Mounting and Brief Noncontact Exposure of Males to Receptive Females Facilitate Reflexive Erection in Rats, Even After Hypogastric Nerve Section

Abstract

In three experiments, reflexive erection in male rats was facilitated by housing the males for 2 min with inaccessible sexually receptive females. In Experiment 1, males were sexually naive or experienced and received two reflexive erection tests, 1 week apart, immediately after the males were exposed to receptive females, to unreceptive females, or to no females ( n = 8 per group). In both tests, experienced males exposed to estrous females had the shortest reflexive erection latencies; in Test 1 the differences among groups were of borderline significance ( p = 0.057), but in Test 2 the differences among groups were highly reliable ( p < 0.01). Further analysis indicated that only experienced males exposed to receptive females were significantly different from other groups. In Experiment 2, sexually experienced males ( n = 11) received four reflexive erection tests: after being with no female, and 0, 5, or 10 min after exposure to estrous females. As the interval between exposure and test increased, the males had progressively shorter erection latencies ( p < 0.01) and more intense glans erections ( p < 0.03). Experiments 1 and 2 may be viewed as demonstrating the psychogenic facilitation of reflexive erections. In Experiment 3, males underwent sham surgery (sham, n = 10) or bilateral transection of the hypogastric nerves (HgNx, n = 10), which are conventionally viewed as mediating psychogenic erection. After males mounted a receptive female for 5 min without intromission or had 2 min of noncontact exposure to receptive females, the males had shorter erection latencies ( p < 0.001) and more erections ( p < 0.02). These facilitative effects of pretest stimulation were unaffected by HgN transection. During copulation tests, HgNx males had longer ejaculation latencies ( p < 0.05) and lower intromission ratios ( p < 0.05), possible signs of impaired erectile function. However, in Experiment 4, other males were tested twice for reflexive erection and copulation after sham ( n = 8) or HgNx ( n = 9) surgery, and there were no significant effects of surgery on reflexive erection or copulatory behavior. Collectively, these experiments indicate (a) that brief noncontact exposure of sexually experienced males to estrous females facilitates reflexive erection, (b) that this facilitation increases for at least 10 min after the females are removed, and (c) that the hypogastric nerves do not mediate these facilitative effects. The evidence for a role for the HgN in copulation was inconclusive.