Effects of repeated methamphetamine administration on methamphetamine self-administration in rhesus monkeys.

The effects of prolonged exposure to high doses of stimulants on stimulant self-administration in rhesus monkeys have not been established. In the present experiment, rates of methamphetamine self-administration as well as the effects of methamphetamine on food-maintained responding were determined before and after a regimen of repeated methamphetamine injections. Increases in self-administration of some doses of methamphetamine as well as tolerance to the rate-decreasing effects of the drug on food-maintained responding were observed following the repeated injection regimen. The results suggest that while tolerance may develop to the rate-decreasing effects of the drug, there may be an increased sensitivity to its reinforcing properties. In addition, since this injection regimen has been shown in previous studies to deplete central monoamines, especially dopamine, the results suggest a role for these monoamines in these behavioral effects of methamphetamine.