Bilateral lesions restricted to the medial nucleus of the amygdala eliminate mating behavior in the male hamster and severely diminish the male's sniffing and licking investigation of the female hamster's anogenital region. The results suggest that olfactory and vomeronasal sensory information critical to male mating behavior is processed in the medial nucleus, which is an androgen-binding brain area. Thus the medial nucleus may act as a relay through which chemosensory information influences activity in the medial preoptic-anterior hypothalamic junction and the bed nucleus of the stria terminals, areas important in the mediation of male sexual behavior.

Sexual behavior in male hamsters is totally abolished by bilateral removal of the olfactory bulbs. This operation eliminates sensory input from both the olfactory and the vomeronasal systems. We previously demonstrated that peripheral destruction of the olfactory receptors caused anosmia but did not impair male hamster mating behavior. Here we demonstrate that peripheral deafferentation of the vomeronasal system produces severe sexual behavior deficits in approximately one-third of the treated animals. Combined deafferentation of both the vomeronasal and the olfactory systems eliminates copulation in 100 percent of the animals. This is the first experimental demonstration of a functional role for the vomeronasal organ in a mammalian species.

The influence of olfactory bulb removal on running activity, body weight, food and water consumption, and lateral hypothalamic self-stimulation rates was examined in the golden hamster. These experiments attempted to characterize more completely the behavioral and physiological deficits which might be related to the total abolition of male sexual behavior in hamsters produced by ablation of the olfactory bulbs. This operation depressed food consumption and body weight during the first 5-10 postoperative days only and had no effect on water intake. During the same postoperative period, running activity declined by 50% before returning to normal. Self-stimulation rates were reduced below normal during the first 2 postoperative days but returned to preoperative levels by 7 days. These transient effects of bulbectomy on the measured variables were contrasted with the permanent deficit in male sexual behavior which results from olfactory bulb removal.Olfactory bulb ablation dramatically affects a variety of rodent social behaviors. Copulation is eliminated in male hamsters and mice (Murphy & Schneider, 1970;Rowe & Edwards, 1972) and maternal, aggressive, and sexual responsiveness are affected to varying degrees in these and other species