Effect of beta-endorphin on sociosexual proclivity in a choice paradigm

Intraventricularly-administered beta-endorphin (beta-END) suppresses receptive and proceptive behaviors of the ovariectomized, estrogen-progesterone-primed rat. This rat model was used in a four-way choice paradigm to investigate the behavioral specificity and motivational aspects of sexual suppression by beta-END. The experimental females showed a preference to associate with a sexually active 'stud' male over the other incentive animals as shown by significantly more approaches to and nose pokes into the stud male compartment. beta-END did not alter that choice preference. Rather, there was a decrease in overall social interaction after beta-END treatment, as shown by decreased total nose pokes. This overall decrease in social motivation, which was blocked by subcutaneous naloxone injection, was not specific to the stud male. It was not a result of akinesia, since total movement among the inner alleys was significantly higher after beta-END treatment, an effect also reversed by naloxone. These data suggest that intraventricular beta-END may act to suppress sociosexual motivation as a whole rather than sexual activity specifically.