Effects of hormones and vaginal stimulation on the EEG and hypothalamic units in rats

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Abstract
In female rats under light urethane anesthesia, a study has been made of the effects of vaginal stimulation and intravenous injections of progesterone and luteinizing hormone (LH) on cerebral activity as represented by both the cortical eeg and hypothalamic unit firing rates. The results reveal that: stimulation of the vaginal cervix during late diestrus-early proestrus induces an "afterreaction" characterized by the induction of a "sleepy" eeg and a temporally correlated effect on unit firing rates, usually involving a depression in frequency; intravenous injections of progesterone in dosages as low as 100 ug exert brief generalized anesthetic effects on eeg and unit firing rates; intravenous LH exerts a relatively specific effect on basal hypothalamic neuron firing rates independent of eeg changes, an effect consistent with the hypothesis that the LH is acting as an internal negative feedback agent on the hypothalamic neurons controlling pituitary LH secretion. The results emphasize that in studies of specific actions of hormones on individual neurons it is essential to monitor the eeg as a control for generalized influences.