Differences in extinction responding and reinstatement of methamphetamine-seeking behavior between Fischer 344 and Lewis rats.

Fischer 344 (F344) and Lewis (LEW) rats differ in a number of self-administration behaviors. Whether or not these strains differ in methamphetamine-primed reinstatement of extinguished responding is unknown. F344 and LEW rats were trained to self-administer intravenous (i.v.) methamphetamine (0.06 mg/kg) during daily 2-h limited access sessions for 14 days. Following methamphetamine self-administration, subjects underwent a minimum of 6 extinction sessions where responding on the previously active lever resulted in no programmed consequences. Following extinction sessions, we evaluated strain and dose dependency of methamphetamine-primed (0.06, 0.12, or 0.24 mg/kg/i.v.) reinstatement of responding. All subjects received each dose once. Dosing order was determined by utilizing a within-subjects Latin square design. We found partial strain differences in daily methamphetamine self-administration. In addition, F344 rats responded significantly more during the first extinction session compared LEW rats. Last, the LEW rats demonstrated a heightened propensity to reinstate responding following methamphetamine priming injections compared to F344 rats. Our results suggest that genetic background influences differences in methamphetamine-seeking behaviors in rats.