One-trial behavioral sensitization in preweanling rats: differential effects of cocaine, methamphetamine, methylphenidate, and D-amphetamine.

RATIONALE: Preweanling rats exhibit robust one-trial cocaine-induced behavioral sensitization; however, it is uncertain whether other psychostimulants can also induce sensitization in young rats using the one-trial procedure.
OBJECTIVE: The purpose of this study was to determine whether methamphetamine, methylphenidate, and D: -amphetamine are capable of inducing one-trial locomotor sensitization in preweanling rats.
METHODS: In a series of four experiments, rats were pretreated with cocaine (30 mg/kg), methamphetamine (2-12 mg/kg), methylphenidate (5-20 mg/kg), or amphetamine (5 mg/kg) before being placed in a novel activity chamber or the home cage on PD 19. Rats were then challenged with the same psychostimulant (20 mg/kg cocaine, 1-8 mg/kg methamphetamine, 2.5-7.5 mg/kg methylphenidate, or 1-2 mg/kg amphetamine) on PD 21, with distance traveled being measured for 180 min. In a separate experiment, rats were pretreated with methamphetamine on PD 16-19 and challenged with methamphetamine on PD 21.
RESULTS: Only cocaine, but not various dose combinations of other psychostimulants, was able to produce one-trial behavioral sensitization in preweanling rats. Context-dependent locomotor sensitization was also evident if rats were pretreated with methamphetamine on PD 16-19 and tested on PD 21.
CONCLUSIONS: It is uncertain why only cocaine was able to induce one-trial locomotor sensitization in preweanling rats, but it is possible that: (a) the neural circuitry mediating sensitization differs according to psychostimulant, (b) cocaine is more readily associated with environmental contexts than other psychostimulants, or (c) affinity and pharmacokinetic factors may underlie cocaine's ability to induce one-trial behavioral sensitization in preweanling rats.