Changes in the effects of d-amphetamine on escape responding by its prior effects on punished responding.

Responses of squirrel monkeys adjusted the intensity of a continuous electric shock under two different schedules. In one schedule, responses decreased a shock intensity which otherwise was increased at a fixed rate (escape). In the other schedule, responses produced food pellets but also increased a shock intensity which otherwise decreased at a fixed rate (punishment). When animals were first studied under the escape schedule, d-amphetamine increased responding. Similarly, when animals had an intervening experience under the punishment schedule with no drugs administered, or when the drug was given but shock increments were tempoerarily eliminated during those drug sessions, d-amphetamine still increased subsequent escape responding. However, when animals under the punishment schedule were given d-amphetamine and shock increments occurred as usual during the drug session, the drug no longer increased either punished or subsequent escape responding. The effects of d-amphetamine on escape responding were completely different depending on the individual's prior drug experience.