Role of monoamines in sexual behavior of the female guinea pig.

Ovariectomized guinea pigs, rendered sexually receptive by injections of estradiol benzoate and progesterone, were treated with drugs that are known to affect monoamine receptor activity. Treatment with the dopamine receptor stimulant apomorphine or the serotonin agonist LSD resulted in a suppression of lordosis behavior that lasted for several hours. The noradrenergic receptor stimulant chlonidine potentiated the performance of lordosis (i.e., increased the duration of individual lordosis responses), while the noradrenergic receptor blocker phenoxybenzamine abolished sexual receptivity. Administration of dopaminergic or serotonergic receptor blockers (pimozide and methysergide, respectively) did not facilitate lordosis. In fact, methysergide produced a brief inhibition of sexual behavior. The results indicate that noradrenergic neurons may be involved in the induction of female sexual behavior in the guinea pig. Dopamine, and possibly serotonin, may serve as transmitters that inhibit lordosis in this species.