Neurotransmitter turnover in rat striatum is correlated with morphine self-administration

Drugs of abuse probably exert their reinforcing effects through 'reward' pathways in the central nervous system (CNS). Neuronal systems mediating opiate reinforcement have been investigated using pharmacological and electrolytic lesion procedures. Drugs that interfere with catecholaminergic and cholinergic neuronal activity decrease intravenous (i.v.) morphine self-administration in monkeys and rats. Electrolytic lesion procedures in rats have demonstrated that the medial forebrain bundle and caudate nucleus are important in maintaining i.v. morphine self-administration. We have now carried out a direct investigation of striatal (caudate nucleus, putamen and globus pallidus) neuronal systems. We show here that striatal catecholaminergic systems are important in mediating opiate reinforcement, and present direct evidence for the involvement of neurotransmitter systems in morphine reward.