Peripheral nerves mediating penile erection in the rat

We examined the effects in male rats of bilateral transection of two nerves previously implicated in erectile function, the viscerocutaneous branch of the pelvic nerve (Vc) and the hypogastric nerve (HgN). In Experiment 1 (co nducted in Storrs), males underwent simultaneous or successive section of V e and HgN and were tested for copulation, reflexive erection, and noncontac t erection (NCE), i.e. in response to remote cues from estrous females. NCE is considered to be analogous to 'psychogenic' erection in humans, for whi ch the HgN has been ascribed a significant role. In all three types of test , males had a moderate to severe deficit in erectile function after Vc tran section. Section of HgN alone had no apparent pro- or anti-erectile effect in any context, nor did it affect the decrement resulting from Vc surgery. Regardless of treatment, all groups retained some erectile potential in eac h type of test. The loss of bladder function after Vc surgery and of semina l plug deposition after HgN section gave evidence that the targeted nerves were in fact severed. In Experiment 2 (conducted in Xalapa), males were tes ted only for NCE, but (a) they were tested every 3 days beginning 3 days af ter each surgery, (b) the interval between the two surgeries was more than 2 weeks, rather than 1 week as in Experiment 1, to allow more time for reco very from general effects of surgery and for hypothetical plasticity of neu ral function. In the first test after the first surgery, all groups had a m odest reduction in the proportion of males displaying NCE, relative to sham -operated males. However, this deficit did not extend to measures of NCE la tency or number, and was absent after the second test. After the second sur gery, when all males except those with sham operations had both nerves cut, none of the groups exhibited a significant deficit in NCE, and all groups had at least one test in which at least half the males responded. Thus, (a) HgN section did not significantly impair NCE, reflexive erection, or copul ation; (b) Ve section impaired, but did not eliminate, erection in all thre e contexts, but even those effects may be transient; and (c) transection of both nerves, simultaneously or successively, did not cause a greater impai rment in erection than did cutting just the Vc. We infer that the HgN may h ave no pro-erectile role in erection in rats, even in a model analogous to psychogenic erection. The Vc is probably the most important nerve mediating pro-erectile function in NCE, as in reflexive erection and copulation, but this nerve may not be essential for erection in rats in any context, at le ast in some males. (C) 1999 Elsevier Science B.V. All rights reserved.