Inflammation-Induced Changes in the Chemical Coding Pattern of Colon-Projecting Neurons in the Inferior Mesenteric Ganglia of the Pig

The present study examines the chemical coding of the inferior mesenteric ganglia after chemically induced colitis in the pig animal model. In all animals (n=6), a median laparotomy was performed under anesthesia, and the Fast Blue retrograde tracer was injected into the descending colon wall. In experimental animals (n=3), the thick descending colon were injected with formalin solution to induce inflammation. The animals were euthanized and the inferior mesenteric ganglion was harvested and cessed for double-labeling immunofluorescence for calbindin-D28k (CB) in combination with either tyrosine hydroxylase (TH), neuropeptide Y (NPY), somatostatin (SOM), vasoactive intestinal polypeptide (VIP), nitric oxide synthase (NOS), Leu-enkephalin (LENK), substance P (SP), vesicular acetylcholine transporter (VAChT), or galanin (GAL). Immunohistochemistry revealed significant changes in the chemical coding pattern of inferior mesenteric ganglion neurons. In control animals, Fast Blue-positive neurons were immunoreactive to TH, NPY, SOM, VIP, LENK, CB, and NOS. In the experimental group, TH, NPY, SOM, VIP, and LENK expressing neurons were reduced, whereas the number of neurons immunoreactive to CB, NOS, and GAL were increased. The increase of so-called neuroprotective neuropeptides suggests that the changes in the chemical coding of inferior mesenteric ganglion neurons reflect adaption under pathological conditions to promote their own survival.