Effects of chronic administration of (+)-amphetamine on maze performance of the rat.

1. The influence of (+)-amphetamine, given 1 min after each training session, on the performance of 124 rats in a Lashley III maze was measured every 48 hr.2. The first three injections of the drug significantly improved the learning ability of naive rats.3. With prolonged treatment, (+)-amphetamine strongly impaired the maze performance of these rats.4. The chronic administration of (+)-amphetamine to previously trained rats produced the same adverse effect.5. Amylobarbitone sodium given to previously trained rats 30 min before the training sessions completely blocked the adverse effect of (+)-amphetamine.6. (+)-Amphetamine did not produce impairment of performance when given chronically 30 min before training sessions, to previously trained rats.