ELECTROPHYSIOLOGICAL STUDIES ON THE FEED-BACK MECHANISM OF PROGESTERONE

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Abstract
To clarify the functional relation between the ovulation blocking-effect and the central depressant action of progesterone, electrophysiological studies were done, using unanesthetized curarized albino rats under artificial respiration, additionally using rabbits and cats, and the following results were obtained: (1) After the administration of progesterone (10-20 mg/kg), EEG of the hippocampus and neocortex showed sleep patterns, lasting 1 hr.. (2) Activation threshold of posterior hypothalamic stimulation upon the hippocampus and neocortex was markedly elevated after the administration of progesterone. (3) The threshold voltage desynchronizing the hippo-campal regular slow waves by anterior hypothalamic stimulation remained almost unchanged. (4) The threshold voltage of the recruiting response of the neocortex by stimulation of uncus centrum medianum was almost unchanged. From these results it is concluded that progesterone seems to suppress the activity level of the posterior hypo-thalamus as well as that of the limbic-midbrain area (Nauta, 1958) by which the blockade of ovulation may take place.