Mechanism of participation of medial preoptic area in the hippocampal inhibition of ovulation.

Bilateral hippocampal (HPC) stimulation with anodal direct current on the afternoon of proestrus blocked spontaneous ovulation in 87.5% of the Wistar rats subjected to the experiments. The incidence of the ovulation block by this procedure was reduced to 16.7% on bilateral injection of 0.25 microgram picrotoxin into the medial preoptic area (mPOA) preceding as well as following the stimulation. Ovulation was also blocked in 53.8% of the animals by bilateral injection of 50.0 microgram GABA into mPOA, while only 20.0% animals showed a blockade of ovulation by saline injection into mPOA. These observations indicate that blockade of ovulation by HPC stimulation can be simulated by local injection of GABA into mPOA while the effect of stimulation can be blocked by local injection of picrotoxin. Thus, indicating the possibility of GABA being neurotransmitter involved at the level of mPOA for mediating the inhibitory hippocampal influence on ovulation.