Mucosal projections of enteric neurons in the porcine small intestine

Abstract

In the present study, a combination of immunohistochemistry and retrograde 1,1`‐didodecyl‐3,3,3`,3`‐tetramethylindocarbocyanine perchlorate (DiI) tracing was used to unravel the morphology, distribution, and neurochemical coding of submucous and myenteric neurons with axonal projections to the mucosa of the porcine small intestine. The majority of traced neurons was located in the inner submucous plexus (ISP; 78%), whereas the remaining part was distributed between the outer submucous plexus (OSP; 10%) and myenteric plexus (MP; 12%). Among these traced neurons, some distinct neuronal populations could be distinguished according to their morphologic and neurochemical properties. In the ISP, several types of traced neurons were detected: 1) morphologic type II neurons expressing choline acetyltransferase (ChAT) immunoreactivity, calcitonin gene‐related peptide (CGRP) immunoreactivity, and substance P (SP) immunoreactivity; 2) ChAT/SP‐immunoreactive (‐IR) small neurons; 3) vasoactive intestinal polypeptide (VIP) ‐IR small neurons; and 4) multidendritic ChAT/somatostatin (SOM) ‐IR neurons. The traced neuronal populations of the OSP and MP were similar to each other. In both plexuses, the following DiI‐labelled neurons were found: 1) ChAT/CGRP/(SP)‐IR type II neurons; 2) multidendritic ChAT/SP‐IR neurons; and 3) multidendritic ChAT/SOM‐IR neurons. Comparison of the present findings with previously obtained data concerning the mucosal innervation pattern of the intestine of small mammals, revealed significant species differences with respect to the morphologic 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 enteric nervous system are concerned. J. Comp. Neurol. 421:429–436, 2000. © 2000 Wiley‐Liss, Inc.

Outer submucous plexus: An intrinsic nerve network involved in both secretory and motility processes in the intestine of large mammals and humans

“…In the human small and large intestine (Porter et al, 1999;Timmermans et al, 2000), a proportion of the VIP-IR neurons in the OSP, resembling the VIP/GAL-minineurons in the pig intestine, appears to project to the mucosa as well. Additionally, in contrast to the situation in experimental animals reported so far (Song et al, 1991(Song et al, , 1992Hens et al, 2000a), mucosa-projecting neurons colocalizing SOM and SP were observed in the OSP and MP of the human small intestine . Both in vitro and in vivo experiments have shown that neuronal SOM can negatively affect secretion induced by a.o.…”

“…Retrograde DiI tracing from a mucosal villus revealed the presence of multidendritic uniaxonal neurons in all ganglionic nerve networks in porcine and human small intestine (Brehmer et al, 1999;Hens et al, 2000a;Timmermans et al, 2000). Combined DiI tracing and immunohistochemistry clearly demonstrated that in the porcine small intestine, the OSP harbours at least two neurochemically distinct multidendritic populations of cholinergic neurons with axonal projections to the mucosa, namely, one co-expressing SP ( Fig.…”

“…In the guineapig small intestine, DiI-labeled neurons traced from the mucosa are more or less equally distributed between the submucous plexus and the myenteric plexus (Song et al, 1991) and 97% of the traced myenteric neurons exhibit a type II morphology, and are assumed to be primary afferent in nature. In the pig small intestine, DiI-labeled neurons observed in the OSP and MP constitute a minority of the total number of neurons traced from the mucosa (about 10% each; Hens et al, 2000a), whereas in the human small intestine the OSP harbours 54% of the neurons traced from the mucosa (ISP: 12%; intermediate submucous plexus: 10%; and MP: 24%) . The proportion of neurons traced from the mucosa in the ISP of the human colon (51%) (Porter et al, 1999) is comparable with that found in the human small intestine.…”

“…1; neuron 5; Table 1), which were choline acetyltransferase (ChAT)/calcitonin gene-related peptide (CGRP)-immunoreactive (IR). Some of these neurons also stained for substance P (SP) (Hens et al, 2000a).…”

Tachykinins and their functions in the gastrointestinal tract

“…They also project to the mucosa [85]. Retrograde tracing shows that tachykinin-immunoreactive neurons located in the submucosal plexus in the pig small intestine [86] and guinea pig large intestine [87] also project to the mucosa. Moreover, in humans, neurons labeled from 298 Y. Shimizu et al Tachykinins in the gastrointestinal tract the mucosa were located in all ganglionated nerve networks, including the myenteric plexus, in the small intestine and they were immuoreactive for tachykinins [88].…”