STRUCTURAL DIFFERENCES OF THE ENTERIC NERVOUS-SYSTEM IN THE CATTLE FORESTOMACH REVEALED BY WHOLE-MOUNT IMMUNOHISTOCHEMISTRY

The specific motility pattterns of the forestomach of ruminants, compo sed of three structurally distinct compartments (rumen, reticulum, oma sum), require an elaborate intramural innervation. To demonstrate the complex structure of the enteric nervous system (ENS), whole mount pre parations obtained from different sites of the bovine forestomach were submitted to immunohistochemical procedures in which neuronal (protei n gene product 9.5, neurofilament 200) and glial (protein S-100, glial fibrillary acid protein) markers were applied. Immunohistochemistry p erformed 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 in terconnecting nerve fiber strands, whereas the mucosal plexus consiste d of an aganglionated nerve network. However, the texture of the ENS s howed considerable regional differences concerning the ganglionic size , shape and density and the arrangement of nerve fiber strands. The my enteric plexus of the ruminal wall, showing a low ganglionic density a nd 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 o bserved at the reticular groove, the most prominent ganglia were found within the omasal wall. Branches of the vagal nerve frequently ramifi ed within the myenteric plexus layers. The submucosal plexus of the ru men was divided into an external and internal layer; the reticular sub mucosal plexus followed the cristae and cellulae reticuli, the omasal submucosal (sublaminar) plexus showed intra- and parafascicular gangli a apart from ganglia located at the junctions of the nerve network. Th e mucosal plexus of the rumen consisted of thin nerve fascicles ramify ing between the ruminal papillae, and reticular mucosal nerve fibers p assed throughout the base of the cellulae reticuli. The highly special ised nerve network of the intralaminar omasal plexus showed radial and transverse trajectories reflecting the spatial arrangement of the int ralaminar musculature. The demonstrated structural complexity of the E NS reflects the functional complexity of the ruminant forestomach and indicates the relatively high degree of autonomy in coordinating the d ifferent motility patterns required for the processing of the ingesta.