DIFFERENTIAL PARTICIPATION OF HIPPOCAMPAL-FORMATION IN COCAINE-INDUCED CORTICAL ELECTROENCEPHALOGRAPHIC DESYNCHRONIZATION AND PENILE ERECTION IN THE RAT

We evaluated the role of the hippocampal formation in cocaine-induced cortical electroencephalographic (EEG) desynchronization and penile er ection. Adult, male Sprague-Dawley rats anesthetized and maintained by chloral hydrate were used. Intravenous (1.5 or 3.0 mg/kg) administrat ion of cocaine dose-dependently increased intracavernous pressure (ICP ), our experimental index for penile erection. This was accompanied by desynchronization of EEG activity recorded from the somatosensory cor tex (cEEG), as represented by a decrease in root mean square (RMS) and an increase in mean power frequency (MPF) values. There was a simulta neous increase in the RMS values, without significant changes in the M PF values of EEG signals recorded from the hippocampal formation (hEEG ). In animals that received prior application of 10% xylocaine either intrathecally (i.t.) at the L6-S1 spinal levels or directly into the b ilateral hippocampal formation, the RMS values of both cEEG and hEEG s ignals induced by cocaine (1.5 or 3.0 mg/kg, i.v.) were appreciably re duced, along with a further increase in ICP. Unilateral microinjection of cocaine (15 or 30 mu g) into the hippocampal formation elicited di scernible excitation of both cEEG and hEEG signals. Intriguingly, the ICP underwent a significant and dose-dependent reduction, which was di scernibly antagonized by i.t. application of xylocaine. We conclude th at cocaine may effect cortical EEG desynchronizatian but cause a reduc tion in ICP via an action on the hippocampal formation. Synapse 30:140 -149, 1998. (C) 1998 Wiley-Liss, Inc.