Erection evoked in male rats by airborne scent from estrous females

In the presence of inaccessible estrous females, male rats display penile erections and associated stereotypic behavior indicative of sexual arousal. The effective stimuli for these noncontact erections (NCEs) had not been determined, but bedding soiled by estrous females was known to be ineffective. The present experiments tested for a potential role for volatile olfactory cues in evoking NCE. In Experiment 1, sexually naive male rats were observed for NCEs when tested with inaccessible, estrous females, upwind (n = 20) or downwind (n = 20) from them under conditions that permitted or prevented visual communication. After half the males in each condition had copulatory experience, they were tested under the same conditions. In each test, only on male of 20 responded with females downwind, whereas about half the 20 males displayed NCEs with females upwind, irrespective of barrier type or, in Test 2, of sexual experience. Olfactory cues from estrous females were apparently necessary to induce NCE, whereas visual and auditory stimuli from estrous were not sufficient to evoke NCE, nor did they affect the response to olfactory stimulation. In Experiment 2, males were downwind from estrous females (n = 10) or anestrous females (n = 10) that were behind opaque barriers and were anesthetized to preclude auditory communication. Results indicated that olfactory cues were also sufficient to provoke NCE in sexually experienced males. Receptive female rats apparently broadcast a volatile pheromone that promotes erection. Pheromones are well known to attract potential mates and to act in concert with other stimuli to promote mating. However, this is the first mammalian evidence for a volatile pheromone acting alone to evoke a sexual fixed-action pattern and, in that sense, acting as an airborne aphrodisiac.