DOI 10.1007/s00213-005-2150-5 ORIGINAL INVESTIGATION

at least five receptor (DAR) isoforms. In female rats, D5 DAR may be involved in expression of sexual behavior. We used a D5 knockout (D5KO) mouse to assess the role of D5 DAR in mouse sexual behavior. Both sexes of D5KO mice are fertile and exhibit only minor disruptions in exploratory locomotion, startle, and prepulse inhibition responses. Objective: This study was conducted to char-acterize the sexual behavior of male and female D5KO mice relative to their WT littermates. Methods: Female WT and D5KO littermates were ovariectomized and given a series of sexual behavior tests after treatment with es-tradiol benzoate (EB) and progesterone (P). Once sexual performance was optimal the dopamine agonist, apomor-phine (APO), was substituted for P. Male mice were ob-served in pair- and trio- sexual behavior tests. To assess whether the D5 DAR is involved in rewarding aspects of sexual behavior, WT and D5KO male mice were tested for conditioned place preference. Results: Both WT and D5KO females can display receptivity after treatment with EB and P, but APO was only able to facilitate receptivity in EB-primed WT, not in D5KO, mice. Male D5KO mice display normal masculine sexual behavior in mating tests. In conditioned preference tests, WT males formed a con-ditioned preference for context associated with either intromissions alone or ejaculation as the unconditioned stimulus. In contrast, D5KO males only showed a place preference when ejaculation was paired with the context. Conclusions: In females, the D5 DAR is essential for the actions of dopamine on receptivity. In males, D5 DAR influences rewarding aspects of intromissions. Taken to-gether, the work suggests that the D5 receptor mediates dopamine’s action on sexual behavior in both sexes, per-haps via a reward pathway