Circuit organization and transcriptomic heterogeneity of sympathetic circuits innervating cranial structures.

The superior cervical ganglion (SCG) innervates multiple effector organs within cranial tissues and elicits responses including pupil dilation, piloerection, vasoconstriction, and inhibition of salivation. Coordinated activation of these targets is associated with the display of different emotions; however, the underlying circuit organization and cellular heterogeneity of SCG neurons remain unclear. Here, we combined neuronal tracing with single-cell and spatial transcriptomics to characterize the SCG circuitry and heterogeneity. We found that each SCG neuron innervates a single effector organ. SCG subtypes defined by their projection (P) targets form two major compartments within the ganglia, but individual P-types were intermingled. Mature SCG transcriptomic (T) types emerge postnatally and exhibit rostra-caudal biases. While some T-types were enriched in SCG populations with specific axon projections, they did not show a strict one-to-one correspondence with P-types. These results suggest that individual sympathetic cranial effectors mediating facial emotions are controlled combinatorially by multiple transcriptomic SCG types.