Effects of courtship on brain gonadotropin hormone-releasing hormone and plasma steroid concentrations in a female amphibian (Taricha granulosa)

Courtship-induced changes in plasma steroid and brain gonadotropin-releasing hormone (GnRH) concentrations in Taricha granulosa were determined with respect to changes in female sexual receptivity. Females were sacrificed at several times after courtship initiation. Concentrations of GnRH (determined by RIA) in the anterior telencephalon were high at courtship initiation (females unreceptive), but decreased by sperm transfer (females receptive). Courtship had no affect on GnRH concentrations in any other brain region examined. Furthermore, courted, receptive females had higher plasma levels of estradiol than did uncourted controls, and estradiol levels remained elevated above control levels 24 hr after courtship initiation. Courtship had no influence on plasma progesterone or corticosterone levels. To determine if the observed changes in GnRH concentrations in the telencephalon were localized to the nervus terminalis, courted females and controls were sacrificed after 5, 20, or 60 min of courtship. Nervus terminalis GnRH concentrations were higher in courted females than in uncourted controls. These results may represent the first documentation of a naturally occurring physiological change in the nervus terminalis.