Action of prolactin, dopamine and LHRH on ventromedial hypothalamic neurons as a function of ovarian hormones.

The effect of iontophoretically-applied prolactin, dopamine, LHRH and LHRH-antagonist analog on the electrical activity of neurons (n = 192) located in the ventromedial nucleus of the hypothalamus (VMH) was studied in untreated and hormone-treated ovariectomized female rats (n = 63). The spontaneous electrical activity of VMH neurons was unaffected by the presence or absence of the ovarian hormones. Neuropharmacological studies indicate that the iontophoretic deposition of prolactin and dopamine produced opposing results, in that prolactin increased the electrical activity of the majority of the VMH neurons tested while dopamine decreased their activity. Finally, the application of LHRH and LHRH-antagonist analog to VMH neurons resulted in a marked suppression of their electrical activity that was even more pronounced in the presence of ovarian hormones. The present work provides evidence at the electrophysiological level of hormonal influences on the responsiveness of VMH neurons to LHRH and its antagonist analog, and demonstrates a relationship between the responsiveness of VMH neurons to prolactin and dopamine.