Ethanol inhibits spontaneous activity of central nucleus of the amygdala neurons but does not impair retention in the passive-avoidance task

Background: Behavioral studies using pharmacological manipulations that inc rease neuronal activity of the central nucleus of the amygdala (CeA) have i mplicated the CeA in enhancement of memory modulation. To date, however, th ere has been a dearth of studies investigating the effect of a drug that de creases CeA activity on memory modulation-a drug that inhibits the neuronal activity of the CeA might be expected to impair memory modulation. To dete rmine whether ethanol inhibits CeA activity and, if so, whether decreased C eA activity is associated with impairment of memory modulation, this study investigated the effect of ethanol on spontaneous single-unit activity of C eA neurons and retention in the passive-avoidance task. Methods: The effect of ethanol (0.35, 0.75, 1.5, 2.5 g/kg)was determined on spontaneously firing neurons in the CeA in urethane-anesthetized rats by u se of standard in vivo single-unit electrophysiological recording technique s. Additionally, the effect of ethanol when administered immediately after training in a standard passive-avoidance task was determined on retention t he following day. Results: Ethanol profoundly inhibited spontaneous CeA firing rates in ureth ane-anesthetized rats at all doses tested. Maximal inhibition was related t o dose. Each dose of ethanol significantly inhibited CeA activity within 15 min of administration; within 35 min of administration, 0.75 g/kg of ethan ol inhibited CeA activity by 65.2%, and the highest dose (2.5 g/kg) produce d nearly complete suppression of CeA activity (81.3%). Although ethanol mar kedly inhibited CeA activity, these same doses of ethanol failed to impair retention in the passive-avoidance task: 0.35, 0.75, 1.5, and 2.5 g/kg of e thanol, administered immediately after training, failed to alter latency to step-through the following day. Conclusions: These results show that ethanol profoundly inhibits spontaneou s CeA activity and suggest that inhibition of the CeA is not sufficient to impair retention in the passive-avoidance task.