Noncontact stimulation from estrous females evokes penile erection in rats

Five experiments demonstrated that noncontact stimulation from estrous females evokes penile erection in a high proportion of sexually experienced male rats. In Experiment 1, 23 of 24 males (96%) displayed erections while separated from estrous females by a wire-mesh barrier, compared with 8% when no female was present. In Experiment 2, inaccessible estrous females stimulated erection in 100% of males, whereas only 38% responded to inaccessible unfamiliar males and 0% to inaccessible preferred food or an empty cage (n = 8/group). These data suggest that nonsexual arousing stimuli do not readily evoke erections. Experiments 3 and 4 demonstrated that bedding collected from estrous females is highly attractive to males, but is ineffective in promoting erections even when the males can burrow in the bedding. Therefore, estrous odors alone are apparently insufficient to stimulate erection. In Experiment 5, the percentage of males (n = 18) responding with erection did not vary significantly as a function of their exposure to ovariectomized females (67%), receptive but nonproceptive females (83%), or proceptive females (89%), but these stimuli were progressively more effective in reducing erection latency and increasing the number of erections displayed, suggesting that behavioral cues emitted by females promote erection. The display of erection by rats under the conditions used in these studies satisfies conventional criteria for recognition as psychogenic erections, which we have provisionally defined as erections that occur without concurrent somesthetic stimulation. The availability of a rodent model of psychogenic erection should foster analysis of its physiological mediation.