Reinforcing effects of smoked methamphetamine in rhesus monkeys.
BACKGROUND
The occurrence of methamphetamine (METH) use by the smoking route is increasing. A nonhuman primate model for examining the reinforcing effects of smoked METH would be valuable for testing potential interventions for treating METH abuse disorders.


OBJECTIVE
The purpose of the present study was to examine the reinforcing effects of smoked METH in monkeys.


METHODS
Four rhesus monkeys were trained to smoke cocaine (COC) under a chain fixed-ratio (FR) 64 lever press, FR 5 inhalation schedule of reinforcement. Upon observing stable levels of self-administration, METH was substituted for COC and a dose-response function for METH (0.08-0.8 mg/kg) was determined. Subsequently, the number of deliveries of COC (1 mg/kg), and 0.2 and 0.8 mg/kg METH were examined across increasing response requirements.


RESULTS
METH was dose-dependently self-administered. Higher doses of METH (0.2, 0.4, and 0.8 mg/kg) produced asymptotic levels of responding that were slightly lower than those obtained with 1 mg/kg COC. Numbers of deliveries of COC and METH decreased as response requirement increased. METH, however, maintained fewer deliveries than 1 mg/kg COC at most response requirements.


CONCLUSIONS
METH is readily self-administered by smoking in rhesus monkeys when substituted for COC. METH may have a lower reinforcing strength than COC, but further research is needed to fully characterize its relative reinforcing strength.
Newman
Jennifer L
JL
Department of Psychiatry, University of Minnesota Medical School, MMC 392, Minneapolis, MN 55455, USA. newma210@umn.edu
Carroll
Marilyn E
ME
D019969:Amphetamine-Related Disorders / Q000523:psychology*; D000818:Animals; D003042:Cocaine / Q000008:administration & dosage; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D008253:Macaca mulatta; D008297:Male; D008694:Methamphetamine / Q000008:administration & dosage*; D012054:Reinforcement, Psychology; D012646:Self Administration; D012907:Smoking
D008694:Methamphetamine; D003042:Cocaine