Rationale-Methamphetamine (METH) is typically characterized as a more potent psychostimulant than amphetamine (AMPH), but few studies have directly compared the effects of these drugs at low, behaviorally activating doses that tend not to produce focused stereotypy.Objectives-To compare the effects of AMPH or METH treatment on locomotor activity in an open-field arena, focusing on their ability to produce conditioned locomotor activity, sensitization, and cross-sensitization.Methods-Adult male rats were given AMPH or METH (0.5 or 1.0 mg/kg) for five days, with half of the rats presented with discrete, salient stimuli (S+) during the post-injection period. Following a three-day withdrawal, they were given three different injections on successive days: a saline challenge to assess conditioned responding, a drug challenge to assess sensitization, and a crosssensitization test to the same dose of the drug with which they were not pre-treated.Results-Except in certain conditions, AMPH and METH were equipotent at activating locomotor activity. The exceptions included when rats were presented with S+ on acute and drug challenge days, and in tests of cross-sensitization. There were no consistent differences in the magnitude of sensitization produced by AMPH or METH, and both drugs produced similar amounts of conditioned locomotion after a saline injection.Conclusions-We have found specific conditions where METH is more potent than AMPH, but this study and others that used higher doses of these drugs are not consistent with the generalized characterization of METH as a more potent psychostimulant.

Rationale: Repeated amphetamine (AMPH) exposure is known to cause long-term changes in AMPH-induced locomotor behavior (i.e., sensitization) that are associated with similarly long-lasting changes in brain function. It is not clear, however, if such exposure produces long-lasting changes in a cognitive behavior that, in humans, is hypothesized to contribute to addiction. Objectives:To examine whether repeated AMPH exposure induces both locomotor sensitization and alters impulsive choice in a delay-discounting task.Methods: Adult, male Sprague-Dawley rats (n = 29) were pre-treated with 3.0 mg/kg AMPH or saline every other day for 20 days, and were then trained to lever press for small, immediately delivered food reinforcement or larger reinforcements delivered after delays. We subsequently assessed the effects of acute AMPH (0.1-2.0 mg/kg) on delay-discounting. Lastly, we tested for longlasting effects of pre-treatment by giving an AMPH challenge (3.0 mg/kg) one week after the final delay-discounting session.Results: Repeated AMPH produced sensitization to the drug's stereotypy-inducing effects, but did not alter acquisition or baseline behavior in the delay-discounting task. Following acute AMPH, impulsive choice and other measures of delay-discounting were altered, but to a similar extent in both saline-and AMPH-pretreated groups. The AMPH challenge, given ∼3 months after the last pretreatment injection, revealed sensitization was still evident. Conclusions:Our results suggest that one behavioral consequence of repeated AMPH exposure -sensitization -does not overlap with another potential outcome -increased impulsivity. Furthermore, the neuroadaptations known to be associated with sensitization may be somewhat distinct from those that lead to changes in impulsive choice.