Opioid-reinforced operant behavior: Selective suppression by alpha-methyl-para-tyrosine.

Conducted 4 experiments using a total of 24 Charles River male albino rats. Morphine-addicted Ss performed operant responses for opioid or milk rewards. When Ss were then denied access to opioids, abstinence symptoms developed. Responding under extinction conditions 2 wks after opioid withdrawal provided a measure of the "relapse" tendency. Systemic administration of alpha-methyl-para-tyrosine, an inhibitor of catecholamine synthesis, suppressed these responses if they had been reinforced by an opioid but not if they had been established with milk reinforcement. This indicates that the integrity of the catecholamine systems is vital for relapse to occur. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)