Partner preference behavior of estrous female rats affected by castration of tethered male incentives.

Estrous female rats were allowed to interact with either of two tethered intact male rats or to stay in an empty middle part of a three-compartment observation cage during a 60-min test. Sexual interactions occurred with both males (resulting in one to five ejaculations) but most time was spent in the empty compartment. After castration of one of the males, females spent more time with this male than with the intact male, although sexual interactions continued with both incentive animals. This "preference" for the castrated male persisted through the second hour of observation in a second experiment (total test time 115 min) although sexual interactions had virtually ceased during this period. Females' preference for castrated males seemed largely the consequence of aversion to genital stimulation received during intromissions by intact animals: (a) when intromissions were prevented through vaginal occlusion, intact males became by far the preferred partners for the whole 2-hr period of testing while sexual behavior continued to occur throughout the test; (b) when choice was allowed between a testosterone-treated ovariectomized female and an intact male, sexual interaction occurred with both tethered incentive rats but the female became the preferred animal. The results suggest that two opposite tendencies play a role in sexual motivation of estrous female rats: attraction resulting from the action of ovarian hormones on the central nervous system and rejection resulting from genital sensory stimulation through the male's genitalia.