Basolateral Amygdala Input to the Claustrum: Topology, Excitatory Synapse Properties and Cellular Targets

Although the claustrum (CLA) has been increasingly implicated in salience and attentional processing, its relationship with the basolateral amygdala (BLA)—a key structure for emotional valence—remains poorly defined. Here, we used viral tracing, optogenetics, and brain slice electrophysiology to characterize the spatial organization and function of BLA–CLA circuitry. We found a clear anatomical compartmentalization of axonal projections between the BLA and CLA within the ring-like outer shell of the CLA, with little axonal labeling in the CLA core. Given this anatomical segregation, it was surprising that optogenetic photostimulation of BLA axons produced comparable excitatory responses in neurons in both the CLA core and shell. Pharmacological experiments indicated that BLA axons make monosynaptic contact with both shell and core neurons, with the latter likely doing so via their distal dendrites that extend into the shell. When CLA neurons were stratified according to their projection targets, BLA axons overlapped more with CLA neurons projecting to the motor cortex than those projecting to the retrosplenial cortex. However, synaptic responses to BLA input were similar in CLA neurons projecting to both cortical targets. Our results provide the first functional characterization of a BLA input pathway that potentially carries valence-related signals to the CLA. Because the excitatory synaptic responses produced in CLA neurons by BLA input were small and subthreshold for action potential generation, our results also argue that the BLA input contributes to a broader convergence of excitatory inputs instead of being a primary driver of CLA activity.