Ethanol-induced changes in the spontaneous activity of single units in the hippocampus of the awake rat: a dose-response study.

The spontaneous firing rates of single units in the dorsal hippocampus of semi-restrained rats chronically prepared with bundles of fine wire niehrome microelectrodes, were monitored during an ethanol challenge. Seven doses of a 25% weight/volume ethanol solution were administered intraperitoneally to all rats, each dose being given on a separate day with an interdose interval of at least 48 hr. Each ethanol injection was preceded by two control recording periods: (1) baseline and (2) saline injection. Sixty-one units from 27 animals were studied with 7–10 units tested at each dose. The results demonstrated that single cells in the hippocampus are sensitive to ethanol, and that this sensitivity which is reflected by a depression in firing rate is dose-dependent with larger doses producing greater degrees of depression. The simultaneously recorded EEG indicated a marked bias in frontal cortical activity towards high amplitude slow waves while the hippocampal activity showed less marked but more varied changes. These findings suggest that the hippocampus is among those structures whose activity and function are particularly sensitive to ethanol, and they demonstrate that a profile of a structure's response to ethanol can be obtained when a sample of neurons is tested at a spectrum of doses.