Effects of ethanol on hippocampal place-cell and interneuron activity

Mounting evidence suggests that ethanol exerts effects on learning and memo ry by altering cellular activity in the hippocampus and related structures. However, little is actually known regarding ethanol's effects on hippocamp al function in awake, freely-behaving animals. The present study examines t he effects of ethanol on hippocampal place-cell and interneuron activity in freely-behaving rats. Signals from individual hippocampal neurons were iso lated while subjects traversed a symmetric Y-maze for food reward. Followin g 15 min of baseline recording, subjects were injected with one of four dos es of ethanol (0.0, 0.5, 1.0 and 1.5 g/kg), and cellular activity was monit ored for a I-h time period. Following sufficient time for recovery (minimum of 3 h post injection), cellular activity was monitored for an additional 15-min period. Both 1.0 and 1.5 g/kg ethanol potently suppressed the firing of hippocampal place-cells without altering place-field locations. Ethanol did not significantly suppress out-of-field firing rates, leading to a dec rease in spatial specificity (i.e. the ratio of in-field/out-of-field firin g rates). Interneuron activity was not altered by 1.0 g/kg ethanol, but was occasionally suppressed by 1.5 g/kg ethanol. Results are interpreted in li ght of recent behavioral and electrophysiological studies examining the eff ects of ethanol on hippocampal function. (C) 2000 Elsevier Science B.V. All rights reserved.