Preference reversals and effects of D-amphetamine on delay discounting in rats

Impulsive choice is correlated with behavioral problems such as attention-deficit/hyperactivity disorder and substance abuse. Effects of stimulant drug administration on impulsive choice are not consistent and may depend on baseline differences in impulsive choice. A within-session delay-discounting procedure in which choice was between one food pellet delivered immediately (impulsive choice) and three food pellets delivered after increasing delays (self-controlled choice) was used to determine effects of adding and subtracting delays common to both reinforcers on impulsive choice in male Sprague-Dawley rats (n=8). Delay discounting was observed and impulsive choice was quantified using area under the curve (AUC). Adding delays common to both reinforcers decreased impulsive choice and subtracting delays common to both reinforcers increased impulsive choice. Before administration of D-amphetamine (0.03-1.80 mg/kg, intraperitoneally), subjects were rank ordered into a low-AUC or a high-AUC group. Select doses of D-amphetamine decreased impulsive choice for subjects in the low-AUC group but not for subjects in the high-AUC group. These results indicate that impulsive choice can be altered by changing the delay common to both reinforcers and suggest that effects of D-amphetamine may depend, in part, on baseline differences in impulsive choice.