Interactions between amygdala central nucleus and the ventral tegmental area in the acquisition of conditioned cue-directed behavior in rats

Abstract

Rats orient to and approach localizable visual cues paired with food delivery. Previous studies from this laboratory show that the acquisition and expression of these learned cue-directed responses depend on integrity of a system including the central nucleus of the amygdala (CeA), the substantia nigra pars compacta (SNc) and the dorsolateral striatum (DLS). Other investigators have suggested that cue-directed behaviors may also depend on interaction between CeA and the ventral striatum, perhaps via CeA projections to the ventral tegmental area (VTA). In Experiment 1, we examined the effects of unilateral lesions of CeA and/or VTA on rats' acquisition of conditioned responses to visual cues paired with food. Contrary to the results of previous studies that examined interactions of CeA with either SNc or DLS, rats with contralateral disconnection lesions of CeA and VTA were unimpaired in their acquisition of cue-directed responses. By contrast, rats with lesions of both structures in the same hemisphere failed to learn cue-directed responses, but were normal in their acquisition of conditioned responses directed to the food cup. In Experiment 2, we attempted to characterize the influence of VTA on CeA by examining FOS induction in CeA by a visual cue for food in rats with unilateral lesions of VTA. The results suggested an excitatory influence of VTA on CeA in the presence of food cues. Implications of these results for brain circuits involved in learned orienting and incentive motivation are discussed.