Molecular evidence for decreased synaptic efficacy in the postmortem olfactory bulb of individuals with schizophrenia

Chronic exposure to MK-801 leads to olfactory deficits and reduced neurogenesis in the olfactory bulbs of adult male mice

Background

MK-801 is a drug widely used in preclinical studies to model schizophrenia in animals. Its distinctive feature is the ability to mimic pathological changes in social interactions. Unlike humans, rodents rely heavily on their sense of smell for social interaction. Since, as previously demonstrated, it also impairs neurogenesis, we set out to determine whether olfactory impairment is associated with chronic administration of the drug.

Methods

The mice were divided into two groups, of which one was administered the drug for 3 weeks, and the other only once. Olfaction and social transfer of food preferences were tested after the drug administration period. At the end of the experiment, an immunofluorescence study was performed to determine differences in neurogenesis in the olfactory bulbs.

Results

An olfactory deficit was observed in animals that received the drug for 3 weeks. These changes were also accompanied by an abnormal lack of food preference in the social transmission test. As a result of a morphological study, a pronounced decrease in the number of new neurons was found in the olfactory bulbs of the animals that had received the drug.

Conclusion

Our results indicate that at least some of the impairments in social behavior of the animals exposed to NMDA receptor antagonists are likely caused by changes in the sense of smell. These changes are associated with disruptions of neurogenesis.

Viral Infections and Schizophrenia: A Comprehensive Review

Schizophrenia is a complex mental disorder with multiple genetic and environmental factors contributing to its pathogenesis. Viral infections have been suggested to be one of the environmental factors associated with the development of this disorder. We comprehensively review all relevant published literature focusing on the relationship between schizophrenia and various viral infections, such as influenza virus, herpes virus 1 and 2 (HSV-1 and HSV-2), cytomegalovirus (CMV), Epstein-Barr virus (EBV), retrovirus, coronavirus, and Borna virus. These viruses may interfere with the normal maturation of the brain directly or through immune-induced mediators, such as cytokines, leading to the onset of schizophrenia. Changes in the expression of critical genes and elevated levels of inflammatory cytokines have been linked to virally-induced infections and relevant immune activities in schizophrenia. Future research is necessary to understand this relationship better and provide insight into the molecular mechanisms underlying the pathophysiology of schizophrenia.

Transcriptional profile of pyramidal neurons in chronic schizophrenia reveals lamina-specific dysfunction of neuronal immunity

While the pathophysiology of schizophrenia has been extensively investigated using homogenized postmortem brain samples, few studies have examined changes in brain samples with techniques that may attribute perturbations to specific cell types. To fill this gap, we performed microarray assays on mRNA isolated from anterior cingulate cortex (ACC) superficial and deep pyramidal neurons from 12 schizophrenia and 12 control subjects using laser-capture microdissection. Among all the annotated genes, we identified 134 significantly increased and 130 decreased genes in superficial pyramidal neurons, while 93 significantly increased and 101 decreased genes were found in deep pyramidal neurons, in schizophrenia compared to control subjects. In these differentially expressed genes, we detected lamina-specific changes of 55 and 31 genes in superficial and deep neurons in schizophrenia, respectively. Gene set enrichment analysis (GSEA) was applied to the entire pre-ranked differential expression gene lists to gain a complete pathway analysis throughout all annotated genes. Our analysis revealed overrepresented groups of gene sets in schizophrenia, particularly in immunity and synapse-related pathways, suggesting the disruption of these pathways plays an important role in schizophrenia. We also detected other pathways previously demonstrated in schizophrenia pathophysiology, including cytokine and chemotaxis, postsynaptic signaling, and glutamatergic synapses. In addition, we observed several novel pathways, including ubiquitin-independent protein catabolic process. Considering the effects of antipsychotic treatment on gene expression, we applied a novel bioinformatics approach to compare our differential expression gene profiles with 51 antipsychotic treatment datasets, demonstrating that our results were not influenced by antipsychotic treatment. Taken together, we found pyramidal neuron-specific changes in neuronal immunity, synaptic dysfunction, and olfactory dysregulation in schizophrenia, providing new insights for the cell-subtype specific pathophysiology of chronic schizophrenia.

