title: Evidence that separate neural circuits in the nucleus accumbens encode cocaine versus "natural" (water and food) reward.
abstract: Electrophysiological recording procedures were used to examine nucleus accumbens (Acb) cell firing in rats trained to press a lever on a multiple schedule [ fixed ratio (FR)1, FR1] for either two "natural" reinforcers (food and water), or a natural reinforcer and intravenous self-administration of cocaine. Of 180 cells recorded during water and food reinforcement (n = 13 rats), 77 neurons were classified as phasically active, exhibiting one of three well-defined types of patterned discharges relative to the reinforced-response (Carelli and Deadwyler, 1994). Of the 77 phasic cells, the majority (68%) showed similar types of patterned discharges across the two natural reinforcer conditions. In contrast, of 127 neurons recorded during water and cocaine reinforcement (n = 8 rats), only 5 of 60 phasically active cells (8%) exhibited similar types of patterned discharges relative to water- and cocaine-reinforced responding. The remaining 55 phasic cells (92%) displayed patterned discharges relative to the cocaine-reinforced response (n = 26 cells), or relative to the water-reinforced response (n = 29 cells), but not both. For some rats (n = 3), food was substituted for water in the task. Again, the majority of phasic neurons (13 of 14 cells, 93%) exhibited nonoverlapping firing patterns across the drug and natural reinforcer conditions. These findings indicate that in the well-trained animal, cocaine activates a neural circuit in the Acb that is largely separate from the circuit that processes information about food and water reward.
authors.affiliation: Department of Psychology, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3270, USA. rcarelli@unc.edu
authors.forename: R M
authors.initials: RM
authors.lastname: Carelli
authors.forename: S G
authors.initials: SG
authors.lastname: Ijames
authors.forename: A J
authors.initials: AJ
authors.lastname: Crumling
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects / Q000502:physiology; D003042:Cocaine / Q000494:pharmacology*; D003216:Conditioning, Operant / Q000187:drug effects / Q000502:physiology; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology*; D004567:Electrodes, Implanted; D004594:Electrophysiology; D005502:Food; D007275:Injections, Intravenous; D008297:Male; D009415:Nerve Net / Q000502:physiology*; D009474:Neurons / Q000187:drug effects; D009714:Nucleus Accumbens / Q000166:cytology / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012201:Reward; D014867:Water
chemical_list: D018765:Dopamine Uptake Inhibitors; D014867:Water; D003042:Cocaine