title: L-methamphetamine and selective MAO inhibitors decrease morphine-reinforced and non-reinforced behavior in rats; Insights towards selegiline's mechanism of action.
abstract: Selegiline is an inhibitor of type B monoamine oxidase (MAO) with psychostimulant effects that can decrease morphine-reinforced and non-reinforced responding. The present study was undertaken to compare the effects of MAO inhibition and treatment with L-methamphetamine, the major psychostimulant metabolite of selegiline, on these behaviors. After rats acquired a stable pattern of morphine self-administration under a progressive ratio schedule, chronic treatment was initiated with vehicle, L-methamphetamine, clorgyline (a selective inhibitor of MAO-A), or rasagiline (a selective inhibitor of MAO-B); with both MAO inhibitors administered at a dose selective for one MAO isoform and a higher dose that inhibited both isoforms. Rats were evaluated for up to four cycles of opiate dependence maintained by morphine self-administration and withdrawal during which extinction responding was recorded. Most behavioral measures (92.4%) did not differ in animals evaluated during an initial and subsequent cycles of dependence and withdrawal. All active treatments attenuated non-reinforced responding during extinction. Morphine reinforcement was also decreased by each of the three active treatments, but greater and more prolonged effects were observed following inhibition of MAO-B with rasagiline. Responding during either cue- or morphine-induced reinstatement was attenuated by either clorgyline or rasagiline administered at nonselective doses, but not by either compound administered at selective dose levels. Treatment with L-methamphetamine did not produce significant effects on cue-induced reinstatement, but decreased non-reinforced responding during morphine-induced reinstatement. These findings indicate that morphine reinforcement and different non-reinforced behaviors differ greatly in their susceptibility to modification by psychostimulant treatment or MAO inhibition.
authors.affiliation: Substance Abuse Research Laboratory, Kansas City Veterans Affairs Medical Center, 4801 Linwood Boulevard, Kansas City, MO 64128, USA.
authors.forename: Shuangteng
authors.initials: S
authors.lastname: He
authors.forename: Kenneth
authors.initials: K
authors.lastname: Grasing
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D001835:Body Weight / Q000187:drug effects; D000697:Central Nervous System Stimulants / Q000008:administration & dosage / Q000494:pharmacology*; D003010:Clorgyline / Q000008:administration & dosage / Q000494:pharmacology; D003216:Conditioning, Operant; D005108:Extinction, Psychological; D007189:Indans / Q000008:administration & dosage / Q000494:pharmacology; D008297:Male; D008694:Methamphetamine / Q000008:administration & dosage / Q000494:pharmacology*; D008996:Monoamine Oxidase Inhibitors / Q000008:administration & dosage / Q000627:therapeutic use*; D009020:Morphine / Q000008:administration & dosage / Q000009:adverse effects / Q000494:pharmacology*; D009021:Morphine Dependence / Q000523:psychology*; D051381:Rats; D017208:Rats, Wistar; D012054:Reinforcement, Psychology; D012642:Selegiline / Q000008:administration & dosage / Q000494:pharmacology*; D012646:Self Administration; D013375:Substance Withdrawal Syndrome / Q000523:psychology
chemical_list: D000697:Central Nervous System Stimulants; D007189:Indans; D008996:Monoamine Oxidase Inhibitors; C031967:rasagiline; D012642:Selegiline; D008694:Methamphetamine; D009020:Morphine; D003010:Clorgyline