Impact of strain and D-amphetamine on impulsivity (delay discounting) in inbred mice

Rationale Many studies have shown that human drug abusers are more impulsive than nonusers, but the mechanisms underlying this difference are unknown. C57BL/6J (B6) and DBA/2J (D2) mouse strains differ in sensitivity to the associative effects and in self-administration of several drugs of abuse. Objective To determine whether these strains exhibit differences in impulsivity that might correspond to the differences in phenotypes related to drug seeking. Methods We examined impulsive choice in drug-naive B6 and D2 mice using a delay discounting protocol (adjusting amount procedure, J Exp Anal Behav 67:353-366, 1997). Results Contrary to our initial expectations, we observed greater delay discounting (higher impulsivity) in D2 rather than in B6 mice. For both strains, discounting was enhanced by 0.80 and 1.20 mg/kg (i.p.) (D)-amphetamine relative to saline. Conclusions Data demonstrate the sensitivity of the procedure to strain differences and pharmacological manipulations. However, additional data are required to clarify the factors underlying this difference and how the delay discounting measure of impulsivity relates to phenotypic models of drug reinforcement and drug seeking.