Intrinsic neuronal network organization of a mammalian peripheral nervous system.

The vertebrate nervous system is traditionally parceled topographically into central and peripheral divisions. The peripheral nervous system (PNS) in turn is commonly viewed functionally as a set of nerves and ganglia transmitting input and output signals between the central nervous system (CNS) and other bodily systems to regulate physiology and behavior. Here, we collate and analyze neuroanatomical data on putative directed and weighted axonal connections between peripheral ganglia in a mammal (rat). The resulting network reveals a sparse but broad intra-PNS neuronal architecture with over 100 connections among 52 of the 84 sensory and autonomic ganglia identified. Local network differentiation of the associated 52×52 connection matrix (connectome) was examined with cluster analysis. It identified 22 modules (subsystems or subnetworks) within a six-level nested hierarchy, including seven first-order modules and 14 end modules, spatially distributed from rostral to caudal along the CNS-body axis. Global features of the intra-PNS neuronal network based on node (ganglion) centrality measures identified two hubs (the bilateral myenteric plexus ganglia that control digestive tract functionality), no rich club, and small-world properties comparable to those reported for the rat brain. These findings suggest that the PNS is not merely a series of parallel nerves and associated ganglia but instead forms a structured and recurrently connected neuronal network. Its full extent and functional relevance remain to be elucidated using contemporary structure-function neuroscience approaches.