Methamphetamine effects on responding under a multiple schedule of shock presentation

Abstract

Squirrel monkeys responded under a multiple 3-min variable-interval (VI) 10-response fixed-ratio (FR) schedule of response-dependent electric shock presentation. Methamphetamine (0.01-0.17 mg/kg) produced dose-dependent increases in relatively low rates of responding whether these occurred during the FR or the VI component of the schedule. In the one monkey with a relatively high control rate of responding during the VI component, methamphetamine only produced decreases in responding. Responding during the FR component was increased by methamphetamine, even in the monkey whose responding appeared to be suppressed during this component. Previous experiments have shown only further decreases after amphetamines in responding suppressed by response-dependent shock. The present experiments indicate that, in addition to the frequency and intensity of the electric shock and to the schedule maintaining the reference behavior, the nature of the event maintaining the reference behavior can be important in determining the effects of amphetamines. The effects of methamphetamine depend not only on the intensive and temporal characteristics of the ongoing schedule-controlled behavior itself, but also on the past and present context in which the behavior occurs.