Dysfunction of the SNARE complex in neurological and psychiatric disorders

The communication between neurons constitutes the basis of all neural activities, and synaptic vesicle exocytosis is the fundamental biological event that mediates most communication between neurons in the central nervous system. The SNARE complex is the core component of the protein machinery that facilitates the fusion of synaptic vesicles with presynaptic terminals and thereby the release of neurotransmitters. In synapses, each release event is dependent on the assembly of the SNARE complex. In recent years, basic research on the SNARE complex has provided a clearer understanding of the mechanism underlying the formation of the SNARE complex and its role in vesicle formation. Emerging evidence indicates that abnormal expression or dysfunction of the SNARE complex in synapse physiology might contribute to abnormal neurotransmission and ultimately to synaptic dysfunction. Clinical research using postmortem tissues suggests that SNARE complex dysfunction is correlated with various neurological diseases, and some basic research has also confirmed the important role of the SNARE complex in the pathology of these diseases. Genetic and pharmacogenetic studies suggest that the SNARE complex and individual proteins might represent important molecular targets in neurological disease. In this review, we summarize the recent progress toward understanding the SNARE complex in regulating membrane fusion events and provide an update of the recent discoveries from clinical and basic research on the SNARE complex in neurodegenerative, neuropsychiatric, and neurodevelopmental diseases.

Spinophilin expression in postmortem prefrontal cortex of schizophrenic subjects: Effects of antipsychotic treatment

Schizophrenia has been associated with alterations in neurotransmission and synaptic dysfunction. Spinophilin is a multifunctional scaffold protein that modulates excitatory synaptic transmission and dendritic spine morphology. Spinophilin can also directly interact with and regulate several receptors for neurotransmitters, such as dopamine D₂ receptors, which play a role in the pathophysiology of schizophrenia and are targets of antipsychotics. Several studies have thus suggested an implication of spinophilin in schizophrenia. In the present study spinophilin protein expression was determined by western blot in the postmortem dorsolateral prefrontal cortex of 24 subjects with schizophrenia (12 antipsychotic-free and 12 antipsychotic-treated subjects) and 24 matched controls. Experiments were performed in synaptosomal membranes (SPM) and in postsynaptic density fractions (PSD). As previously reported, two specific bands for this protein were observed: an upper 120-130 kDa band and a lower 80-95 kDa band. The spinophilin lower band showed a significant decrease in schizophrenia subjects compared to matched controls, both in SPM and PSD fractions (-15%, p = 0.007 and -15%, p = 0.039, respectively). When schizophrenia subjects were divided by the presence or absence of antipsychotics in blood at death, the lower band showed a significant decrease in antipsychotic-treated schizophrenia subjects (-24%, p = 0.003 for SPM and -26%, p = 0.014 for PSD), but not in antipsychotic-free subjects, compared to their matched controls. These results suggest that antipsychotics could produce alterations in spinophilin expression that do not seem to be related to schizophrenia per se. These changes may underlie some of the side effects of antipsychotics.

Radiological evidence to changes in the olfactory bulb volume depending on body mass index in the childhood

OBJECTIVE

Energy balance is preserved through the exchange between body weight and adipose tissue across the multi-faceted complex network that is composed of the sensorial, metabolic, and neuro-endocrine circuits. The olfactory control of energy homeostasis is maintained through the interplay between the olfactory bulb (OB) and adipose tissue. While extremely studied, most researches still report controversial results and sensorial regulation of obesity is not fully understood. This study aims to investigate the interplay between olfactory bulb volume (OBV) as a radiological clue of sensorial control and obesity in children.

SUBJECTS AND METHOD

Children (n = 195) were classified into four groups based on body mass index (BMI) percentiles: normal weight (n = 89), overweight (n = 31), obese (n = 32) and morbidly obese (n = 43). OBV were calculated using MRI.

RESULTS

Mean OBV was higher in children with obesity than in those of normal weights. The means of OBV are found higher in the overweight and obese children (43.76 ± 9.50-49.29 ± 8.61 mm³) than in those of morbidly obese (38.23 ± 11.52 mm³) (p < 0.001). In overweight and obese children, a positive correlation were found between the BMI and OBV (r_overweigh = 0.275-r_obese = 0.377), while in the morbidly obese group, there was a negative correlation (r_{severelyobese} = -0.445).

CONCLUSION

This study reveals that OBV is higher in obese children. Also, it shows that there is a positive correlation between OBV and BMI in overweight and obese children and a negative correlation in the morbidly obese group. These radiological bimodal changes in OBV indicate that olfactory control acts to provide energy balance, mediated by positive in the overweight and obese children, negative feedback in the morbidly obese group.

