Diversity and connectivity of principal neurons in the lateral and basal nuclei of the mouse amygdala

The basolateral amygdala (BLA) is a cortical structure playing a role in various cognitive processes. In spite of many studies focusing on local information processing within the circuits of the BLA, the features of amygdalar principal neurons (PNs) remained elusive. Here, we combined neuroanatomical, electrophysiological and tracing techniques to determine the single-cell features, dendritic and axonal projections of PNs within the lateral (LA) and basal amygdala (BA). Using a mouse reporter line, we found that cholecystokinin (CCK) expression defined two groups of spatially segregated PNs both in the LA and BA. CCK+ PNs in the LA had small somata and short dendrites which matched to their passive and active membrane properties. CCK- PNs in the LA and all BA had similarly ramified dendrites and single-cell features with some differences. Importantly, the dendritic arbors of PNs restricted to the sub-nuclei defined by the CCK expression, which matches some of the extra-amygdalar inputs. Axonal arborization patterns of PNs within the BLA and surrounding areas showed correspondence to their soma location. For instance, BA PNs that projected to the medial prefrontal cortex or dorsomedial striatum were found in the medial part of the BA, revealing a significant overlap between the two neuronal populations. In contrast, those BA PNs that projected to this lateral part of the central nucleus located in the lateral region of the BA. Our results uncovered the diverse input and output properties of PNs in the LA and BA that help define the information flow within the BLA networks.