Blockade of progesterone-induced increase in hypothalamic luteinizing hormone-releasing hormone levels and serum gonadotropins by intrahypothalamic implantation of 6-hydroxydopamine.
The present study was undertaken to identify the hypothalamic locus where norepinephrine (NE) nerve terminals communicate with luteinizing hormone-releasing hormone (LH-RH)-containing neurons involved in the stimulatory feedback action of gonadal steroids on LH and FSH release. Ovariectomized rats received estradiol benzoate (10 microgram/rat s.c.) on day 0. Intracranial implants containing either 6-hydroxydopamine (6-OHDA), to destroy NE terminals, or cocoa butter (controls) were placed bilaterally in the suprachiasmatic nucleus (SCN), medial basal hypothalamus (MBH) or olfactory tubercle (OT) on day 1. Progesterone (P, 5 mg/rat s.c.) was administered at 10.00 h on day 2 to elicit increases in serum LH and FSH and the MBH LH-RH levels in the afternoon. Implantation of 6-OHDA in the SCN resulted in a marked depletion of NE in and around the region of the SCN in the preoptic-anterior hypothalamic area (POA-AH) without adversely affecting dopamine (DA) concentrations, and blocked the P-induced afternoon increase in the MBH LH-RH and serum gonadotropin levels. Similar reduction in the MBH NE concentrations occurred following placement of 6-OHDA in the MBH; however, these as well as implants in the OT were ineffective in suppressing the P-induced effects. These studies show that functional integrity of the SCN regions is critical in manifestation of the P-induced rise in the MBH LH-RH activity, and this region in the POA-AH, therefore, may be the primary locus of synaptic communication between NE terminals and LH-RH neurons.
D000818:Animals; D002369:Castration; D004298:Dopamine / Q000378:metabolism; D004343:Drug Implants; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D006065:Gonadotropins, Pituitary / Q000097:blood*; D006892:Hydroxydopamines / Q000494:pharmacology*; D007031:Hypothalamus / Q000378:metabolism*; D007033:Hypothalamus, Middle / Q000187:drug effects; D009638:Norepinephrine / Q000378:metabolism; D009830:Olfactory Bulb / Q000187:drug effects; D011301:Preoptic Area / Q000187:drug effects; D011374:Progesterone / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000187:drug effects; D013495:Supraoptic Nucleus / Q000187:drug effects
D004343:Drug Implants; D006065:Gonadotropins, Pituitary; D006892:Hydroxydopamines; D011943:Receptors, Adrenergic, beta; D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone; D004958:Estradiol; D004298:Dopamine; D009638:Norepinephrine