Chronic testosterone enanthate or estradiol benzoate affects sexual behavior and motivation in Long-Evans rats tested for partner preference.

The present study tested the effects of chronic testosterone enanthate (TE) or estradiol benzoate (EB) on sexual behavior and motivation in female or male Long-Evans rats, respectively. Sexually experienced gonadally intact female rats were treated with TE (4.5 mg/0.1 ml) or oil twice per week for five weeks, whereas sexually experienced gonadally intact male rats were treated with EB (10 μg/0.1 ml) or oil daily for 28 days. On the last day of treatment, subjects were tested for partner preference, whereby subjects could choose to spend time near (no-contact phase) or with (contact phase) either a male or female stimulus. TE-treated females spent less time with the male stimulus during the no-contact phase, but less time with the female stimulus during the contact phase, compared to hormone-primed controls. TE-treated females displayed fewer solicitation behaviors than controls. TE treatment continued for 2 weeks after mating to monitor vaginal estrus. TE-females entered estrus, albeit less frequently than controls. At the end of exposure, body weight was greater, but ovarian weight was lower in TE-treated females than in controls. Conversely, EB-treated males spent more time with the male stimulus and less time with the female stimulus than controls during the contact phase. EB-treated males displayed fewer mounts and took longer to display their first mount. Testes and body weight were lower in EB-treated males than in controls at the end of the treatment period. These results add to our understanding of the effects of opposite-sex hormones on sexual behavior and reproductive physiology using an animal model.