Sensory requirements for noncontact penile erection in the rat

Physical contact is not necessary for male rats to display penile erection when placed in the vicinity of females in estrus (noncontact erection, NCE). The modality and reception of sensory stimuli for the induction of NCE were analyzed. Olfactory bulbectomy eliminated NCE, and destruction of olfactory mucosa by zinc sulfate solution caused a significant suppression of NCE, whereas removal of the vomeronasal organ had no effect. Fresh urine collected from estrous females, but not fresh feces, induced NCE. Neither devocalization of estrous females by cutting the inferior laryngeal nerve nor deprivation of visual cues by placing an opaque barrier between the subjects and stimulus females disrupted NCE. The results indicate that olfactory cues emitted by estrous females induce NCE via the olfactory epithelium. Contrary to what had been suggested by previous experiments, vomeronasal inputs are not indispensable for the induction of NCE.