Inhibition of gonadotropin secretion induced by stimulation of thalamic nuclei.

The effect of electrochemical stimulation (anodic current, 100 micronA/30 sec) of thalamic nuclei was studied in nonanesthetized freely-behaving rats bearing chronic implanted electrodes and plastic cannulae inserted into the jugular vein for blood sampling. Stimulation of the anterior thalamic nuclei, the nucleus (n.) mediodorsalis thalami (MD) and the n. posteromedianus thalami at 2 p.m. on the day of proestrus prevented spontaneous ovulation and the release of LH which takes place on that day. No effect on ovulation or LH release was observed after stimulation of the n. lateralis thalami, the n. ventralis thalami or other thalamic nuclei or after passing a cathodic current through the n. MD. Stimulation of the n. MD resulted also in a significant decrease of the elevated serum LH levels found after an injection of progesterone into ovariectomyzed estrogen-primed rats. These results indicate that nuclei of the medial thalamic region are capable of inhibiting LH secretion. No stimulatory influence of LH release was observed after thalamic stimulation in ovariectomized estrogen-treated rats.