Strain Differences in Patterns of Drug-Intake During Prolonged Access to Cocaine Self-Administration

The current study examined possible interactions between genetic factors and prolonged drug access by testing the Fischer (F344), Lewis (LEW), and Wistar rat strains in a prolonged access cocaine self-administration (SA) procedure. Before prolonged access, the strains did not differ in breakpoints for food or cocaine with progressive ratio (PR) testing. The LEW and Wistar rats acquired cocaine SA faster than the F344s. With prolonged access to cocaine SA, the LEW and Wistar rats showed comparable within-session patterns that were higher at the outset of each session and decreased to a stable baseline. Alternatively, the F344 rats began sessions with lower intake and increased their rate of intake during the session. The F344 and Wistar rats took more drug per session than the LEW rats but did not differ from each other. Following prolonged access, the strains did not differ in breakpoints for food, but the Wistar rats had higher breakpoints for cocaine than the F344 rats. Possible underpinnings for the observed strain differences are discussed.