High impulsivity in rats predicts amphetamine conditioned place preference

Abstract

Stimulants such as d-amphetamine (AMPH) are used commonly to treat attention-deficit hyperactivity disorder (ADHD), but concerns have been raised regarding the use of AMPH due to its reinforcing and potentially addictive properties. The current study examined if individual differences in impulsive choice predict AMPH-induced hyperactivity and conditioned place preference (CPP). Rats were first tested in delay discounting using an adjusting delay procedure to measure impulsive choice and then were subsequently tested for AMPH CPP. High impulsive (HiI) and low impulsive (LoI) rats were conditioned across four sessions with 0.1, 0.5, or 1.5 mg/kg of AMPH. AMPH increased locomotor activity for HiI and LoI rats following 0.5 mg/kg but failed to increase activity following 0.1 and 1.5 mg/kg. CPP was established for HiI rats with both 0.5 and 1.5 mg/kg of AMPH, whereas LoI rats did not develop CPP following any dose of AMPH; HiI and LoI groups differed significantly following 0.5 mg/kg of AMPH. These results indicate that HiI rats are more sensitive to the rewarding effects of AMPH compared to LoI rats, which is consistent with research showing that high impulsive individuals may be more vulnerable to stimulant abuse.

Fig. 1

MAD scores (mean ± SEM) for high impulsive (HiI; n=18) and low impulsive (LoI; n=18) rats, defined as the top and bottom thirds across all rats tested in Experiments 1–3. *p<.005, compared to HiI following Bonferroni correction.

Fig. 2

a Total number of photobeam breaks (mean ± SEM) for rats (n=12) on sessions following 0.1 mg/kg of AMPH or SAL in Experiment 1. b Total number of photbeam breaks (mean ± SEM) for rats (n=12) on sessions following 0.5 mg/kg of AMPH or SAL in Experiment 2. c Total number of photobeam breaks (mean ± SEM) for rats (n=12) on sessions following 1.5 mg/kg of AMPH or SAL in Experiment 3. *p<.01, compared to SAL following Bonferroni correction. #p<.05, compared to Session 1.

Fig. 3

Difference score for HiI (n=6 per dose) and LoI (n=6 per dose) rats; each dose was tested in a separate experiment. A difference score of 0 indicates no preference for either chamber, a difference score above 0 indicates a preference for the chamber previously paired with AMPH, and a difference score below 0 indicates a preference for the chamber previously paired with SAL. *p<.05, compared to a difference score of 0; **p<.01, compared to a difference score of 0; #p<.05, compared to LoI.