title: 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.
authors.affiliation: Institute of Anatomy I, University of Erlangen-Nuremberg, Erlangen, Germany.
authors.forename: Sonja
authors.initials: S
authors.lastname: Kapp
authors.forename: Falk
authors.initials: F
authors.lastname: Schrödl
authors.forename: Winfried
authors.initials: W
authors.lastname: Neuhuber
authors.forename: Axel
authors.initials: A
authors.lastname: Brehmer
mesh_terms: D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000032:analysis; D002795:Choline O-Acetyltransferase / Q000032:analysis; D051959:ELAV Proteins / Q000032:analysis; D004745:Enkephalins / Q000032:analysis; D005260:Female; D005725:Ganglia, Autonomic / Q000737:chemistry / Q000166:cytology; D007082:Ileum / Q000737:chemistry / Q000166:cytology* / Q000293:injuries; D007150:Immunohistochemistry / Q000379:methods; D007211:Indoles / Q000737:chemistry; D008297:Male; D016900:Neurofilament Proteins / Q000032:analysis; D009474:Neurons / Q000737:chemistry / Q000166:cytology*; D052248:Nitric Oxide Synthase Type I / Q000032:analysis; D009942:Organometallic Compounds / Q000737:chemistry; D013004:Somatostatin / Q000032:analysis; D013368:Submucous Plexus / Q000737:chemistry / Q000166:cytology*; D013552:Swine
chemical_list: D051959:ELAV Proteins; D004745:Enkephalins; D007211:Indoles; D016900:Neurofilament Proteins; D009942:Organometallic Compounds; C015445:copper phthalocyanine; D013004:Somatostatin; D052248:Nitric Oxide Synthase Type I; D002795:Choline O-Acetyltransferase; D015740:Calcitonin Gene-Related Peptide