Chronic cocaine exposure in adolescence: Effects on spatial discrimination reversal, delay discounting, and performance on fixed-ratio schedules in mice.

Adolescence is marked by the continued development of the neural pathways that support choice and decision-making, particularly those involving dopamine signaling. Cocaine exposure during adolescence may interfere with this development and manifest as increased perseveration and delay discounting in adulthood, behavioral processes that are related to drug addiction. Adolescent mice were exposed to 30mg/kg/day of cocaine (n=11) or saline vehicle (n=10) for 14days and behavior was assessed in adulthood. In Experiment 1, performance on a spatial-discrimination-reversal procedure was evaluated. In the first two sessions following the first reversal, cocaine-exposed mice produced more preservative errors relative to controls. In Experiment 2, cocaine-exposed mice displayed steeper delay discounting than saline-exposed mice, effects that were reversed by acute cocaine administration. Experiment 3 examined responding maintained by a range of fixed-ratio schedules of reinforcement. An analysis based on a theoretical framework called Mathematical Principles of Reinforcement (MPR) was applied to response-rate functions of individual mice. According to MPR, differences in response-rate functions in adulthood were due to a steepening of the delay-of-reinforcement gradient, disrupted motoric capacity (lower maximum response rates), and enhanced reinforcer efficacy for the adolescent cocaine- compared with saline-exposed mice. Overall, these experiments suggest that chronic exposure to cocaine during adolescence may impair different features of 'executive functions' in adulthood, and these may be related to distortions in the impact of reinforcing events.