The ventral pallidum plays a role in mediating cocaine and heroin self-administration in the rat.
The hypothesis that the ventral pallidum is an important site mediating psychomotor stimulant and opiate reinforcement was tested in rats trained to self-administer i.v. cocaine or heroin. Ibotenic acid lesions of the ventral pallidum produced significant decreases in cocaine and heroin self-administration behavior maintained on a fixed-ratio 5 schedule of reinforcement, suggesting an attenuation of the reinforcing value of cocaine and heroin. On a progressive-ratio schedule, ventral pallidal lesions produced significant decreases in the highest ratio obtained in rats self-administering cocaine. Similar results were observed with heroin in a progressive-ratio procedure modified to produce higher levels of responding; lesions of the ventral pallidum produced a significant decrease in the highest ratio obtained. Further, the i.v. co-administration of naloxone and heroin produced a decrease in progressive-ratio responding relative to heroin alone using the modified progressive-ratio schedule. These results suggest that the ventral pallidum is an important site mediating the reinforcing effects of cocaine and heroin and that the nucleus accumbens-ventral pallidum circuit may be a common pathway for both stimulant and opiate reinforcement.
Hubner
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CB
Division of Preclinical Neuroscience and Endocrinology, Research Institute of Scripps Clinic, La Jolla, CA 92037.
Koob
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GF
D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D003042:Cocaine / Q000008:administration & dosage*; D005917:Globus Pallidus / Q000187:drug effects / Q000502:physiology*; D003932:Heroin / Q000008:administration & dosage*; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D012055:Reinforcement Schedule; D012646:Self Administration
D003932:Heroin; D003042:Cocaine