title: Action of estrogen and mechanical vaginocervical stimulation on the membrane excitability of hypothalamic and midbrain neurons.
abstract: The effect of vaginocervical stimulation (VCS) and estrogen iontophoresis on the electrical activity recorded in urethane-anesthetized female rats from medial preoptic-septal (MPO-S) and midbrain central gray (MCG) neurons was studied during two phases of the estrous cycle, namely metestrus (M) and late proestrus-estrus (LP-E). The spontaneous discharge rate of both MPO-S and MCG neurons varied over the two stages of the estrous cycle. The spontaneous electrical activity of the MPO-S neurons was higher during M than during LP-E whereas MCG unit activity was low during M and higher during LP-E. The VCS-evoked changes in unit activity were specific, in that they were observed in response to mechanical genital stimulation and not in response to painful stimuli and/or nonspecific arousal. These responses were not dependent on the stage of estrous cycle. Finally, the iontophoresis of 17 beta-estradiol hemisuccinate evoked electrophysiological responses from MPO-S and MCG neurons. More MPO-S neurons were responsive to estrogen in LP-E than in M, while fewer MCG neurons were responsive to estrogen in LP-E than in M. The results clearly show that ongoing electrical activity of hypothalamic and midbrain nerve cells can fluctuate between M and LP-E phases of the estrous cycle and change with vaginocervical probing as well as iontophoretically applied estrogen. Furthermore, the results suggest the existence of a reciprocal relationship between the membrane activity of MPO-S and MCG neurons which may be related CNS control of reproductive activities.
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000502:physiology*; D002584:Cervix Uteri / Q000502:physiology*; D004594:Electrophysiology; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D007031:Hypothalamus / Q000166:cytology; D007478:Iontophoresis; D008636:Mesencephalon / Q000166:cytology*; D009474:Neurons / Q000502:physiology*; D010812:Physical Stimulation; D051381:Rats; D011919:Rats, Inbred Strains; D014621:Vagina / Q000502:physiology*
chemical_list: D004967:Estrogens