Regulation of noncontact erection in rats by gonadal steroids

Male rats exhibit erections in the presence of inaccessible estrous females , and we investigated which gonadal steroids regulate these noncontact erec tions (NCEs). Sexually experienced Wistar males (n greater than or equal to 8/group) were tested for NCE four times (every 3 days) before castration, after castration, and after receiving subcutaneous implants of 10-mm Silast ic capsules that were empty or filled with crystalline testosterone propion ate (TP), dihydrotestosterone (DHT), estradiol benzoate (EB), or DHT + EB ( 10 mm each). Before castration, males responded with NCE in approximately 5 0% of tests. No males had NCEs after castration, beginning 3 days after sur gery. Also, no males responded after treatment with EB or empty capsules. A fter receiving implants of TP, DHT, or DHT + EB, 50% of males had NCEs, beg inning with the first test 3 days after treatment. On every measure of NCE, males treated with DHT or DHT + EB were indistinguishable from each other and from TP-treated males. Among the sexual responses of male rats, NCE app ears to be more sensitive than other behaviors to changes in gonadal condit ion. In its profile of response to gonadal steroids (testosterones, dihydro testosterone+, estradiol-), NCE is similar to reflexive erection, for which spinal systems are sufficient, and unlike copulation (T+, DHT-, E+), which depends on discrete areas of the brain. We nonetheless conclude that NCE d epends on androgen-sensitive systems in the brain, but androgen-sensitive n eurons in the lumbosacral spinal cord may also play a role. (C) 1999 Academ ic Press.