Female rats pace the rate of copulation, which triggers a neuroendocrine reflex necessary for pregnancy (Erskine, 1989, Horm & Beh (23) 473-502; Adler, 1969, JCPP (69) 613-22). Female rats that are pacing their sexual behavior have increased extracellular dopamine (DA) concentrations in both striatum and nucleus accumbens (NAcc) compared to females who are engaged in nonpaced sexual behavior (Mermelstein & Becker, 1995, Behav Neurosci (109) 354-65). In experiments in which the male is removed for the female at her preferred pacing interval (PPI) during copulation, DA in the NAcc increases as it does in animals engaging in paced sex (Becker et al., 2001, J Neurosci (21) 3236-41). Both paced sex, and sex at the female's PPI, are sufficient to induce a conditioned place preference in the female rat (Jenkins & Becker, 2001, SFN Abstr), suggesting that sex associated with increases in extracellular DA concentrations has reinforcing value for the female. The relationship between DA and reward remains controversi...