The effect of amphetamine on locomotion depends on the motor device utilized: The open field vs. the running wheel

The effect of amphetamine on the level of locomotion exhibited on two diffe rent motor devices was examined in the Golden hamster. Increasing concentra tions of the psychostimulant from 4 to 10 mg/kg significantly enhanced Loco motor activity in hamsters exposed to an open field. A further increase to 25 mg/kg inhibited ambulatory activity to levels below the control baseline , while augmenting the occurrence of stereotypic behaviors. The activating effect of amphetamine on ambulatory activity was observed regardless of the time of testing (day or night) or lighting condition, with no apparent mod ulation by the circadian system. On the other hand, home-cage wheel-running activity was maximally inhibited by 10 mg/kg amphetamine, whereas a smalle r dosage (1.5 mg/kg) had no effect over the wheel-running activity baseline of saline controls. Although both the running wheel and the open field qua ntify locomotion, the dissociation obtained shows that they measure differe nt components of it. The results are interpreted within Lyon and Randrup's hypothesis on the actions of amphetamine (16). (C) 2000 Elsevier Science In c.