title: Progestins can have a membrane-mediated action in rat midbrain for facilitation of sexual receptivity.
abstract: In rats, progesterone (P) facilitates sexual receptivity by interacting with intracellular progestin receptors in the ventromedial hypothalamus (VMH). This experiment concerns whether P can also facilitate receptivity in rats by acting extragenomically within the ventral tegmental area (VTA). Ovariectomized rats (n = 10) with bilateral guide cannulas over the VMH and VTA were primed with 2 microg subcutaneous estradiol benzoate 44 hr prior to testing. After a pretest for sexual receptivity, animals received implants to the VMH of P, P conjugated to bovine serum albumin (P:BSA), or cholesterol control (CHOL), and were retested. Two hours later, animals were again tested for receptivity, and P, P:BSA, the P metabolite 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP), or CHOL implants were applied to the VTA. Subjects were retested immediately, 30, 90, and 150 min later. Animals that received P in the VMH and had P, P:BSA, or 3alpha,5alpha-THP applied to the VTA exhibited facilitated receptivity at all time points compared with all other combination implants. That P:BSA and P were equally effective when applied to the VTA, but not the VMH, suggests that in the VTA P's membrane-mediated actions are sufficient to facilitate receptivity, whereas in the VMH they are not. Since the steroid (P) and its metabolite (3alpha,5alpha-THP) are similarly effective when applied to the VTA, given P application to the VMH earlier, P's effects in the VTA may be subsequent to metabolism and/or actions at GABA receptors. Overall, these data suggest that in rats P can act at the membrane of neurons within the VTA to modulate lordosis and that these effects may be subsequent to P's metabolism and/or actions at GABA receptors.
authors.affiliation: Neuroscience Program, Department of Psychology, Connecticut College, New London 06320, USA.
authors.forename: C A
authors.initials: CA
authors.lastname: Frye
authors.forename: S G
authors.initials: SG
authors.lastname: Gardiner
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000187:drug effects*; D005260:Female; D008636:Mesencephalon / Q000187:drug effects*; D011372:Progestins / Q000494:pharmacology*; D051381:Rats; D012726:Sexual Behavior, Animal / Q000187:drug effects*
chemical_list: D011372:Progestins