Figure 2.

The estrous cycle affected pellet intake and weight gain, but not cocaine intake. (a) The number of pellets earned in the pellet-only sessions was affected by the estrous cycle, whereas there was no effect of preference. In contrast, infusion number was affected by preference, but not the estrous cycle. The lack of a preference effect on pellet intake likely reflects averaging across multiple weeks, during which not all CP females were displaying cocaine preferences. The same effects were observed for intake during choice sessions (data not shown). (b) Weight gain was robustly affected by the estrous cycle in all preference groups, which confirms that females continued to cycle normally throughout self-administration. Therefore, the lack of estrous cycle effects on cocaine intake cannot be attributed to alterations in hormone fluctuations across the cycle (at least in regard to those affecting weight and food intake). Data were averaged across the last 5 weeks of self-administration and aligned to the proestrous/estrous (PE) stage of the cycle. The two days before PE (−2 and −1) correspond with diestrus I and diestrus II, whereas the day after PE (+1) corresponds with metestrus or sometimes estrus (see text for details). Stages without common letters are significantly different from one another. Intake in CP rats was significantly different from PP and ABST rats (*p<0.05 for each). Intake in PP rats was significantly different from CP and ABST rats (^#p<0.05 for each). Vertical lines represent SEM. ABST, abstaining; CP, cocaine preferring.