AJP - Regulatory, Integrative and Comparative Physiology, Vol 266, Issue 2 606-R613, Copyright © 1994 by American Physiological Society
Endogenous opioids are differentially involved in appetitive and consummatory aspects of sexual behavior of male rats
W. R. Van Furth, I. G. Wolterink-Donselaar and J. M. van Ree
Department of Pharmacology, Rudolf Magnus Institute, University of Utrecht, The Netherlands.
The sexual activity of 40 male Wistar rats was tested weekly in a bilevel
test chamber to evaluate the involvement of endogenous opioids in the
appetitive and consummatory aspects of sexual behavior. It has been
suggested that the increase of the anticipatory level-changing behavior
over repeated testing, displayed before the introduction of a receptive
female, is sexually motivated. Two doses of the opioid antagonist naloxone,
1 and 10 mg/kg, prevented the increase of the anticipatory level-changing
over four repeated tests of sexually experienced rats without prior
experience in the bilevel test chamber and decreased the number of level
changes of rats displaying a high number of level changes. Analysis of the
pattern of inhibition suggested that the lower dose of naloxone may reduce
sexual reward and that, in addition, the higher dose may block the
expression of motivation. In contrast, naloxone treatment facilitated the
efficiency of the sexual performance, with less mounts and intromissions
preceding ejaculation and a shorter ejaculation latency, implying an
inhibitory role of endogenous opioids in the neural control of some aspects
of sexual performance (e.g., ejaculatory threshold). These results suggest
that endogenous opioids may increase sexual appetite and diminish sexual
performance.