CAPON Is a Critical Protein in Synaptic Molecular Networks in the Prefrontal Cortex of Mood Disorder Patients and Contributes to Depression-Like Behavior in a Mouse Model

Aberrant regulation and activity of synaptic proteins may cause synaptic pathology in the prefrontal cortex (PFC) of mood disorder patients. Carboxy-terminal PDZ ligand of NOS1 (CAPON) is a critical scaffold protein linked to synaptic proteins like nitric oxide synthase 1, synapsins. We hypothesized that CAPON is altered together with its interacting synaptic proteins in the PFC in mood disorder patients and may contribute to depression-like behaviors in mice subjected to chronic unpredictable mild stress (CUMS). Here, we found that CAPON-immunoreactivity (ir) was significantly increased in the dorsolateral PFC (DLPFC) and anterior cingulate cortex in major depressive disorder (MDD), which was accompanied by an upregulation of spinophilin-ir and a downregulation of synapsin-ir. The increases in CAPON and spinophilin and the decrease in synapsin in the DLPFC of MDD patients were also seen in the PFC of CUMS mice. CAPON-ir positively correlated with spinophilin-ir (but not with synapsin-ir) in mood disorder patients. CAPON colocalized with spinophilin in the DLPFC of MDD patients and interacted with spinophilin in human brain. Viral-mediated CAPON downregulation in the medial PFC notably reversed the depression-like behaviors in the CUMS mice. These data suggest that CAPON may contribute to aspects of depressive behavior, possibly as an interacting protein for spinophilin in the PFC.

Synapse Pathology in Schizophrenia: A Meta-analysis of Postsynaptic Elements in Postmortem Brain Studies

Changed synapse density has been suggested to be involved in the altered brain connectivity underlying schizophrenia (SCZ) pathology. However, postmortem studies addressing this topic are heterogeneous and it is not known whether changes are restricted to specific brain regions. Using meta-analysis, we systematically and quantitatively reviewed literature on the density of postsynaptic elements in postmortem brain tissue of patients with SCZ compared to healthy controls. We included 3 outcome measurements for postsynaptic elements: dendritic spine density (DSD), postsynaptic density (PSD) number, and PSD protein expression levels. Random-effects meta-analysis (31 studies) revealed an overall decrease in density of postsynaptic elements in SCZ (Hedges's g: -0.33; 95% CI: -0.60 to -0.05; P = .020). Subgroup analyses showed reduction of postsynaptic elements in cortical but not subcortical tissues (Hedges's g: -0.44; 95% CI: -0.76 to -0.12; P = .008, Hedges's g: -0.11; 95% CI: -0.54 to 0.35; P = .671) and specifically a decrease for the outcome measure DSD (Hedges's g: -0.81; 95% CI: -1.37 to -0.26; P = .004). Further exploratory analyses showed a significant decrease of postsynaptic elements in the prefrontal cortex and cortical layer 3. In all analyses, substantial heterogeneity was present. Meta-regression analyses showed no influence of age, sex, postmortem interval, or brain bank on the effect size. This meta-analysis shows a region-specific decrease in the density of postsynaptic elements in SCZ. This phenotype provides an important cellular hallmark for future preclinical and neuropathological research in order to increase our understanding of brain dysconnectivity in SCZ.

Schizophrenia-like olfactory dysfunction induced by acute and postnatal phencyclidine exposure in rats

Deficits in olfactory abilities are frequently observed in schizophrenia patients. However, whether olfactory dysfunction is found in animal models is not known. Here, we examined whether two well-established schizophrenia rat models exhibit olfactory-relevant dysfunction that is similar to schizophrenia patients. Olfactory sensitivity was tested in rats that were acutely (3.3mg/kg) or postnatally (10mg/kg, at postnatal day 7, 9 and 11) treated with phencyclidine (PCP) as schizophrenia models. Electrophysiological recordings were conducted to measure the olfactory-relevant local field potential after acute PCP treatment. Olfactory-relevant neural connections were tested via virus tracing in rats postnatally treated with PCP. We also assessed the reversal effects of olanzapine (OLZ) treatment on both models. We found that acute PCP treatment induced a decline in olfactory sensitivity (p=0.01) and significantly lower beta- and higher gamma-band oscillations (p=0.03, and p=0.00 respectively) which were partly attenuated by OLZ treatment (2mg/kg and 4mg/kg). Postnatal PCP exposure also resulted in an olfactory sensitivity deficit during adulthood (p=0.012 for males and p=0.009 for females), and an abnormal development of neural circuits (p=0.000). Together, our research indicated that olfactory dysfunction found in schizophrenia patients can also be observed on animal models.

