ERECTION EVOKED IN MALE-RATS BY AIRBORNE SCENT FROM ESTROUS FEMALES

In the presence of inaccessible estrous females, male rats display pen ile 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 kno wn to be ineffective. The present experiments tested for a potential r ole for volatile olfactory cues in evoking NCE. In Experiment 1, sexua lly naive male rats were observed for NCEs when tested with inaccessib le, estrous females upwind (n = 20) or downwind (n = 20) from them und er conditions that permitted or prevented visual communication. After half the males in each condition had copulatory experience, they were retested under the same conditions. In each test, only one male of 20 responded with females downwind, whereas about half the 20 males displ ayed NCEs with females upwind, irrespective of barrier type or, in Tes t 2, of sexual experience. Olfactory cues from estrous females were ap parently necessary to induce NCE, whereas visual and auditory stimuli from estrous females were not sufficient to evoke NCE, nor did they af fect the response to olfactory stimulation. In Experiment 2, males wer e downwind from estrous females (n = 10) or anestrous females (n = 10) that were behind opaque barriers and were anesthetized to preclude au ditory communication. Results indicated that olfactory cues were also sufficient to provoke NCE in sexually experienced males. Receptive fem ale rats apparently broadcast a volatile pheromone that promotes erect ion. Pheromones are well known to attract potential mates and to act i n concert with other stimuli to promote mating. However, this is the f irst mammalian evidence for a volatile pheromone acting alone to evoke a sexual fixed-action pattern and, in that sense, acting as an airbor ne aphrodisiac. (C) 1997 Elsevier Science Inc.