Opposing Influence of Basolateral Amygdala and Footshock Stimulation on Neurons of the Central Amygdala

Abstract

The basolateral complex (BLA) and the central nucleus of the amygdala (CeA) are believed to mediate the expression of affective responses. After affective learning, conditioned stimulus-related information is thought to be conveyed from the BLA to the CeA; the medial CeA (Cem), in turn, projects to hypothalamic and brainstem structures involved with induction of affective responses. Although the conditioned stimulus and unconditioned stimulus both evoke affective responses, the precise response often differs. It is unknown whether this difference is represented by distinct activity patterns of single Cem neurons. Furthermore, the nature of the interaction between the BLA and Cem is unknown. Using in vivo extracellular and intracellular recordings, we examined how the BLA affects the Cem and compared this with effects induced by footshock (unconditioned stimulus) in the same neurons. Our results demonstrate that, contrary to conventional views, BLA stimulation primarily inhibits Cem neurons by a polysynaptic circuit, and show that single Cem neurons respond to both BLA input and footshock in an opposite manner. These results demonstrate the predominantly inhibitory nature of the BLA-Cem interaction. These data further demonstrate the distinct cellular events that might lead to differential modulation of conditioned and unconditioned affective responses.