Female rats acquire cocaine self-administration at a faster rate and a greater percentage of females acquire cocaine self-administration than do male rats (Lynch et al. Psychopharm (1999) 144:77). These sex differences in stimulant self-administration may be due to ovarian hormones, in particular estrogen. For example, self-administration of cocaine varies with estrous cycle (Roberts et al. Psychopharm (1989) 98:408). Also, estrogen increases dopamine release in the nucleus accumbens, a structure implicated in reward-related processes, and potentiates cocaine induced behavioral sensitization (Jackson and Becker, 2001, SFN Abstr). This experiment was conducted to determine whether acute estrogen affects acquisition of cocaine self-administration. Two groups of female rats were used: 1) Ovariectomized (OVX) females treated with vehicle; 2) OVX females treated with 5 μ g estradiol benzoate (OVX-E) 30 min prior to the self-administration session. Rats were trained in 1 hr session on a FR1 schedule, each nose p...