Structural organization of the enteric nervous system in the cattle esophagus revealed by wholemount immunohistochemistry.

In ruminants the motility patterns of the esophageal tube are characterized by physiological regurgitations including both anterograde and retrograde peristaltic movements. These complex motor functions require an elaborated enteric nervous system (ENS) for the generation of the underlying intrinsic reflex circuits. The structural organization of the esophageal ENS was studied in fetuses of cattle (n=6) by means of wholemount preparations obtained from different segments of the esophagus. Demonstration of nerve cells, ganglia and nerve fibers strands (NFS) was achieved by immunohistochemistry using the general neuronal marker protein gene product (PGP) 9.5. The myenteric plexus represented the most prominent nerve network composed of differently shaped ganglia and interconnecting NFS. Frequenitly the myenteric ganglia were arranged in two separate layers interweaving with the adjacent muscle coat. From the cervical towards the thoracic segment of the esophagus the density and size of myenteric ganglia increased and the NFS exhibited thicker diameters. The submucosal and mucosal plexus consisted of NFS ramifying throughout the tela submucosa and the lamina propria mucosae. The networks showed no evidence of ganglia nor single nerve cells. The findings illustrate that intrinsic esophageal nerve cells are confined to the myenteric plexus. Since the esophageal tube has no secretory functions, secreto-motor neurons are not required in the submucosal and mucosal plexus layers. The structural organization of the intramural nerve networks--in particular the specific arrangement of the myenteric plexus--reflects the substantial contribution of the esophageal ENS to the coordination and mediation of esophageal motility in ruminants.

Structural differences of the enteric nervous system in the cattle forestomach revealed by whole mount immunohistochemistry.

The specific motility patterns of the forestomach of ruminants, composed of three structurally distinct compartments (rumen, reticulum, omasum), require an elaborate intramural innervation. To demonstrate the complex structure of the enteric nervous system (ENS), whole mount preparations obtained from different sites of the bovine forestomach were submitted to immunohistochemical procedures in which neuronal (protein gene product 9.5, neurofilament 200) and glial (protein S-100, glial fibrillary acid protein) markers were applied. Immunohistochemistry performed on whole mounts allowed a detailed two-dimensional assessment of the architecture of the intramural nerve networks. Generally, the myenteric and submucosal plexus layers were composed of ganglia and interconnecting nerve fiber strands, whereas the mucosal plexus consisted of an aganglionated nerve network. However, the texture of the ENS showed considerable regional differences concerning the ganglionic size, shape and density and the arrangement of nerve fiber strands. The myenteric plexus of the ruminal wall, showing a low ganglionic density and wide polygonal meshes, contrasted with the nerve network within the ruminal pillar which consisted of ropeladder-like nerve fiber strands and parallel orientated ganglia. The highest ganglionic density was observed at the reticular groove, the most prominent ganglia were found within the omasal wall. Branches of the vagal nerve frequently ramified within the myenteric plexus layers. The submucosal plexus of the rumen was divided into an external and internal layer; the reticular submucosal plexus followed the cristae and cellulae reticuli, the omasal submucosal (sublaminar) plexus showed intra- and parafascicular ganglia apart from ganglia located at the junctions of the nerve network. The mucosal plexus of the rumen consisted of thin nerve fascicles ramifying between the ruminal papillae, and reticular mucosal nerve fibers passed throughout the base of the cellulae reticuli. The highly specialised nerve network of the intralaminar omasal plexus showed radial and transverse trajectories reflecting the spatial arrangement of the intralaminar musculature. The demonstrated structural complexity of the ENS reflects the functional complexity of the ruminant forestomach and indicates the relatively high degree of autonomy in coordinating the different motility patterns required for the processing of the ingesta.