527. Chronic stress induces region- and cell-type-specific changes in GABAA receptor α-subunit expression in mice

Abstract

Abstract Background Chronic stress is a risk factor for anxiety disorders and depression. These conditions are marked by dysregulated GABAergic (primary inhibitory neurotransmitter) signaling, particularly in the prefrontal cortex (PFC), hippocampus (HPC), and hypothalamus (HPT). Therapeutic interventions, such as benzodiazepines, target the GABAergic receptors but seem to lose efficacy in depressed patients, potentially due to changes in GABAA receptor expression in key regions affected by depression. Aims & Objectives In order to better understand the dynamic changes underlying the reduced efficacy of GABA-targeting drugs in depressed patients, we examined the region- and cell-specific expression of α1, 2, 3, 4, and 5-containing GABAA receptors in a mouse model of chronic stress. We predicted changes in α subunit expression between chronic stress and control groups, particularly marked by decreased α2 expression levels across brain regions. Method C57BL/6J mice (n=64, 2 months old, 50% female) were divided into unpredictable chronic mild stress (UCMS) and control cohorts. UCMS was applied daily for 6 weeks, and anxiety-like phenotype and cognitive performances were assessed. The Phenotyper test was used to measure anxiety phenotype weekly, by measuring avoidance of a light stressor in an automatized, overnight test. Working memory was assessed in the Y maze alternation task. Then blood and brains were collected. Blood was processed to measure corticosterone levels, and brain tissue was processed through RNAscope - an RNA fluorescent in-situ hybridization assay - on PFC, HPT, and HPC sections collected from n=4 per group, using probes for SST, CRH, and GABRA1, 2, 3, 4, and 5 (mRNAs coding for the α1-5 subunits of the GABAA receptor). Slides were imaged and GABRA1, 2, 3, 4, and 5 puncta found inside CRH+, SST+ or SCL17a7 (glutamatergic) cells were quantified. Results UCMS induced gradual anxiety-like phenotype and working memory deficits, associated with elevated corticosterone levels. In the CRH+ cell of the paraventricular nucleus of the HPT, there was a significant decrease in GABRA1 (p=0.01), GABRA2 (p=0.0027) and GABRA4 (p=0.0044) puncta and a significant increase in GABRA3 (p=0.0084) puncta per cell. In the SST+ cell of the PFC, there was a significant increase in GABRA2 puncta (p<0.0001). In the SST+ cell of the HPC, there was a significant decrease in GABRA2 puncta (p<0.0001). In the SCL17a7+ neurons of the PFC and HPC, there was a significant increase in GABRA2 puncta (p<0.001). Discussion & Conclusions GABRA1, 2, 3, 4, and 5 mRNA expression profiles are affected by chronic stress suggesting region- and cell-specific changes to GABAergic signaling caused by stress, potentially explaining pathology and response to GABA-targeting treatments.