential components (S1 and S2) and the ratio. The results of weighted random effects meta-analysis revealed that the overall effect sizes for the S1 amplitude, S2 amplitude, and P50 S2/S1 ratio were -0.19 (small), 0.65 (medium to large), and 0.93 (large), respectively. These results confirm that the S2/S1 ratio and the repeating (S2) stimulus differ robustly between schizophrenia patients and healthy controls in contrast to the consistent but smaller effect size for the S1 amplitude. These findings are more likely to reflect defective inhibition of repeating redundant input rather than an abnormal response to novel stimuli.

Brain size and brain/intracranial volume ratio in major mental illness

BACKGROUND

This paper summarizes the findings of a long term study addressing the question of how several brain volume measure are related to three major mental illnesses in a Colorado subject group. It reports results obtained from a large N, collected and analyzed by the same laboratory over a multiyear period, with visually guided MRI segmentation being the primary initial analytic tool.

METHODS

Intracerebral volume (ICV), total brain volume (TBV), ventricular volume (VV), ventricular/brain ratio (VBR), and TBV/ICV ratios were calculated from a total of 224 subject MRIs collected over a period of 13 years. Subject groups included controls (C, N = 89), and patients with schizophrenia (SZ, N = 58), bipolar disorder (BD, N = 51), and schizoaffective disorder (SAD, N = 26).

RESULTS

ICV, TBV, and VV measures compared favorably with values obtained by other research groups, but in this study did not differ significantly between groups. TBV/ICV ratios were significantly decreased, and VBR increased, in the SZ and BD groups compared to the C group. The SAD group did not differ from C on any measure.

CONCLUSIONS

In this study TBV/ICV and VBR ratios separated SZ and BD patients from controls. Of interest however, SAD patients did not differ from controls on these measures. The findings suggest that the gross measure of TBV may not reliably differ in the major mental illnesses to a degree useful in diagnosis, likely due to the intrinsic variability of the measures in question; the differences in VBR appear more robust across studies. Differences in some of these findings compared to earlier reports from several laboratories finding significant differences between groups in VV and TBV may relate to phenomenological drift, differences in analytic techniques, and possibly the "file drawer problem".

A 15q13.3 homozygous microdeletion associated with a severe neurodevelopmental disorder suggests putative functions of the TRPM1, CHRNA7, and other homozygously deleted genes

We identified a novel homozygous 15q13.3 microdeletion in a young boy with a complex neurodevelopmental disorder characterized by severe visual impairment, hypotonia, profound intellectual disability, and refractory epilepsy. The homozygous deletion of the genes within this deleted region provides a useful insight into the pathogenesis of the observed clinical phenotype. Absence of the Transient Receptor Potential Cation Channel, Subfamily M, Member 1 (TRPM1) gene product is proposed as a possible mechanism for the severe visual impairment; absence of CHRNA7 (alpha7-nicotinic receptor subunit) as a cause of the refractory seizures and severe cognitive impairment; and deletion of MTMR10 and/or MTMR15 (encoding myotubularin related proteins) alone or combined with other homozygously deleted genes as a cause for the congenital hypotonia with areflexia. The distinctive clinical findings in this patient reveal potential functions of the genes within the deleted region.

Schizoaffective disorder - a possible MEG auditory evoked field biomarker

We recorded magnetoencephalographic auditory steady state responses (SSR) from eight schizoaffective (SAD) subjects and compared the resulting data with previously published findings in persons with schizophrenia (SZ) and controls. SAD subjects exhibited SSR responses similar to controls in the left hemisphere and greater than controls in the right hemisphere, whereas SZ subjects exhibited deficits in both amplitude and phase control in both hemispheres. Our findings suggest preservation of GABAergic inhibitory interneuronal control of layer 3 pyramidal cell activity in primary auditory cortex in SAD.

Astrocyte-derived kynurenic acid modulates basal and evoked cortical acetylcholine release

We tested the hypothesis that fluctuations in the levels of kynurenic acid (KYNA), an endogenous antagonist of the alpha7 nicotinic acetylcholine (ACh) receptor, modulate extracellular ACh levels in the medial prefrontal cortex in rats. Decreases in cortical KYNA levels were achieved by local perfusion of S-ESBA, a selective inhibitor of the astrocytic enzyme kynurenine aminotransferase II (KAT II), which catalyses the formation of KYNA from its precursor L-kynurenine. At 5 mm, S-ESBA caused a 30% reduction in extracellular KYNA levels, which was accompanied by a two-threefold increase in basal cortical ACh levels. Co-perfusion of KYNA in the endogenous range (100 nm), which by itself tended to reduce basal ACh levels, blocked the ability of S-ESBA to raise extracellular ACh levels. KYNA perfusion (100 nm) also prevented the evoked ACh release caused by d-amphetamine (2.0 mg/kg). This effect was duplicated by the systemic administration of kynurenine (50 mg/kg), which resulted in a significant increase in cortical KYNA formation. Jointly, these data indicate that astrocytes, by producing and releasing KYNA, have the ability to modulate cortical cholinergic neurotransmission under both basal and stimulated conditions. As cortical KYNA levels are elevated in individuals with schizophrenia, and in light of the established role of cortical ACh in executive functions, our findings suggest that drugs capable of attenuating the production of KYNA may be of benefit in the treatment of cognitive deficits in schizophrenia.

