The effects of dopaminergic agents on the locomotor activity of rats after high doses of methylamphetamine.

Treatment of rats with 100 mg/kg/day of methylamphetamine for four days produced long lasting (16 week) depletions of central nervous system levels of dopamine but not of norepinephrine. This methylamphetamine treatment also attenuated the ability of methylamphetamine and apomorphine to produce increases in locomotor activity without shifting the dose-response curve to the right or left. These rats underwent significant decreases in activity after lower doses of haloperidol while the response to L-Dopa was virtually unchanged.