Collateralization patterns of principal basolateral amygdala neurons delineate distinct output streams

The basolateral amygdala (BLA) projects to many brain regions through which it influences multiple functions. However, there is disagreement regarding the extent to which BLA axons collateralize. Using viral tracing, we found that distinct groups of BLA neurons send axon collaterals to different subsets of targets. A first group of BLA neurons projects to a hitherto underestimated combination of cortical and subcortical regions that regulate habitual or motivated behaviors, attention control, energy homeostasis, and olfactory processing. A second group of BLA neurons targets subcortical structures implicated in the genesis of defensive behaviors. By contrast, BLA neurons targeting cortical areas that support memory (hippocampus, rhinal cortices) collateralize sparingly. Overall, these results indicate that the BLA contains different clusters of neurons that contribute branching axons to distinct arrays of largely non-overlapping targets. These results impose a revision of how we conceptualize the BLA's coordination with, and influence over, its targets.