Distinct amygdalar AMPAergic/GABAergic mechanisms promote anxiolitic-like effects in an unpredictable stress model of the hamster.

Abstract

Studies have pointed to both α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) antagonists and GABA(A) receptor (GABA(A)R) agonists as potent antistress agents. In this work, separate subchronic injections of the AMPAR antagonist, 6-ciano-7-nitroquinoxaline-2,3-dione (CNQX), and α1 GABA(A)R subunit agonist (Zol) within the central amygdala nucleus modified the elevated plus maze performances of hamsters exposed randomly to one of the following stressful conditions: food/water deprivation, forced swimming test, and permanence in cold room. Indeed, stressed hamsters treated with CNQX or Zol displayed a very great (p < 0.001) increase of entrance plus a moderate (p < 0.05) time spent into open arms, respectively. At the cellular level, Zol-treated animals supplied a moderately evident argyrophilic reaction (indicative of neurodegeneration) in the hippocampus while it was absent in the hypothalamus. Interestingly, this reaction was significantly reduced by CNQX supporting its preferential protective role. Furthermore, both agents were responsible for a mixed expression pattern of GluR1 and GluR2 mRNA levels in which Zol overall upregulated GluR1 mRNAs, while they were downregulated by CNQX in the hippocampal oriens-pyramidalis layer and in layer III of the cerebral cortex. These findings support the amygdalar AMPAergic protective response against anxiety states in chronically stressed hamsters, which may constitute useful therapeutic strategies for panic-related mood disorders.