| Abstract No.: | C-B3048 |
| Country: | Canada |
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| Title: | REGIONAL HIPPOCAMPAL DECREASE IN VESICULAR GLUTAMATE TRANSPORTER 1 (VGLUT1) EXPRESSION IN MICE WITH NATURAL MUTATION IN DYSBINDIN-1 GENE |
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| Authors/Affiliations: | 1 Lina Marsan*; 1 Marc Danik; 1 Lalit K. Srivastava; 1 Sylvain Williams;
1 Douglas Mental Health University Institute, McGill University, Department of Psychiatry, Montreal, QC, Canada
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| Content: | Objectives: Genetic studies in a number of populations have revealed polymorphisms in dystrobrevin binding protein-1 (DTNBP-1), a gene encoding dysbindin-1, as a potential risk factor for schizophrenia. Significant levels of dysbindin-1 mRNA and protein expression has been detected in the mouse brain and dysbindin-1 protein is highly expressed, more exclusively in neurons, both pre- and post-synaptically. Postmortem analysis of brains of patients diagnosed with schizophrenia showed a reduction in dysbindin-1 protein expression in certain brain structures, notably the hippocampus and prefrontal cortex. Dysbindin-1 has been linked to glutamatergic transmission however the possible mechanisms by which its down-regulation mediates the aberrant cortical/limbic glutamatergic synapses in schizophrenia are still unknown. Using a mouse model with a natural deletion in the dysbindin-1 gene, we studied hippocampal subregional differences in vesicular glutamate transporter 1 (vGLUT1) expression, the protein that plays a key role in packaging glutamate in the vesicles, and compared it to the vesicle marker synaptophysin (SYP).
Materials and Methods: Double-labeling fluorescent immunohistochemical analysis for vGLUT1 (secondary antibody: CY3) and SYP (secondary antibody: Alexa 488) were performed on P21-23 wild-type DBA/2J and DBA/2J mice with natural heterozygous (SDY/+) and homozygous (SDY/SDY) mutations of DTNBP-1 (n=2/genotype). Mice were decapitated and brains were postfixed by immersion in 4% paraformaldehyde (PARA) overnight, transferred to 15% sucrose solution overnight, and lastly 30% sucrose solution overnight (all at 4°C). Brains were sliced into 20μm coronal sections at the level of the hippocampus. Subregional intensity line profile analysis of Cornu Ammonis 1 and 3 (CA1, CA3; stratum alveus-oriens, pyramidal cell layer, stratum radiatum, and stratum lacunosum-moleculare), and Dentate Gyrus (DG; granular cell layer, molecular layer, hilus, and polymorphic layer) was conducted using Image J over a regional representative area of 4500μm2.
Results: We found that expression of SYP and vGLUT1 across subregions of the CA1, CA3 and DG did not significantly differ in SDY/+ compared to DBA/2J. Interestingly, SDY/SDY mice displayed significantly lower expression of SYP and vGLUT1. This decrease was comparable across all subregions of the hippocampus.
Conclusion: The present study provides evidence supporting the role of dysbindin-1 in glutamatergic synapses. For the first time in this animal model of schizophrenia, we have shown the possible involvement of dysbindin-1 in the destabilization of glutamate vesicular trafficking. The reductions of dysbindin-1 expression observed in schizophrenia perhaps contribute to the schizophrenia pathogenesis and glutamate hypofunction by decreasing the number of glutamatergic synaptic vesicles or vesicular glutamate content. In a future study, we will perform in vitro electrophysiological recordings on hippocampal slices of DBA/2J, SDY/+ and SDY/SDY mice to investigate whether the decrease in the vGLUT1 expression has a significant effect on glutamatergic synaptic transmission in the hippocampal circuits.
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