Stimulation of the hypothamus initiates the urethrogenital reflex in male rats

Abstract

The urethrogenital (UG) reflex is a spinal sexual reflex which is tonically inhibited in the intact male rat by neurons in the nucleus paragigantocellularis (nPGi). The medial preoptic area of the hypothalamus (MPOA) is involved in the actication of male sexual behavior. The present study examines the effect of hypothalamic stimulation on the UG reflex in the intact male rat. Areas of the hypothalamus were stimulated bilaterally with either electrical stimulation or D,L-homocysteic acid (DLH) and the presence of the UG reflex examined. Stimulation of discrete areas of the hypothalamus evoked the UG reflex. The UG reflex could be initiated in the absence of genital stimulation. Microinjections of DLH into the MPOA also initiate the UG reflex. These data suggest that stimulation of neurons in the MPOA overcome the inhibition by the nPGi and facilitate spinal genital reflexes leading to ejaculation.