The locomotor effects of (+)-amphetamine were examined in two groups of rats placed in chambers of different sizes. 2. Prior to drug exposure, rats in large chambers were more active, as measured on a rating scale. 3. Under amphetamine, ratings discriminated the 2.5 mg/kg dose from both saline and 0.25 mg/kg without observed differences between the latter two. Scores recorded automatically in the large chambers showed enhanced horizontal activity with both doses, although they did not differ amongst themselves. 4. Methodological variables, including the size of apparatus and recording technique may influence observed effects of amphetamine, and suggest these variables be taken into account when studying drug effects.
