GEPHYRIN PLAYS A KEY ROLE IN BDNF-DEPENDENT REGULATION OF AMYGDALA SURFACE GABAARS

Brain-derived neurotrophic factor (BDNF) is critically involved in synaptic plasticity and neurotransmission. Our lab has previously found that BDNF activation of neurotrophic tyrosine kinase, receptor, type 2 (TrkB) is required for fear memory formation and that GABA(A) receptor (GABA(A)R) subunits and the GABA(A) clustering protein gephyrin are dynamically regulated during fear memory consolidation. We hypothesize that TrkB-dependent internalization of GABA(A)Rs may partially underlie a transient period of amygdala hyperactivation during fear memory consolidation. We have previously reported that BDNF modulates GABA(A)R alpha 1 subunit sequestration in cultured hippocampal and amygdala neurons by differential phosphorylation pathways. At present, no studies have investigated the regulation of gephyrin and GABA(A)R alpha 1 subunits following BDNF activation in the amygdala. In this study, we confirm the association of GABA(A)R alpha 1 and gamma 2 subunits with gephyrin on mouse amygdala neurons by coimmunoprecipitation and immunocytochemistry. We then demonstrate that rapid BDNF treatment, as well as suppression of gephyrin protein levels on amygdala neurons, induced sequestration of surface alpha 1 subunits. Further, we find that rapid exposure of BDNF to primary amygdala cultures produced decreases in gephyrin levels, whereas longer exposure resulted in an eventual increase. While total alpha 1 subunit levels remained unchanged, gephyrin was downregulated in whole cell homogenates, but enhanced in complexes with GABA(A)Rs. Our data with anisomycin suggest that BDNF may rapidly induce gephyrin protein degradation, with subsequent gephyrin synthesis occurring. Together, these findings suggest that gephyrin may be a key factor in BDNF-dependent GABA(A)R regulation in the amygdala. This work may inform future studies aimed at elucidating the pathways connecting BDNF, GABA(A) systems, gephyrin, and their role in underlying amygdala-dependent learning. (C) 2013 IBRO. Published by Elsevier Ltd. All rights reserved.