GPER and ER receptors are involved in the regulation of GI motility and visceral pain. Both may thus constitute an important pharmacological target in the IBS-D therapy.

The morphological classification of the different neuronal cell types is generally accepted and expanded by us; nevertheless, immunohistochemically and electrophysiologically the existence of clear-cut categories of enteric neurons is frequently questioned. The immunohistochemical results demonstrated in this study, however, provide the first direct link between a morphological type of enteric neuron and an immunohistochemical staining for a distinct peptide. Evidence demonstrates that calcitonin gene-related peptide occurs in only one morphologically defined type of neuron, viz. in type II neurons, and can therefore be regarded as a ‘marker peptide’ for type II neurons. Hence, the present immunohistochemical findings illustrate the validity of the morphological classification of the enteric neurons.

The presence of nitric oxide-synthase (NOS) in neurons of the porcine inferior mesenteric ganglion (IMG) has been investigated. A minority (about 1-3%) of the neurons were immunoreactive (IR) for NOS, the vast majority of which stained for neuropeptide Y (NPY) but not for tyrosine hydroxylase (TH). A small subpopulation of prevertebral neurons, 1% of which stained for NOS or NADPH-diaphorase (NADPHd), projected to the ductus deferens, as demonstrated by retrograde tracing. Within the wall of the ductus deferens, NOS- or NOS/NPY-IR nerve fibres were found to innervate the smooth muscle or were closely associated with blood vessels. It is therefore suggested that nitric oxide might be involved in the regulation of local blood flow and muscular tone in the wall of the pig ductus deferens.

Studies of the intrinsic and extrinsic innervation patterns of esophageal motor endplates (MEPs) are mainly confined to small rodents. Therefore, an immunocytochemical, denervation and tracing study was conducted on the pig, an experimental model in which the distribution of the striated esophageal muscle portion more closely resembles the human situation. The purpose of this study was to analyze the origin and neurochemical content of the nerve fibers participating in the myoneural synapse. Fifteen 6-week-old domestic pigs were studied by immunohistochemistry combined with a-bungarotoxin labeling to define the co-innervation patterns of nitrergic and peptidergic nerve terminals in MEPs. Some animals were subjected to unilateral infra-or supranodose vagotomy to determine the origin of the nerve terminals in MEPs. Special attention was paid to the interregional differences in terms of co-innervation rates, and these findings were compared with literature data on small mammals. Double stainings revealed that most of the nNOS-immunoreactive (ir) terminals in MEPs co-stained for VIP, GAL and NPY, but not for PACAP and L-ENK. PACAP-and L-ENK-ir terminals were coarser than nNOS-ir terminals, and largely co-localized VAChT. High percentages of MEPs at the cervical level were contacted by PACAP-(~94%) and L-ENK-ir (~78%) terminals, but the proportion of both decreased in the rostrocaudal direction. Vagotomy significantly reduced their presence in MEPs at the thoracic and abdominal levels, while nNOS-ir terminals observed in approximately 30% of the MEPs were unaffected by vagotomy. Immunostainings on brainstem cryosections after retrograde tracing from the cervical esophagus showed that a large number of FB-positive cells in the nucleus ambiguus were PACAP-ir (~72%). C-kit-positive interstitial cells of Cajal were seen adjacent to the striated muscle fibers, apparently without direct relationship to MEPs. Similar to mouse esophagus, intrinsic nitrergic fibers were found to run close to, or even spiral around, these interstitial cells, an association that might point to a role as specialized spindle proprioceptors. In conclusion, the cholinergic terminals -part of which coexpress PACAP and/or L-ENK -that innervate MEPs in the porcine esophagus have a vagal origin, whereas the nNOS/VIP/GAL/NPY-ir fibers co-innervating these MEPs are intrinsic in nature. The regional differences observed along the esophageal length pertain to the neurochemical content of the vagal motor innervation of the MEPs.

The occurrence and distribution of neuroepithelial endocrine (NEE) cells was demonstrated electron- and fluorescence-microscopically in the lungfish Protopterus aethiopicus. They were only found to occur solitarily in the basal part of the ciliomucous epithelium which is restricted to the pneumatic duct and adjacent parts of the common anterior chamber. The NEE cells show a yellow, formaldehyde-induced fluorescence. Electron-microscopically, all the NEE cells are characterized by membrane-bound electron-dense secretory granules with varying diameters, ranging from 75 to 150 nm. These granules are distributed throughout the cytoplasm with a higher concentration in the basal region. The NEE cells were regularly found to contain paracrystalline inclusions with a tubule-like substructural arrangement. A small part of the NEE cells appeared to reach the luminal surface by means of a long slender process bearing specialized beaded microvilli on its apical pole. Intraepithelial nerve fibres with the ultrastructural characteristics of afferent fibres, were found running parallel to the airway surface. Nerve profiles, largely resembling the latter, can be seen in the proximity of the basolateral plasma membrane of the NEE cells. In addition nerve terminals containing an aggregation of small clear vesicles are in close contact with the NEE cells. In conclusion it appears that as has so far been assumed in higher vertebrates the NEE cells in the lung of Protopterus may perceive changes in the airway gasses whereupon they could respond by releasing a chemical modulator, influencing contacting afferent nerve terminals or nearby smooth muscle bundles. Furthermore, intraepithelial nerve fibres or NEE cells might be stretch-sensitive.