Methamphetamine, physostigmine, atropine and mecamylamine: effects on force lever performance

Area of Science:

• Neuroscience
• Pharmacology
• Primate Behavior

Background:

• Methamphetamine (MA) is a stimulant with known effects on motor control.
• Understanding drug tolerance and its neurochemical underpinnings is crucial for addiction research.
• Cholinergic systems interact with dopaminergic pathways, influencing motor function.

Purpose of the Study:

• To determine dose-response functions of d-methamphetamine (MA), physostigmine, atropine, and mecamylamine on rhesus monkey motor control.
• To investigate the effects of a repeated high-dose MA regimen on the sensitivity to these drugs.
• To measure changes in brain monoamine concentrations following the MA treatment regimen.

Main Methods:

• Three rhesus monkeys were trained on a force lever task measuring motor control.
• Dose-response curves for MA, physostigmine, atropine, and mecamylamine were established.
• Monkeys received a repeated high-dose MA regimen, after which drug effects were re-evaluated.
• Post-behavioral assessment, brain monoamine levels (dopamine, serotonin) were quantified.

Main Results:

• All four drugs exhibited differential effects on force lever performance indices.
• Following the MA regimen, monkeys showed reduced sensitivity to MA's effects on motor control.
• Sensitivity to physostigmine, atropine, and mecamylamine remained unchanged after MA treatment.
• MA-treated monkeys exhibited decreased brain dopamine and serotonin concentrations.

Conclusions:

• Repeated high-dose MA induces specific tolerance to its own motor control effects in rhesus monkeys.
• This MA-induced tolerance does not extend to cholinergic agents, suggesting pathway specificity.
• The observed decrease in brain dopamine and serotonin levels may underlie MA tolerance and neurotoxicity.