Chemical Coding of Submucosal Type V Neurons in Porcine Ileum

Abstract

In this study, we attempted to determine the proportion of type V neurons relative to the putative whole neuron population in the two submucosal plexuses of pigs identified by their neurofilament immunoreactivity. The total neuron number was estimated in cuprolinic blue (CB)/anti-Hu protein (HU) costained wholemounts as the sum of the number of CB+/HU+, CB+/HU– and CB–/HU+ neurons. In the external submucosal plexus (ESP), HU labelled 98.6% and CB 97.3% of neurons. In the internal submucosal plexus, HU labelled 98.3%, whereas CB only marked 92.5% of neurons. Furthermore, we investigated the chemical coding of submucosal type V neurons and searched for submucosal, non-type V neurons displaying the same chemical coding as the myenteric type V neurons described earlier, i.e. the colocalization of calcitonin gene-related peptide (CGRP) and somatostatin (SOM). In order to facilitate immunohistochemical detection of neuroactive peptides, ileal segments were pretreated with colchicine prior to fixation. Type V neurons in the ESP occurred either as single cells displaying one or few prominent dendrite(s) or within aggregates displaying a dendritic tangle. In this plexus, type V neurons amounted to between 0.9 and 1.6% of all CB-stained neurons. ESP type V neurons displayed immunoreactivities for choline acetyl transferase (95.8%) and leucine-enkephalin (73.9%). All type V neurons were negative for neuronal nitric oxide synthase. Fifty-eight percent of ESP CGRP/SOM co-immunoreactive neurons displayed type V morphology, whereas 42% were non-type V neurons. Thus, the chemical coding of ESP type V neurons is in principal similar to that of the myenteric type V neurons described earlier. In the internal submucosal plexus, we found no type V neurons. In this plexus, 0.2% of all neurons counterstained with HU displayed CGRP/SOM coreactivity. As had been observed earlier concerning the myenteric type V neurons, ESP type V neurons were also closely apposed by conspicuous accumulations of boutons reactive for the same markers as the neurons themselves. Although we cannot exclude that axons of CGRP/SOM-reactive enteric, non-type V or extrinsic neurons end synaptically on type V neurons, we suggest that the main synaptic input to type V neurons originates from other type V neurons. This presents an argument for an interneuronal role of type V neurons.

Architecture and Chemical Coding of the Inner and Outer Submucous Plexus in the Colon of Piglets

“…The OSP displayed a wider meshwork with a lower number of ganglia per cm 2 than the ISP in the porcine colon. This observation is in accordance with findings from the porcine ileum and the human colon, where the ISP also forms a denser network than the OSP [ 7 , 19 – 21 ].…”

Chagasic megacolon: enteric neurons and related structures

“…As to their neuronal compositions, we have hitherto found only quantitative differences between the human internal and external submucosal plexus (see below). This is in contrast, e.g., to the pig, where clear qualitative differences between the two submucosal plexus were described (Stach 1977; Timmermans et al 2001; Kapp et al 2006). …”

Mycotoxins and the Enteric Nervous System

“…The first of them is the myenteric plexus located (similarly to rodents) between the longitudinal and circular muscle layer [ 45 , 46 ]. Moreover, two types of submucous plexuses located in the submucous layer of the intestinal wall have been observed: outer submucous plexus—located in close association with the adjacent circular muscle layer (on its inner side) and the inner submucous plexus—positioned closer to the intestinal lumen, near the muscularis mucosae [ 47 , 48 , 49 ]. These plexuses are also often named after their discoverers.…”