Suppression of precocial copulation by progesterone implants in the male chick forebrain

Precocial copulation in 2-wk.-old male chicks, described behaviorally as free mount, tread, posterior contact, waggle, peek, and seize, was developed through hand-training experience and androgen treatment. Crystalline progesterone was then implanted in various forebrain or midbrain regions. Results indicated that progesterone inhibited copulatory behavior when placed in the periventricular areas of the preoptic-hypothalamic continuum. Progesterone implants in the preoptic lateral forebrain bundle regions also suppressed precocial copulation. Forebrain implants of cholesterol did not result in copulatory inhibition. The suppression of copulatory behavior was not accompanied by loss of weight or deficits in general activity or comb growth. These data indicate that brain regions responsible for progesterone-induced copulatory inhibition are similar in neuroanatomical distribution to those involved in testosterone-induced copulatory activation.