Effects of L-methamphetamine treatment on cocaine- and food-maintained behavior in rhesus monkeys
Monoamine releasers with prominent dopaminergic actions, e.g., d-methamphetamine (d-MA), significantly reduce cocaine use and craving in clinical and preclinical laboratory studies. However, D-MA and related drugs also display high abuse potential, which limits their acceptability as agonist replacement medications for the management of Cocaine Use Disorder.
The l-isomer of methamphetamine (l-MA), unlike d-MA, has preferential noradrenergic actions and is used medicinally with low, if any, abuse liability. The present study was conducted to determine whether l-MA could serve as an agonist replacement medication by both mimicking interoceptive effects of cocaine and decreasing intravenous (IV) cocaine self-administration.
Separate groups (N = 4-5) of rhesus monkeys were studied to determine whether l-MA could (1) substitute for cocaine in subjects that discriminated intramuscular (IM) cocaine (0.4 mg/kg) from saline and (2) decrease IV cocaine self-administration under a second-order FR2(VR16:S) schedule of reinforcement.
l-MA, like d-MA but with approximately 5-fold lesser potency, substituted for cocaine in drug discrimination experiments in a dose-dependent manner. In IV self-administration studies, 5-10-day treatments with continuously infused l-MA (0.032-0.32 mg/kg/h, IV) dose-dependently decreased cocaine-maintained responding; the highest dosage reduced cocaine intake to levels of saline self-administration without appreciable effects on food-maintained responding.
These results indicate that l-MA both shares discriminative stimulus effects with cocaine and reduces cocaine self-administration in a behaviorally selective manner. l-MA and other compounds with a similar pharmacological profile deserve further evaluation for the management of Cocaine Use Disorder.