EFFECT OF NUCLEUS-ACCUMBENS DOPAMINE DEPLETION ON MOTIVATIONAL ASPECTS INVOLVED IN INITIATION OF COCAINE AND HEROIN SELF-ADMINISTRATION IN RATS

The involvement of mesolimbic dopamine (DA) systems in motivational as pects of drug-taking behavior during initiation of drug self-administr ation was investigated using a recently developed behavioral paradigm. In separate experiments animals were allowed to self-administer cocai ne or heroin (0.16 and 0.32 mg . kg(-1) per inf) during 5 consecutive daily 3-h sessions. During a 15-min period preceding the last four sel f-administration sessions lever-press behavior was measured in absence of the drug as an index of the motivational aspects involved in drug- taking behavior. The effect of 6-hydroxydopamine (6-OHDA) lesion of th e nucleus accumbens (NAG) on lever-press behavior before and during se lf-administration was measured. Destruction of DA terminals in the NAC did not affect initiation of heroin self-administration nor the lever -press behavior during the period preceding the self-administration se ssions. In cocaine animals 6-OHDA lesion of the NAC decreased the tota l intake of cocaine during the self-administration sessions and impair ed discriminative lever-responding for the drug, both during cocaine s elf-administration, and during preceding periods when no cocaine was a vailable. It is concluded that DAergic systems in the NAC might be inv olved in the reinforcement and/or motivational processes underlying co caine self-administration. The present findings, however, do not suppo rt the notion of a critical role of NAC DA in the motivational aspects of drug-taking behavior in general.