Figure 1: Estrogen mediation of high female choice for cocaine over food reinforcement. Males and females (intact or ovariectomized, OVX) are trained to press separate levers for cocaine IV and food reinforcement on alternating sessions under a FR1 schedule of reinforcement (with 20 s time-out) and then are examined for cocaine choice during discrete trials with 25 trials per session [see 27 for details]. (A). Females have higher cocaine choice than do males at 0.4 and 1.0 mg/kg IV cocaine reinforcement; cocaine dose increase cocaine choice in both sexes. (B). OVX abolishes and estrogen replacement (5 μg per day; EB) restores high cocaine choice in females. (C). Estrous cycle stage is not associated with changes in cocaine choice in females. *p < 0.05 versus (intact) females.
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