Effects of Electrochemical Stimulation of the Ventral Hippocampus on Hypothalamic Electrical Activity and Pituitary Gonadotropin Secretion in Female Rats

Abstract

Application of an anodal DC electrochemical stimulus to the ventral hippocampus (VHPC) produced changes in the multiple unit activity (MUA) of the arcuate (ARH) and ventromedial hypothalamic nuclei and in tonic and cyclic mechanisms controlling release of pituitary LH in female rats. In ovariectomized estrogen-primed rats, both hypothalamic nuclei responded to VHPC stimulation in less than 6 min with increases in MUA which persisted for hours. The effect was apparently due to the deposition of iron since stainless steel electrodes were effective while platinum electrodes were not. This response was dependent on the presence of an intact medial corticohypothalamic tract, and it did not occur in the dorsomedial hypothalamus, zona incerta or median eminence. Stimulation of the VHPC region which increased ARH neuronal activity also resulted in a significant decrease in plasma LH within 3 hr after its application. Stimulation of the caudate nucleus or mere insertion of electrodes into the VHPC did not lower plasma LH levels. VHPC stimulation prevented spontaneous ovulation in proestrous rats but did not inhibit ovulation induced by medial preoptic area (MPOA) stimulation in pentobarbital-blocked rats. Thus, following VHPC stimulation an increase in MUA can occur in the ARH at a time when inhibition of the LH release mechanism takes place. Results support the tentative hypothesis of 2 opposing pools of neurons in the arcuate nucleus. (Endocrinology89: 704, 1971)