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.

Prepulse inhibition and genetic mouse models of schizophrenia

Mutant mouse models related to schizophrenia have been based primarily on the pathophysiology of schizophrenia, the known effects of antipsychotic drugs, and candidate genes for schizophrenia. Sensorimotor gating deficits in schizophrenia patients, as indexed by measures of prepulse inhibition of startle (PPI), have been well characterized and suggested to meet the criteria as a useful endophenotype in human genetic studies. PPI refers to the ability of a non-startling "prepulse" to inhibit responding to the subsequent startling stimulus or "pulse." Because of the cross-species nature of PPI, it has been used primarily in pharmacological animal models to screen putative antipsychotic medications. As techniques in molecular genetics have progressed over the past 15 years, PPI has emerged as a phenotype used in assessing genetic mouse models of relevance to schizophrenia. In this review, we provide a selected overview of the use of PPI in mouse models of schizophrenia and discuss the contribution and usefulness of PPI as a phenotype in the context of genetic mouse models. To that end, we discuss mutant mice generated to address hypotheses regarding the pathophysiology of schizophrenia and candidate genes (i.e., hypothesis driven). We also briefly discuss the usefulness of PPI in phenotype-driven approaches in which a PPI phenotype could lead to "bottom up" approaches of identifying novel genes of relevance to PPI (i.e., hypothesis generating).

Major psychoses with mixed psychotic and mood symptoms: are mixed psychoses associated with different neurobiological markers?

OBJECTIVE

Evidence related to overlapping clinical and genetic risk factors in schizophrenia and bipolar disorder (BD) have raised concerns about the validity of 'Kraepelinian dichotomy'. As controversies mainly arise in mixed psychoses that occupy the intermediate zone between schizophrenia and BD, investigating neurobiological markers of mixed psychoses may be relevant to understanding the nature of psychotic disorders.

METHOD

In this article, we review studies comparing magnetic resonance imaging, neuropsychological and electrophysiological findings in mixed psychoses with each other, as well as with more prototypical cases of schizophrenia and BD.

RESULTS

The evidence reviewed suggests that mixed psychoses may be associated with different genetic and neurobiological markers compared with prototypical forms of schizophrenia and BD.

CONCLUSION

These findings may be compatible with more sophisticated versions of dimensional and continuum models or, alternatively, they may suggest that there is an intermediate third category between prototypical schizophrenia and BD.

Going up in smoke: tobacco smoking is associated with worse treatment outcomes in mania

BACKGROUND

This study aimed to compare the treatment responses between smokers and non-smokers in bipolar mania clinical trials.

METHODS

Post-hoc analysis was conducted on data collected from three double-blind, randomised controlled trials in bipolar mania that had similar inclusion criteria. Patients were randomised to olanzapine (N=70) or placebo (N=69) for 3 weeks in Trial 1, olanzapine (N=234) or haloperidol (N=216) for 12 weeks in Trial 2, and olanzapine (N=125) or divalproex (N=126) for 47 weeks in Trial 3. This study analysed the Young Mania Rating Scale (YMRS) total scores and Clinical Global Impressions scale for bipolar disorder (CGI-BP) mania severity scores between smokers and non-smokers for each trial and for the pooled data from all three trials, using a mixed-effects model repeated measures approach.

RESULTS

For the pooled data, non-smokers showed superior treatment outcomes on both the YMRS (P=0.002) and CGI-BP (P<0.001), as well as longer time to discontinuation for any cause utilising Kaplan-Meier survival curves. For the individual trials, non-smokers showed greater improvement than smokers on both CGI-BP and YMRS in both treatment arms of Trial 2 (CGI-BP: haloperidol P=0.011, olanzapine P=0.042; YMRS: haloperidol P=0.010, olanzapine P=0.019), and in the olanzapine arm of Trial 3 (CGI-BP: P=0.002; YMRS: P=0.006). No significant difference in outcomes was found between smokers and non-smokers in Trial 1.

