Cytoplasmic, but not nuclear, expression of the neuronal nuclei (NeuN) antibody is an exclusive feature of Dogiel type II neurons in the guinea-pig gastrointestinal tract.

This study aimed to reveal if NeuN, a neuronal nuclei (NeuN) antibody, is a selective marker of intrinsic primary afferent neurons (IPANs) in the guinea-pig gastrointestinal tract as previously hypothesised. The NeuN immunoreactivity was found in the enteric nervous system with exception of the esophagus. Two groups of NeuN-expressing neurons were observed: neurons with immunostained nuclei and cytoplasm (NeuN(NC)) and neurons only expressing immunoreactivity in their nuclei (NeuN(N)). The NeuN(N)-immunoreactive neurons were found in the myenteric plexus of the stomach and the colon. In the stomach, none of the NeuN(N)-expressing neurons, of which 55+/-3% co-expressed calbindin, had a Dogiel type I or II morphology. The NeuN(N)-positive neurons of the colon, which did not express calbindin, did not resemble a Dogiel type II morphology either, but were small-sized neurons. The NeuN(NC)-immunoreactive neurons were observed in both the small and large intestine. These neurons were smooth-contoured and bigger-sized, resembling a Dogiel type II morphology. Some of these neurons co-expressed calbindin. The present data reveal the existence of two populations of Dogiel type II neurons, exhibiting NeuN(NC)+/calbindin+ or NeuN(NC)+/calbindin- immunoreactivity, in the intestine. Assuming that all IPANs exhibit a Dogiel type II morphology, we conclude that the cytoplasmic expression of NeuN is an exclusive feature of IPANs.

Effect of intestinal inflammation on capsaicin-sensitive afferents in the ileum of Schistosoma mansoni-infected mice.

In the present study, the effect of intestinal schistosomiasis on the extrinsic sensory innervation of the murine ileum was investigated. Immunocytochemical techniques to localize calcitonin gene-related peptide (CGRP), substance P (SP), and vanilloid receptor 1 (VR1) were combined with retrograde tracing techniques and capsaicin treatment. Neurochemical characterization of extrinsic primary afferent neurons (EPANs) in normal and capsaicin-treated mice, revealed that CGRP and VR1, but not SP, were expressed in extrinsic afferents. Immunocytochemical analysis using the above-mentioned antibodies yielded three different populations of neurons in both dorsal root and nodose ganglia, namely CGRP/--, SP/--, and CGRP/SP-expressing neurons. Retrograde tracing revealed that only CGRP/--expressing neurons projected to the ileum. Intestinal schistosomiasis resulted in an upregulation of the number of CGRP-immunoreactive (ir) nerve fibers in the lamina propria of the villi, coinciding with an increase in mucosal mast cells in acutely and chronically infected animals. In infected animals, mucosal mast cells were found closely associated with a dense mucosal CGRP-ir fiber network. Neonatal capsaicin treatment led to a 70% reduction in the number of mucosal mast cells. In conclusion, the present study provides evidence that CGRP is a valid marker for EPANs in the mouse ileum, which are involved in the recruitment of mucosal mast cells. Morphological evidence is provided of a neuroimmune interaction between mucosal mast cells and EPANs in schistosoma-infected mice.

Temporal distribution of distinct mast cell phenotypes during intestinal schistosomiasis in mice.

Mastocytosis is a common feature of helminth infection in most host species. We examined the temporal distribution and phenotype of mast cells during intestinal schistosomiasis in mice, using antibodies directed against histamine, a general mast cell marker, against mouse mast cell protease-1 (MMCP-1), a mucosal mast cell (MMC) marker, and against tryptase, a predominantly connective tissue mast cell (CTMC) marker. Ileal paraffin and/or cryosections of control, 8- and 15-week-infected mice were quantitatively analysed. In the intestinal wall of non- and unisexual infected mice, a few dispersed mast cells were detected. In infected mice, a transient increase of mast cells in the mucosa and a gradual increase in the outer muscle layer were observed. MMCP-1 expressing MMCs were predominantly present in the mucosa during the acute phase [8 weeks postinfection (p.i.)], while tryptase and histamine immunoreactivity demonstrated that two subsets of CTMCs were predominantly present in the outer muscle layer at 15 weeks p.i. (chronic phase). In conclusion, these results reveal that, in mice, both MMCs and CTMCs are involved in the inflammatory response during schistosomiasis. The recruitment of each mast cell population is time-dependent and occurs at different locations. These data suggest that mastocytosis is associated with motility-related gastrointestinal symptoms and egg excretion.