Effect of quinolinic acid-induced lesions of the nucleus accumbens core on performance on a progressive ratio schedule of reinforcement: implications for inter-temporal choice.
BACKGROUND
The nucleus accumbens core (AcbC) is believed to contribute to the control of operant behaviour by reinforcers. Recent evidence suggests that it is not crucial for determining the incentive value of immediately available reinforcers, but is important for maintaining the values of delayed reinforcers.


OBJECTIVE
This study aims to examine the effect of AcbC lesions on performance on a progressive-ratio schedule using a quantitative model that dissociates effects of interventions on motor and motivational processes (Killeen 1994 Mathematical principles of reinforcement. Behav Brain Sci 17:105-172).


METHODS
Rats with bilateral quinolinic acid-induced lesions of the AcbC (n = 15) or sham lesions (n = 14) were trained to lever-press for food-pellet reinforcers under a progressive-ratio schedule. In Phase 1 (90 sessions) the reinforcer was one pellet; in Phase 2 (30 sessions), it was two pellets; in Phase 3, (30 sessions) it was one pellet.


RESULTS
The performance of both groups conformed to the model of progressive-ratio performance (group mean data: r2 > 0.92). The motor parameter, delta, was significantly higher in the AcbC-lesioned than the sham-lesioned group, reflecting lower overall response rates in the lesioned group. The motivational parameter, a, was sensitive to changes in reinforcer size, but did not differ significantly between the two groups. The AcbC-lesioned group showed longer post-reinforcement pauses and lower running response rates than the sham-lesioned group.


CONCLUSIONS
The results suggest that destruction of the AcbC impairs response capacity but does not alter the efficacy of food reinforcers. The results are consistent with recent findings that AcbC lesions do not alter sensitivity to reinforcer size in inter-temporal choice schedules.
Bezzina
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Psychopharmacology Section, Division of Psychiatry, University of Nottingham, Room B109, Medical School, Queen's Medical Centre, Nottingham NG7 2UH, UK.
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Cheung
T H C
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Hampson
C L
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Deakin
J F W
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Anderson
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Szabadi
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Bradshaw
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D000818:Animals; D001835:Body Weight / Q000502:physiology; D002755:Choice Behavior / Q000187:drug effects*; D003216:Conditioning, Operant / Q000187:drug effects*; D003463:Cues; D003627:Data Interpretation, Statistical; D005260:Female; D005508:Food Deprivation; D007150:Immunohistochemistry; D009714:Nucleus Accumbens / Q000187:drug effects*; D011597:Psychomotor Performance / Q000187:drug effects*; D017378:Quinolinic Acid / Q000633:toxicity*; D051381:Rats; D017208:Rats, Wistar; D012055:Reinforcement Schedule; D012054:Reinforcement, Psychology; D012420:Running / Q000523:psychology
D017378:Quinolinic Acid