Journal of Neuroscience, Vol 1, 527-531, Copyright © 1981 by Society for Neuroscience
Sequential inhibition of sexual receptivity by progesterone is prevented by a protein synthesis inhibitor and is not causally related to decreased levels of hypothalamic progestin receptors in the female rat
B Parsons and BS McEwen
In the estrogen-primed ovariectomized female rat, the administration of
progesterone facilitates sexual receptivity and activates proceptivity for
many hours. If the progesterone dose is large (e.g., 2.5 mg), a refractory
period follows, during which time animals are less sensitive to additional
progesterone. This refractory period has been termed "sequential
inhibition" and has been correlated previously with decreased levels of
cytosol progestin receptors in the mediobasal hypothalamus-preoptic area
(MBH-POA). Our present results indicate that the "sequential inhibition" of
mating behavior by progesterone appears to involve a protein synthetic step
that is not related causally to decreased levels of cytosol progestin
receptors in the MBH-POA. Animals which received subcutaneous injections of
the protein synthesis inhibitor, anisomycin (100 mg/kg in saline), 15 min
prior to and again 3 hr after progesterone (2.5 mg in propylene glycol)
treatment, displayed greater sexual receptivity at 24 hr than did animals
which received subcutaneous saline injections. However, cytosol progestin
receptor levels in the MBH-POA of animals which received anisomycin plus
progesterone were decreased at 24 hr, relative to animals which received
saline plus progesterone. Anisomycin did not produce positive or negative
behavioral effects at 24 hr when administered 15 min prior to and again 3
hr after propylene glycol, suggesting that the behavioral effects of
anisomycin appear to be related to selective blockade of progesterone
action. In separate experiments, we administered single subcutaneous
injections of anisomycin at various times relative to progesterone (2.5 mg)
treatment. According to the time course of effective anisomycin
application, the presumed protein synthesis which is responsible for the
inhibition of mating behavior occurs between 3 and 13 hr after the
administration of progesterone.