We report here that KOR activation reduced GABAergic synaptic responses whereas KOR blockade increased it, revealing a tonic endogenous KOR activity that suppresses inhibition in the CeA. Dynorphin diminished but did not prevent the ethanol-elicited increase of GABAergic transmission, whereas KOR antagonism blocked the effect of ethanol. We conclude that dynorphin reduces inhibitory transmission and KOR activation tonically controls neuronal activity in the CeA. Dynorphin also antagonizes the effect of ethanol in the CeA of the alcohol-naïve rat brain, suggesting an important role of the dynorphin/KOR system to regulate CeA tone during challenge with ethanol.
