Role of TLR4 in the Modulation of Central Amygdala GABA Transmission by CRF Following Restraint Stress

Aims: Stress induces neuroimmune responses via Toll-like receptor 4 (TLR4) activation. Here, we investigated the role of TLR4 in the effects of the stress peptide corticotropin-releasing factor (CRF) on GABAergic transmission in the central nucleus of the amygdala (CeA) following restraint stress. Methods: Tlr4 knock out (KO) and wild-type rats were exposed to no stress (nave), a single restraint stress (1 h) or repeated restraint stress (1 h per day for 3 consecutive days). After 1 h recovery from the final stress session, whole-cell patch-clamp electrophysiology was used to investigate the effects of CRF (200 nM) on CeA GABAA-mediated spontaneous inhibitory postsynaptic currents (sIPSCs). Results: TLR4 does not regulate baseline GABAergic transmission in the CeA of naive and stresstreated animals. However, CRF significantly increased the mean sIPSC frequencies (indicating enhanced GABA release) across all genotypes and stress treatments, except for the Tlr4 KO rats that experienced repeated restraint stress. Conclusions: Overall, our results suggest a limited role for TLR4 in CRFs modulation of CeA GABAergic synapses in nave and single stress rats, though TLR4-deficient rats that experienced repeated psychological stress exhibit a blunted CRF cellular response. Short Summary: TLR4 has a limited role in CRFs activation of the CeA under basal conditions, but interacts with the CRF system to regulate GABAergic synapse function in animals that experience repeated psychological stress.