Mucosal projections of enteric neurons in the porcine small intestine

In the present study, a combination of immunohistochemistry and retrograde 1,1'-didodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) trac ing was used to unravel the morphology, distribution, and neurochemical cod ing of submucous and myenteric neurons with axonal projections to the mucos a of the porcine small intestine. The majority of traced neurons was locate d in the inner submucous plexus (ISP; 78%), whereas the remaining part was distributed between the outer submucous plexus (OSP; 10%) and myenteric ple xus (MP; 12%). Among these traced neurons, some distinct neuronal populatio ns could be distinguished according to their morphologic and neurochemical properties. In the ISP, several types of traced neurons were detected: 1) m orphologic type II neurons expressing choline acetyltransferase (ChAT) immu noreactivity, calcitonin gene-related peptide (CGRP) immunoreactivity, and substance P (SP) immunoreactivity; 2) ChAT/SP-immunoreactive (-IR) small ne urons; 3) vasoactive intestinal polypeptide (VIP) -IR small neurons; and 4) multidendritic ChAT/somatostatin (SOM) -IR neurons. The traced neuronal po pulations of the OSP and MP were similar to each other. In both plexuses, t he following DiI-labelled neurons were found: 1) ChAT/CGRP/(SP)-IR type II neurons; 2) multidendritic ChAT/SP-IR neurons; and 3) multidendritic ChAT/S OM-IR neurons. Comparison of the present findings with previously obtained data concerning the mucosal innervation pattern of the intestine of small m ammals, revealed significant species differences with respect to the morpho logic and neurochemical features of the involved enteric neuronal classes. Although not identical, a closer resemblance between pig and human enteric nervous system seems to be at hand, as far as the anatomic organization and the presence of neurochemically identified neuronal subtypes within the en teric nervous system are concerned. (C) 2000 Wiley-Liss. Inc.