STIMULATION OF THE HYPOTHALAMUS INITIATES THE URETHROGENITAL REFLEX IN MALE-RATS

The urethrogenital (UG) reflex is a spinal sexual reflex which is toni cally inhibited in the intact male rat by neurons in the nucleus parag igantocellularis (nPGi). The medial preoptic area of the hypothalamus (MPOA) is involved in the activation of male sexual behavior. The pres ent study examines the effect of hypothalamic stimulation on the UG re flex in the intact male rat. Areas of the hypothalamus were stimulated bilaterally with either electrical stimulation or D,L-homocysteic aci d (DLH) and the presence of the UG reflex examined. Stimulation of dis crete areas of the hypothalamus evoked the UG reflex. The UG reflex co uld be initiated in the absence of genital stimulation. Microinjection s of DLH into the MPOA also initiate the UG reflex. These data suggest that stimulation of neurons in the MPOA overcome the inhibition by th e nPGi and facilitate spinal genital reflexes leading to ejaculation.