Postsynaptic Density-95 Isoform Abnormalities in Schizophrenia

BACKGROUND

Postsynaptic density-95 (PSD-95) protein expression is dysregulated in schizophrenia in a variety of brain regions. We have designed experiments to examine PSD-95 mRNA splice variant expression in the dorsolateral prefrontal cortex from subjects with schizophrenia.

METHODS

We performed quantitative PCR and western blot analysis to measure PSD-95 expression in schizophrenia vs control subjects, rodent haloperidol treatment studies, rodent postmortem interval studies, and GluN1 knockdown (KD) mice vs controls.

RESULTS

We found decreased mRNA expression of beta (t = 4.506, df = 383, P < .0001) and truncated (t = 3.378, df = 383, P = .0008) isoforms of PSD-95, whereas alpha was unchanged. Additionally, we found decreased PSD-95 protein expression in schizophrenia (t = 2.746, df = 71, P = .0076). We found no correlation between PSD-95 protein and alpha, beta, or truncated mRNA isoforms in schizophrenia. PSD-95 beta transcript was increased (t = 3.346, df = 14, P < .05) in the GluN1 KD mouse model of schizophrenia. There was an increase in PSD-95 alpha mRNA expression (t = 2.905, df = 16, P < .05) in rats following long-term haloperidol administration.

CONCLUSIONS

Our findings describe a unique pathophysiology of specific PSD-95 isoform dysregulation in schizophrenia, chronic neuroleptic treatment, and a genetic lesion mouse model of drastically reduced N-methyl-d-aspartate receptor (NMDAR) complex expression. These data indicate that regulation of PSD-95 is multifaceted, may be isoform specific, and biologically relevant for synaptic signaling function. Specifically, NMDAR-mediated synaptic remodeling, and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor trafficking and interaction may be impaired in schizophrenia by decreased PSD-95 beta and truncated expression (respectively). Further, increased PSD-95 beta transcript in the GluN1 KD mouse model poses a potential compensatory rescue of NMDAR-mediated function via increased postsynaptic throughput of the severely reduced GluN1 signal. Together, these data propose that disruption of excitatory signaling complexes through genetic (GluN1 KD), pharmacologic (antipsychotics), or disease (schizophrenia) mechanisms specifically dysregulates PSD-95 expression.

Disrupted Olfactory Integration in Schizophrenia: Functional Connectivity Study

BACKGROUND

Evidence for olfactory dysfunction in schizophrenia has been firmly established. However, in the typical understanding of schizophrenia, olfaction is not recognized to contribute to or interact with the illness. Despite the solid presence of olfactory dysfunction in schizophrenia, its relation to the rest of the illness remains largely unclear. Here, we aimed to examine functional connectivity of the olfactory bulb, olfactory tract, and piriform cortices and isolate the network that would account for the altered olfaction in schizophrenia.

METHODS

We examined the functional connectivity of these specific olfactory regions in order to isolate other brain regions associated with olfactory processing in schizophrenia. Using the resting state functional MRI data from the Center for Biomedical Research Excellence in Brain Function and Mental Illness, we compared 84 patients of schizophrenia and 90 individuals without schizophrenia.

RESULTS

The schizophrenia group showed disconnectivity between the anterior piriform cortex and the nucleus accumbens, between the posterior piriform cortex and the middle frontal gyrus, and between the olfactory tract and the visual cortices.

CONCLUSIONS

The current results suggest functional disconnectivity of olfactory regions in schizophrenia, which may account for olfactory dysfunction and disrupted integration with other sensory modalities in schizophrenia.

Deficits in the identification of pleasant odors predict the transition of an at-risk mental state to psychosis

OBJECTIVE

Existing knowledge of the relationship between olfactory identification (OI) ability and clinical risk of psychosis is inconsistent. To address this inconsistency, the aim of the present study was to identify the relationship between OI ability, with regard to the hedonic attributes of odors, and the risk of transition to psychosis in individuals with an ARMS.

METHODS

A group of 81 individuals meeting the ARMS criteria according to the Comprehensive Assessment of At Risk Mental State were at baseline administered with the University of Pennsylvania Smell Identification Test. The hedonic attributes of odorants were normatively established. Participants were followed up for transition to psychosis for a mean period of 36.1months (SD:27.5months).