LIMITATIONS

Post-hoc design, categorical definition of smoking status, unavailable antipsychotic drug levels, confounding effects of trial medications and substance abuse.

CONCLUSIONS

Smoking appears to be associated with worse treatment outcomes in mania.

Neuronal nicotinic acetylcholine receptors: from the genetic analysis to neurological diseases

Nicotinic acetylcholine receptors (nAChRs) are ligand-gated channels that mediate, in the peripheral nervous system, fast neurotransmission at the neuromuscular junction and in ganglia. Widely expressed in the central nervous system neuronal nAChRs are thought to contribute both to neurotransmission and modulation of neuronal activity. To date, eleven genes encoding for these receptors have been identified in the mammalian genome and their structure is well conserved throughout evolution. Progresses made in the field of genetics and the identification of a large number of small genetic variants such as single nucleotide polymorphisms raise new questions about the physiologic and pharmacologic consequences of such variations. The finding of associations between polymorphisms in the genes encoding for the neuronal nAChRs and neurological disorders such as schizophrenia and Alzheimer disease illustrate the importance of getting a better understanding of these receptors from the gene to function. In this work we present an overview over the progress that has been made in understanding the role of nAChR genes in monogenic disorders such as familial epilepsy, and review the latest knowledge about genetic variants of the nAChR genes and their relationship with common disorders and behavioural traits of complex etiology.

Neurophysiological endophenotypes across bipolar and schizophrenia psychosis

The search for liability genes of the world's 2 major psychotic disorders, schizophrenia and bipolar disorder I (BP-I), has been extremely difficult even though evidence suggests that both are highly heritable. This difficulty is due to the complex and multifactorial nature of these disorders. They encompass several intermediate phenotypes, some overlapping across the 2 psychotic disorders that jointly and/or interactively produce the clinical manifestations. Research of the past few decades has identified several neurophysiological deficits in schizophrenia that frequently occur before the onset of psychosis. These include abnormalities in smooth pursuit eye movements, P50 sensory gating, prepulse inhibition, P300, mismatch negativity, and neural synchrony. Evidence suggests that many of these physiological deficits are distinct from each other. They are stable, mostly independent of symptom state and medications (with some exceptions) and are also observed in non-ill relatives. This suggests a familial and perhaps genetic nature. Some deficits are also observed in the BP-I probands and to a lesser extent their relatives. These deficits in physiological measures may represent the intermediate phenotypes that index small effects of genes (and/or environmental factors). The use of these measures in genetic studies may help the hunt for psychosis liability genes and clarify the extent to which the 2 major psychotic disorders share etio-pathophysiology. In spite of the rich body of work describing these neurophysiological measures in psychotic disorders, challenges remain: Many of the neurophysiological phenotypes are still relatively complex and are associated with low heritability estimates. Further refinement of these physiological phenotypes is needed that could identify specific underlying physiological deficits and thereby improve their heritability estimates. The extent to which these neurophysiological deficits are unique or overlap across BP-I and schizophrenia is unclear. And finally, the clinical and functional consequences of the neurophysiological deficits both in the probands and their relatives are not well described.

Psychiatric genetics: progress amid controversy

Several psychiatric disorders--such as bipolar disorder, schizophrenia and autism--are highly heritable, yet identifying their genetic basis has been challenging, with most discoveries failing to be replicated. However, inroads have been made by the incorporation of intermediate traits (endophenotypes) and of environmental factors into genetic analyses, and through the identification of rare inherited variants and novel structural mutations. Current efforts aim to increase sample sizes by gathering larger samples for case-control studies or through meta-analyses of such studies. More attention on unique families, rare variants, and on incorporating environment and the emerging knowledge of biological function and pathways into genetic analysis is warranted.

P50 sensory gating deficit is a common marker of vulnerability to bipolar disorder and schizophrenia

OBJECTIVE

P50 gating in schizophrenia has contributed much to our understanding of the pathophysiology of the illness. We examined euthymic bipolar patients to determine if they also have a P50 gating deficit.

METHOD

P50 gating was measured in 81 euthymic bipolar patients (50 with a lifetime history of psychotic symptoms), 92 stable schizophrenic patients, and 67 control subjects.

RESULTS

P50 gating was significantly lower in control subjects than in bipolar patients with a lifetime history of psychosis (P = 0.001) and schizophrenic patients (P = 0.0001). In all patient groups, the percentage of patients with P50 gating was higher than in the control group (chi(2) = 30.596; P < 0.0001). There was no statistically significant correlation between P50 gating and other clinical variables.

CONCLUSION

Our data suggest that P50 gating deficit is a neurobiological marker that is present in stable schizophrenic patients and euthymic bipolar patients.