Ethanol Increases GABAergic Transmission at Both Pre- and Postsynaptic Sites in Rat Central Amygdala Neurons

We examined the interaction of ethanol with the γ-aminobutyric acid (GABA)ergic system in neurons of slices of the rat central amygdala nucleus (CeA), a brain region thought to be critical for the reinforcing effects of ethanol. Brief superfusion of 11-66 mM ethanol significantly increased GABA type A (GABAA) receptor-mediated inhibitory postsynaptic potentials (IPSPs) and currents (IPSCs) in most CeA neurons, with a low apparent EC50of 20 mM. Acute superfusion of 44 mM ethanol increased the amplitude of evoked GABAAIPSPs and IPSCs in 70% of CeA neurons. The ethanol enhancement of IPSPs and IPSCs occurred to a similar extent in the presence of the GABA type B (GABAB) receptor antagonist CGP 55845A, suggesting that this receptor is not involved in the ethanol effect on CeA neurons. Ethanol superfusion also decreased paired-pulse facilitation of evoked GABAAIPSPs and IPSCs and always increased the frequency and sometimes the amplitude of spontaneous miniature GABAAIPSCs as well as responses to local GABA application, indicating both presynaptic and postsynaptic sites of action for ethanol. Thus, the CeA is the first brain region to reveal, without conditional treatments such as GABABantagonists, consistent, low-dose ethanol enhancement of GABAergic transmission at both pre- and postsynaptic sites. These findings add further support to the contention that the ethanol-GABA interaction in CeA plays an important role in the reinforcing effects of ethanol.