Courtship-induced changes in female sexual receptivity : a neuroendocrine study in an amphibian

by Propper, Catherine R.

This thesis describes studies that investigated 1)

the effects of courtship on the neuroendocrine system of

female rough-skinned newts, Taricha granulosa, and 2)

whether the observed courtship-induced neuroendocrine

changes affected female sexual receptivity.

Sexual behaviors of female T. granulosa changed

dramatically during courtship. Initially, females

exhibited unreceptive behaviors to a courting male. After

several hours of courtship, females displayed receptive

behaviors, and males responded by attempting to transfer a

sperm cap. Once courtship, insemination and post-insemination

behaviors were complete, the female no longer

became receptive to future courtship.

Both telencephalic irLHRH and plasma estradiol

concentrations changed as females became receptive. Early

in courtship, when females were unreceptive, irLHRH

concentrations in the telencephalon were elevated, but by

the time females became receptive irLHRH concentrations

were low. The change in telencephalic irLHRH

concentration occurred in the nervus terminalis, a little

understood cranial nerve that may influence reproduction.

Plasma estradiol levels were low at courtship initiation,

but were elevated by the time females became receptive.

The observations, that irLHRH and estradiol concentrations

were associated with changes in female sexual behaviors

and that these hormones influence female sexual

receptivity in other vertebrates, suggested that courtship

by a male activates female sexual behavior by stimulating

endogenous changes in LHRH and estradiol.

Increasing or decreasing plasma estradiol

concentrations or blocking the action of this steroid in

the brain were found to have no effect on female

receptivity. Also, injecting LHRH or LHRH analogs into

brain was found to have no effect on female receptivity.

Progesterone implantation inhibited receptivity suggesting

that this steroid may be responsible for the post-insemination

decrease in female sexual behavior. These

results suggest that although courtship induces

physiological changes in female T. granulosa, the changes

in LHRH and estradiol may not be influencing receptivity.