The influence of ileitis on the neurochemistry of the caudal mesenteric ganglion in the pig

Background Some literature data suggest that there is a regulatory neuronal circuit between the small and the large bowel. To verify this hypothesis the present study investigated: (i) the distribution, chemical coding and routing of caudal mesenteric ganglion (CaMG) neurons participating in an intestinointestinal reflex pathway involving ileal descending neurons and viscerofugal colonic neurons and (ii) possible changes in the neuroarchitecture of this pathway evoked by chemically induced ileitis in juvenile pigs (n = 16). Methods Combined retrograde tract tracing and transections of the intermesenteric or caudal colonic nerves were applied. In addition, double immunostainings was used to investigate the chemical coding of retrogradely labeled CaMG neurons and intraganglionic nerve terminals apposed to them, under normal and inflammatory conditions. Key Results The majority of the ileum‐projecting neurons were found in the caudal part of CaMG. Disruption of particular nerve pathways resulted in diminished number of retrogradely labeled neurons, ipsilateral to the side of manipulation. In normal pigs, ileum‐projecting CaMG neurons stained for tyrosine hydroxylase, dopamine‐β‐hydroxylase, neuropeptide Y (NPY), somatostatin and galanin (GAL). The number and chemical coding of the neurons in the inflamed animals were similar to those observed in the normal pigs. However, in the inflamed pigs, the number of NPY‐, GAL‐ or substance P‐positive nerve terminals supplying retrogradely labeled neurons was increased. Conclusions & Inferences The present results suggest that inflammatory processes of the porcine ileum are able to induce changes in the intraganglionic architecture of a sympathetic ganglion located at discrete distance from the affected bowel segment.