The behavior of cocaine- and pellet-preferring rats diverges after the development of cocaine preferences.

<p>Early in self-administration, there are few differences between pellet preferring (PP) and cocaine preferring (CP) rats in the number of rewards earned during the pellet-only and cocaine-only sessions (A) and choice session (B). Late in self-administration, the behavior of PP and CP rats is different in the pellet-only and cocaine-only sessions (C) and non-overlapping in the choice session (D). Each point represents data from a single male (M) or female (F), whereas the horizontal lines represent the means for each sex collapsed across preference groups (PP- white, CP- black). Significant difference between PP and CP rats (# p<0.05), significant difference between early and late time points in PP (** p<0.05) and CP (* p<0.05) rats, and significant difference between the number of pellets and infusions earned within the choice session or between the two single reward sessions in PP (∧∧ p<0.05) and CP (∧ p<0.05) rats. PP females (n = 6), PP males (n = 10), CP females (n = 6) and CP males (n = 2).