Functional interaction between the basolateral amygdala and the nucleus accumbens underlies incentive motivation for food reward on a fixed ratio schedule.

ABSTRACT

The ability for incentive properties of reward stimuli to maintain motivated behavior in the absence of the rewards themselves may be reliant in part on a glutamatergic projection from the basolateral (BLA) amygdala to the nucleus accumbens septi (NAS). The present work examined this idea in regard to food reward. In the first part of this study, lever pressing by rats on a fixed ratio 16 (FR16) schedule of food reinforcement was suppressed in a dose-dependent manner following bilateral infusion of the GABA(A) agonist muscimol to the BLA. Consumption of food when freely available was unaffected by the highest dose of muscimol, suggesting no change in the primary reward value of the food. Bilateral infusion of the broad-spectrum dopamine (DA) receptor antagonist flupenthixol to the NAS also resulted in a significant decrease in FR16 performance. As with the amygdala, consumption of freely available food was not affected by flupenthixol injections into the NAS. When unilateral injection of flupenthixol to the NAS was combined with contralateral injection of muscimol to the BLA, FR16 performance was suppressed. No significant change in lever press performance was observed following unilateral NAS injection of flupenthixol combined with ipsilateral injection of muscimol to the BLA. The results of this study support the idea that a functional connection between the BLA and NAS transmits incentive information necessary for the maintenance of responding in the absence of primary reward.