Sources of variation in locomotor activity and stereotypy in rats treated with d-amphetamine.

Rats injected with doses of d-amphetamine 0--5.0 mg/kg were observed continuously in either an enclosed Y-maze or on an elevated Y-shaped platform. Patterns of increased walking and stereotypy were unaffected by the type of apparatus, but rearing remained totally suppressed at all dose levels on the elevated platform. In the second experiment, groups of rats where given single short tests in the enclosed Y-maze, which was novel to them. The stimulant actions of d-amphetamine on locomotion were obscured by high baseline levels of motor activity induced by the novel environment. Continuous measurements of habituated rats may provide a more sensitive means of evaluating stimulant actions of drugs in screening tests. The observed changes in patterns of onset and offset of increased locomotion and of stereotypy were consistent with the view that these types of behaviour are, to some extent, independently, mediated.