Rapid BDNF-dependent sequestration of amygdala and hippocampal GABAA receptors via different TrkB-mediated phosphorylation pathways

• Authors: Liping Mou, Emory University; Scott A. Heldt, University of Tennessee; Kerry Ressler, Emory University
• Journal Title: Neuroscience
• Volume: Volume 176
• Publisher: Elsevier: 12 months | 2011-03-10, Pages 72-85
• Type of Work: Article | Post-print: After Peer Review
• Publisher DOI: http://doi.org/10.1016/j.neuroscience.2010.12.041
• Subjects: Biology, Neuroscience
• Keywords: GABAA receptor; BDNF; internalization; Phosphorylation; PKC; PKA; Hippocampus; Amygdala

Abstract

During the consolidation of fear memory, it has been shown that GABAA receptors (GABAAR) are rapidly downregulated in amygdala. This rapid decrease in GABAAR functioning may permit transient hyperexcitablity, contributing to cellular mechanisms of memory consolidation. Memory consolidation also requires BDNF activation of TrkB receptors in the amygdala and hippocampus. We hypothesized that rapid internalization of GABAARα1 is mediated via TrkB activation of PKA and PKC-dependent processes. Primary neuronal cell cultures, from postnatal day 14–21 mouse amygdala and hippocampus, were analyzed with immunofluorescence using cell-surface, whole-cell permeabilization, and antibody internalization techniques, as well as with 3H-muscimol binding assays. In both hippocampal and amygdala cultures, we found a >60% reduction in surface GABAARα1 within 5 minutes of BDNF treatment. Notably, the rapid decrease in surface GABAARα1 was confirmed biochemically using surface biotinylation assays followed by western blotting. This rapid effect was accompanied by TrkB phosphorylation and increased internal GABAARα1 immunofluorescence, and was blocked by k252a, a broad-spectrum tyrosine kinase antagonist. To further demonstrate TrkB specificity, we used previously characterized TrkBF616A mice, in which the highly selective TrkB-mutant specific antagonist, 1NMPP1, prevented the BDNF-dependent GABAARα1 internalization. In hippocampus, we found both PKA and PKC inhibition, using Rp-8-Br-cAMP and Calphostin C, respectively, blocked GABAARα1 internalization, whereas inhibition of MAPK (U0126) and PI3K (LY294002) did not prevent rapid internalization. By contrast in amygdala cultures, Rp-8-Br-cAMP had no effect. Together, these data suggest that rapid GABAAR internalization during memory consolidation is BDNF-TrkB dependent. Further, it appears that hippocampal GABAAR internalization is PKA and PKC dependent, while it may be primarily PKC dependent in amygdala, implying differential roles for TrkB-dependent kinase activation in BDNF-dependent memory formation.