Hyperprolactinemia: its electrophysiologic and pharmacologic effect on neurons of the ventromedial nucleus of the hypothalamus.
Extracellular action potentials were recorded from 691 neurons in the ventromedial hypothalamus (VMH) of urethane anesthetized female rats under acute and chronic sham-operated and hyperprolactinemic conditions. Hyperprolactinemia was produced by transplanting pituitaries under the kidney capsules. Neuronal excitability was recorded and analyzed during spontaneous, baseline activity and following the iontophoretic application of prolactin, dopamine (DA) and luteinizing hormone-releasing hormone (LH-RH). No statistically significant changes were observed in the spontaneous electrical activity of VMH neurons under the conditions tested. Of the responsive neurons, approximately 90% of the neurons recorded and tested with prolactin displayed an increase in firing activity while DA produced a decrease, independent of the endogenous plasma prolactin levels (basal or elevated). However, the response to LH-RH was modified in the chronic hyperprolactinemic animal. The predominant response of VMH neurons to LH-RH in acute sham-operated and hyperprolactinemic as well as in chronic sham-operated animals was one of inhibition, while in the chronic hyperprolactinemic animal, the application of LH-RH initiated excitation rather than inhibition. These results provide evidence that chronic (long-term) exposure to elevated prolactin levels is a sufficient stimulus to modify the neuronal response pattern of VMH nerve cells to iontophoretically applied LH-RH but not to prolactin nor to DA.
D000200:Action Potentials; D000818:Animals; D004298:Dopamine; D005260:Female; D007987:Gonadotropin-Releasing Hormone; D006966:Hyperprolactinemia / Q000503:physiopathology*; D009433:Neural Inhibition; D010902:Pituitary Gland / Q000637:transplantation; D011388:Prolactin; D051381:Rats; D011919:Rats, Inbred Strains; D014697:Ventromedial Hypothalamic Nucleus / Q000503:physiopathology*
D007987:Gonadotropin-Releasing Hormone; D011388:Prolactin; D004298:Dopamine