RESULTS

The presence of deficits in the identification of pleasant odors was found to be a risk factor for conversion from an ARMS to schizophrenia. The hazard ratio for each point in deficit scores in the Cox regression model was 1.455 (95% CI: 1.211-1.747), p<0.0001. Significant deficits in the identification of pleasant odors were associated with a risk for conversion at both early and late time points from baseline.

CONCLUSIONS

The findings imply that the impaired identification of pleasant odorants may be a risk factor for the transition of an ARMS into a psychotic disorder, and highlights the need for further research of OI in "at-risk" cohorts, taking into account the hedonic attributes of odors.

Emerging Synaptic Molecules as Candidates in the Etiology of Neurological Disorders

Synapses are complex structures that allow communication between neurons in the central nervous system. Studies conducted in vertebrate and invertebrate models have contributed to the knowledge of the function of synaptic proteins. The functional synapse requires numerous protein complexes with specialized functions that are regulated in space and time to allow synaptic plasticity. However, their interplay during neuronal development, learning, and memory is poorly understood. Accumulating evidence links synapse proteins to neurodevelopmental, neuropsychiatric, and neurodegenerative diseases. In this review, we describe the way in which several proteins that participate in cell adhesion, scaffolding, exocytosis, and neurotransmitter reception from presynaptic and postsynaptic compartments, mainly from excitatory synapses, have been associated with several synaptopathies, and we relate their functions to the disease phenotype.

Treating the Synapse in Major Psychiatric Disorders: The Role of Postsynaptic Density Network in Dopamine-Glutamate Interplay and Psychopharmacologic Drugs Molecular Actions

Dopamine-glutamate interplay dysfunctions have been suggested as pathophysiological key determinants of major psychotic disorders, above all schizophrenia and mood disorders. For the most part, synaptic interactions between dopamine and glutamate signaling pathways take part in the postsynaptic density, a specialized ultrastructure localized under the membrane of glutamatergic excitatory synapses. Multiple proteins, with the role of adaptors, regulators, effectors, and scaffolds compose the postsynaptic density network. They form structural and functional crossroads where multiple signals, starting at membrane receptors, are received, elaborated, integrated, and routed to appropriate nuclear targets. Moreover, transductional pathways belonging to different receptors may be functionally interconnected through postsynaptic density molecules. Several studies have demonstrated that psychopharmacologic drugs may differentially affect the expression and function of postsynaptic genes and proteins, depending upon the peculiar receptor profile of each compound. Thus, through postsynaptic network modulation, these drugs may induce dopamine-glutamate synaptic remodeling, which is at the basis of their long-term physiologic effects. In this review, we will discuss the role of postsynaptic proteins in dopamine-glutamate signals integration, as well as the peculiar impact of different psychotropic drugs used in clinical practice on postsynaptic remodeling, thereby trying to point out the possible future molecular targets of "synapse-based" psychiatric therapeutic strategies.

Dysregulations of Synaptic Vesicle Trafficking in Schizophrenia

Schizophrenia is a serious psychiatric illness which is experienced by about 1 % of individuals worldwide and has a debilitating impact on perception, cognition, and social function. Over the years, several models/hypotheses have been developed which link schizophrenia to dysregulations of the dopamine, glutamate, and serotonin receptor pathways. An important segment of these pathways that have been extensively studied for the pathophysiology of schizophrenia is the presynaptic neurotransmitter release mechanism. This set of molecular events is an evolutionarily well-conserved process that involves vesicle recruitment, docking, membrane fusion, and recycling, leading to efficient neurotransmitter delivery at the synapse. Accumulated evidence indicate dysregulation of this mechanism impacting postsynaptic signal transduction via different neurotransmitters in key brain regions implicated in schizophrenia. In recent years, after ground-breaking work that elucidated the operations of this mechanism, research efforts have focused on the alterations in the messenger RNA (mRNA) and protein expression of presynaptic neurotransmitter release molecules in schizophrenia and other neuropsychiatric conditions. In this review article, we present recent evidence from schizophrenia human postmortem studies that key proteins involved in the presynaptic release mechanism are dysregulated in the disorder. We also discuss the potential impact of dysfunctional presynaptic neurotransmitter release on the various neurotransmitter systems implicated in schizophrenia.