Effects of quinolinic acid-induced lesions of the nucleus accumbens core on inter-temporal choice: a quantitative analysis.
BACKGROUND
There is evidence that lesions of the nucleus accumbens core (AcbC) promote preference for smaller earlier reinforcers over larger delayed reinforcers in inter-temporal choice paradigms. It is not known whether this reflects an effect of the lesion on the rate of delay discounting, on sensitivity to reinforcer magnitude, or both.


OBJECTIVE
We examined the effect of AcbC lesions on inter-temporal choice using a quantitative method that allows effects on delay discounting to be distinguished from effects on sensitivity to reinforcer size.


METHODS
Sixteen rats received bilateral quinolinic acid-induced lesions of the AcbC; 14 received sham lesions. They were trained under a discrete-trials progressive delay schedule to press two levers (A and B) for a sucrose solution. Responses on A delivered 50 microl of the solution after a delay d(A); responses on B delivered 100 microl after d(B). d(B) increased across blocks of trials, while d(A) was manipulated across phases of the experiment. Indifference delay d(B(50)) (value of d(B) corresponding to 50% choice of B) was estimated in each phase, and linear indifference functions (d(B(50)) vs d(A)) derived.


RESULTS
d(B(50)) increased linearly with d(A) (r(2) > 0.95 in each group). The intercept of the indifference function was lower in the lesioned than the sham-lesioned group; slope did not differ between groups. The lesioned rats had extensive neuronal loss in the AcbC.


CONCLUSIONS
The results confirm that lesions of the AcbC promote preference for smaller, earlier reinforcers and suggest that this reflects an effect of the lesion on the rate of delay discounting.
Psychopharmacology Section, Division of Psychiatry, University of Nottingham, Room B109 Medical School, Queen's Medical Centre, Nottingham, UK.
G
G
Bezzina
T H C
TH
Cheung
K
K
Asgari
C L
CL
Hampson
S
S
Body
C M
CM
Bradshaw
E
E
Szabadi
J F W
JF
Deakin
I M
IM
Anderson
D000465:Algorithms; D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D002755:Choice Behavior / Q000187:drug effects*; D003216:Conditioning, Operant / Q000187:drug effects; D005260:Female; D007120:Immunochemistry; D008953:Models, Anatomic; D009419:Nerve Tissue Proteins / Q000032:analysis; D009687:Nuclear Proteins / Q000032:analysis; D009714:Nucleus Accumbens / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D011594:Psychometrics / Q000379:methods / Q000592:standards; D017378:Quinolinic Acid / Q000008:administration & dosage / Q000633:toxicity*; D051381:Rats; D017208:Rats, Wistar; D012055:Reinforcement Schedule; D012996:Solutions / Q000008:administration & dosage / Q000737:chemistry; D013238:Stereotaxic Techniques; D013395:Sucrose / Q000008:administration & dosage / Q000737:chemistry; D013997:Time Factors
D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D012996:Solutions; D013395:Sucrose; D017378:Quinolinic Acid