The Enteric Nervous System: An Integrative Hub From Development to Systemic Physiology.

The enteric nervous system (ENS) constitutes the largest and most functionally autonomous subdivision of the peripheral nervous system in vertebrates. It orchestrates stereotyped motor programs, secretomotor reflexes, and neuroimmune responses without central input. This review synthesizes evidence from developmental biology, mucosal immunology, and comparative physiology to advance a framework of enteric allostatic plasticity: the proposition that ENS functional resilience arises not from hard-wired reflex arcs but from a conserved capacity for transcriptional and morphological remodeling instructed by the local immune and microbial environment. We first examine the developmental ontogeny of enteric neurons, emphasizing vagal and sacral neural crest contributions, the GDNF-RET chemotactic axis governing colonization, and the hierarchical transcriptional cascades (PHOX2B, ASCL1, HAND2) that specify cholinergic, nitrergic, and serotonergic lineages. We next dissect the molecular architecture of the mature ENS, systematizing neurochemical coding, re-evaluating enteric glial heterogeneity across selected animal species, and describing structural variations in ganglionated plexuses that reflect evolutionary scaling of the gut wall. Functional circuit analysis addresses intrinsic sensory transduction via IPANs and enterochromaffin cells, the coordination of peristaltic and segmental motor patterns, and the neuroimmune circuits linking enteric neurons to muscularis macrophages and the innate lymphoid cells. Finally, we position the ENS as a central hub within bidirectional gut-brain and gut-immune axes, integrating microbial metabolites, stress hormones, and inflammatory signals to maintain intestinal allostasis. A comparative approach, contrasting murine, porcine, zebrafish, and human systems, is a prerequisite for distinguishing fundamental design principles from lineage-specific elaborations and for translating mechanistic insights to clinical and veterinary neurogastroenterology.