The organisation of the enteric nervous system in the submucous and mucous layers of the small intestine of the pig studied by VIP and neurofilament protein immunohistochemistry

The arrangement of the enteric ganglia and nerve fibre plexuses was examined in the submucous and mucous layers and around Peyer's patches of the porcine small intestine to clarify their organisation. Immunohistochemistry of vasoactive intestinal peptide (VIP) and neurofilament proteins in wholemounts, chopped or paraffin sections was used to locate the neural elements. The ganglia of the internal and external submucous plexuses were situated at 2 different topographic locations, being clearly demarcated by the submucosal vascular arcades and differing in neuronal composition. The internal submucous plexus was the only contributor to the plexus surrounding the follicles of Peyer's patches as a continuous mesh of 3 ganglionated nerve subplexuses. VIP-immunoreactive fibres from this mesh innervated the dome. The mucosal plexus, which was subdivided into 4 subunits — the outer proprial, inner proprial, pericryptal and villous plexuses — contained a few solitary neuronal perikarya. Labelling for neurofilament proteins revealed Dogiel types II, IV and VI neurons. The observations reveal several new features in the enteric nervous system of the pig and clarify its nomenclature.