The suppressant effect of ethanol, delivered via intrahippocampal microdialysis, on the firing of local pyramidal cells in freely behaving rats.

Intrahippocampal microdialysis was performed on 14 freely behaving rats, and the firing of pyramidal cells within the dialysis area was recorded. In one group of rats, the microdialysis was conducted only with artificial cerebrospinal fluid (ACSF) for 2-4 h. In this control group, the recorded neurons displayed normal firing patterns. In another group, ACSF was replaced for 30-60 min with various concentrations of ethanol to deliver this drug via the microdialysis probe into the cell recording area. Ethanol at the concentration of 5% (w/v) significantly and reversibly suppressed the firing of the recorded neurons. The marked firing rate alterations were not accompanied with apparent changes in the hippocampal EEG activity or the behavior of the rats, indicating localized drug actions. These data demonstrate for the first time that in the physiologically functioning brain, ethanol exerts principally a suppressant effect on the electrical activity of hippocampal pyramidal cells.