Effects of Cortical Spreading Depression on Multiunit Activity in the Preoptic Area and Hypothalamus of the Female Rat

Abstract

A study was made of the effects of cortical spreading depression (SD) on the multiunit activity (MUA) of the medial preoptic area and ventromedial hypothalamus in female rats under acute (cycling) and chronic (PMS-HCG treated) conditions. During ‘spontaneous’ slow wave EEG activity under urethane anesthesia or slow wave sleep in freely moving rats, the MUA showed lower levels of integrated and spike firing activity than during fast wave EEG desynchrony. The application of either 2 or 25 % KCl directly onto the exposed dura in the acute preparation or through a permanently implanted cerebral cannula in the ‘chronic’ animal induced a progressive drop in EEG amplitude and a decrease in MUA (both integrated and spike pulses) from the recorded brain regions. The MUA reached its lowest activity 2–3 min after KCl treatment regardless of the location of the cortical area to which the KCl was applied. Recovery was reached progressively after 15–20 min and somewhat earlier in chronic preparations. During the recovery period EEG spikes were observed accompanied by sudden, brief increases in MUA. All of these changes were elicited regardless of the hormonal condition. When considered in the light of previous results in which a release of gonadotropins was associated with cortical SD, the present findings suggest the possibility that cortical SD depresses inhibitory pathways or mechanisms at the MPO-hypothalamic level, resulting in enhancement of release of pituitary gonadotropins.