Organizational principles of amygdalar input-output neuronal circuits

The amygdala, one of the most studied brain structures, integrates brain-wide heterogeneous inputs and governs multidimensional outputs to control diverse behaviors central to survival, yet how amygdalar input-output neuronal circuits are organized remains unclear. Using a simplified cell-type- and projection-specific retrograde transsynaptic tracing technique, we scrutinized brain-wide afferent inputs of four major output neuronal groups in the amygdalar basolateral complex (BLA) that project to the bed nucleus of the stria terminals (BNST), ventral hippocampus (vHPC), medial prefrontal cortex (mPFC) and nucleus accumbens (NAc), respectively. Brain-wide input-output quantitative analysis unveils that BLA efferent neurons receive a diverse array of afferents with varied input weights and predominant contextual representation. Notably, the afferents received by BNST-, vHPC-, mPFC- and NAc-projecting BLA neurons exhibit virtually identical origins and input weights. These results indicate that the organization of amygdalar BLA input-output neuronal circuits follows the input-dependent and output-independent principles, ideal for integrating brain-wide diverse afferent stimuli to control parallel efferent actions. The data provide the objective basis for improving the virtual reality exposure therapy for anxiety disorders and validate the simplified cell-type- and projection-specific retrograde transsynaptic tracing method.

Cellular Physiology of the Basolateral Complex of the Amygdala and Its Modulation by Stress

Fear is a critical emotional response that allows an organism to safely navigate through dangerous environments. The neural systems underlying the fear response have been well characterized, and include the amygdala, hippocampus, prefrontal cortex, bed nucleus of stria terminalis, nucleus accumbens, and others. While normally these brain regions coordinate to produce an appropriate fear response, the fear network in humans can become dysregulated after a traumatic event. The resulting phenotype of hyperarousal, avoidance, and re-experiencing of fear known as post-traumatic stress disorder (PTSD) is a growing problem in the United States. This chapter focuses on the role of the basolateral complex (BLC) of the amygdala, which has been implicated in the neuropathology of PTSD, particularly the hyperarousal, fear generalization, and fear extinction deficits characteristic of the disorder, as well as aspects of the microcircuitry, network connectivity, and neuromodulation of the BLC that may be involved in the pathophysiology of PTSD.