The effects of nucleus accumbens core and shell lesions on intravenous heroin self-administration and the acquisition of drug-seeking behaviour under a second-order schedule of heroin reinforcement.
BACKGROUND
Evidence has implicated the nucleus accumbens (NAcc) in drug-seeking and -taking behaviour. However, the importance of the "core" and "shell" subdivisions of the NAcc in heroin-seeking and -taking behaviour remains unclear.


OBJECTIVE
To investigate the function of the NAcc core and shell in heroin self-administration and heroin-seeking behaviour.


METHODS
Male rats were trained to self-administer heroin (0.12 mg/kg per infusion) under a continuous reinforcement (CRF) schedule. After responding stabilised, rats were given excitotoxic (or sham) lesions of either the NAcc core or shell and after recovery were assessed for their retention of heroin self-administration under CRF. At this point a second-order schedule of reinforcement was introduced, commencing at FR10 (FR1:S) and terminating at FR10 (FR10:S), in which ten lever presses resulted in presentation of the heroin-associated CS+, and completion of ten such units resulted in drug infusion.


RESULTS
Within 7 days, all groups re-acquired responding for heroin under CRF at rates similar to their pre-lesion performance. However, rats with lesions of the NAcc core, but not shell, were severely impaired in the acquisition of heroin-seeking behaviour.


CONCLUSIONS
These results indicate an important role for the core of the NAcc in the acquisition of heroin-seeking behaviour under the control of drug-associated stimuli.
Department of Experimental Psychology, University of Cambridge, UK.
D M
DM
Hutcheson
J A
JA
Parkinson
T W
TW
Robbins
B J
BJ
Everitt
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D003216:Conditioning, Operant; D004305:Dose-Response Relationship, Drug; D018690:Excitatory Amino Acid Agonists / Q000633:toxicity; D006556:Heroin Dependence / Q000523:psychology*; D007051:Ibotenic Acid / Q000633:toxicity; D008297:Male; D020258:Neurotoxicity Syndromes / Q000473:pathology / Q000523:psychology*; D009498:Neurotoxins / Q000633:toxicity; D009714:Nucleus Accumbens / Q000187:drug effects / Q000473:pathology / Q000502:physiology*; D017378:Quinolinic Acid / Q000633:toxicity; D051381:Rats; D012055:Reinforcement Schedule; D012646:Self Administration; D015819:Substance Abuse, Intravenous / Q000523:psychology*
D018690:Excitatory Amino Acid Agonists; D009498:Neurotoxins; D007051:Ibotenic Acid; D017378:Quinolinic Acid