Identification of intrinsic primary afferent neurons in mouse jejunum

Background: The gut is the only organ system with intrinsic neural reflexes. Intrinsic primary afferent neurons (IPANs) of the enteric nervous system initiate intrinsic reflexes, form gut-brain connections, and undergo considerable neuroplasticity to cause digestive diseases. They remain inaccessible to study in mice in the absence of a selective marker. Advillin is used as a marker for primary afferent neurons in dorsal root ganglia. The aim of this study was to test the hypothesis that advillin is expressed in IPANs of the mouse jejunum. Methods: Advillin expression was assessed with immunohistochemistry and using transgenic mice expressing an inducible Cre recombinase under the advillin promoter were used to drive tdTomato and the genetically encoded calcium indicator GCaMP5. These mice were used to characterize the morphology and physiology of advillin-expressing enteric neurons using confocal microscopy, calcium imaging, and whole-cell patch-clamp electrophysiology. Key Results: Advillin is expressed in about 25% of myenteric neurons of the mouse jejunum, and these neurons demonstrate the requisite properties of IPANs. Functionally, they demonstrate calcium responses following mechanical stimuli of the mucosa and during antidromic action potentials. They have Dogiel type II morphology with neural processes that mostly remain within the myenteric plexus, but also project to the mucosa and express NeuN and calcitonin gene-related peptide (CGRP), but not nNOS. Conclusions and Inferences: Advillin marks jejunal IPANs providing accessibility to this important neuronal population to study and model digestive disease.