Morphological and electrophysiological diversity and connectivity of principal neurons in the lateral and basal nuclei of the mouse amygdala

The basolateral amygdala is a cortical structure involved in various cognitive functions. Despite numerous studies on amygdala operation, the properties of its excitatory principal neurons (PNs) are not fully characterized. Here, we combined neuroanatomical, electrophysiological, and tracing methods to analyze the single-cell features and morphological characteristics of PNs in the lateral (LA) and basal amygdala (BA). Using a mouse reporter line, we found that cholecystokinin (CCK) promoter-driven DsRed expression defines two distinct PN populations. PNs in the DsRed-positive area of the LA had small somata and short dendrites, consistent with their electrophysiological profiles. PNs in the DsRed-negative area of the LA and all PNs in the BA showed similarly ramified dendrites and single-cell features. Importantly, PN dendritic arbors were confined to DsRed-defined subnuclei, which correlated with distinct extra-amygdalar inputs, indicating input specificity. Axonal projections also corresponded with soma location; for example, BA PNs projecting to the medial prefrontal cortex - but not to the lateral nucleus of the central amygdala (CEAl) - were found in the DsRed-positive subnucleus, whereas those projecting to the CEAl were located in the DsRed-negative subnucleus. Our findings reveal that the basolateral amygdala contains distinct subnuclei with specific input-output patterns, enabling flexible information processing necessary for the diverse amygdala functions.