Fig. 2.

Active lever responding and cocaine intake (mg/kg) during acquisition, maintenance, and extinction. A) Daily cocaine intake during the acquisition phase of cocaine self-administration (Days 1–4). Significant differences between animals previously trained to lever press for food pellets (FT) and those that were untrained (UT) are indicated (*p<0.05). B) Active lever responding during acquisition of cocaine self-administration (Days 1–4). C) Daily cocaine intake during the maintenance phase of cocaine self-administration (last 6 days of cocaine self-administration for each animal). D) Active lever responding during the maintenance phase of cocaine self-administration (last 6 days of cocaine self-administration for each animal). E) Active lever responding during the first 7 days of extinction (note: some animals required additional days to meet extinction criteria which are not represented in this figure).