8-OH-DPAT interacts with sexual experience and testosterone to affect ejaculatory response in rats

Studies investigating the effect of 8-OH-DPAT (DPAT) on male sexual response have typically used subjects having variable sexual experience and levels of testosterone, factors known to independently influence male sexual behavior. This experiment examined the role of these two variables in the mediation of DPAT effects on sexual behavior. One hundred and six castrated males, half of whom received sexual experience, were tested with an effective dose of 8-OH-DPAT (0.1 mg/kg) or saline. In addition, males were tested under one of three regimens of testosterone. Results indicated that DPAT and testosterone exerted independent effects on ejaculatory measures, and along with sexual experience, showed interactive effects as well. When testosterone (T) levels were substantially below normal, DPAT showed no effect. When T reached threshold levels, the DPAT effect was limited to sexually experienced males. At high T levels, both experienced and naive males exhibited strong effects from DPAT. In contrast with ejaculatory measures, mounting and intromitting behaviors were relatively unaffected by DPAT. These results emphasize the importance of specifying both the animal's sexual history and its testosterone profile in studies investigating pharmacological effects on sexual response. (C) 1998 Elsevier Science Inc.