Effects of Amygdala Inactivation on Affective Processing by the Nucleus Accumbens

Inappropriate affect is a major feature of many psychological disorders. Recent progress in the field of affective neuroscience has led to a basic understanding of the brain regions involved in emotional processing. However, this information remains incomplete as we have yet to directly link affective states to specific patterns of brain activity. One area implicated in affective processing is the nucleus accumbens (NAc). Recent studies have shown that the NAc encodes both rewarding and aversive stimuli, and does so by decreasing or increasing its overall activity, respectively. Furthermore, recent studies in our lab have shown that NAc signaling is modified to reflect changes in the affective value of stimuli due to learned associations or changes in motivational state. The NAc serves an important role in translating affective signals into appropriate behavioral action. Thus, signals from other regions could provide essential affective information which influence how NAc neurons respond to stimuli. One candidate source of these signals is the basolateral amygdala (BLA), which sends a glutamatergic projection to the NAc and is thought to link sensory properties of stimuli with affective significance. By inactivating the BLA while monitoring activity in the NAc we can determine the contribution of the BLA to affective processing in the NAc.;In order to accomplish this neural activity was recorded in the NAc of rats exposed to taste stimuli under BLA inactivation. This procedure was used to examine the role of the BLA in NAc encoding of innately rewarding (sucrose) and aversive (quinine) taste stimuli. The role of the central nucleus of the amygdala (CeA) in NAc encoding of taste stimuli was also investigated. This structure receives taste information directly from brainstem regions involved in taste processing and borders the BLA. Thirdly, to test effects of general inactivation of NAc efferents, the ventral subiculum of the hippocampus (Vsub), which also projects directly to the NAc, was inactivated while rats were exposed to rewarding and aversive taste stimuli.