Performance enhancement effects of d-amphetamine, methylphenidate, pipradrol and phenindamine in rats

A multiple behavioral schedule with food reinforcement was designed to measure the drug-induced performance enhancement and non-effective activity in rats. The schedule, 20 min in duration, had CRF components in the 33 trials and extinction components in the inter-trial periods. During each trial, food reinforcement was present in the limited period (8 sec each) which was preceded by a discriminative stimulus (1 sec, either a light or a footshock). The rats generated a high rate of lever pressing during the limited period and a low rate of lever pressing during the inter-trial period. The drugs studied were d-amphetamine, methylphenidate, pipradrol and phenindamine. At low dosages, these drugs increased further the high rate of lever pressing. This was considered to be the performance enhancement effect. At higher doses, the drugs increased the low rate of lever pressing, decreased the high rate of lever pressing, and decreased responding of the rats to the discriminative stimulus. This latter pattern was considered to be the non-effective activity caused by the drugs. As expected, d-amphetamine was the most potent. Minor differences in drug effects were seen between the group of rats having light and that group having footshock as discriminative stimulus.