Electron microscopy of the mucosal plexus of the rat colon

The ultrastructure of neurons, glial cells and axons of the mucosal plexus of the rat colon descendens was studied. Serial semithin sections and a re-embedding technique were used in order to localize the ganglia. The ganglia are free of blood vessels and connective tissue. The ratio of neurons to glial cells is approximately 1. Ganglia and nerve strands are enclosed by a basement membrane, without a well-defined perineural connective tissue. The neurons show a structure similar to other enteric plexus. Synaptic contacts were observed frequently in the neuropil, where nerve endings and varicosities show a diverse outfit in vesicles. The glial cells, which contain immunocytochemically detectable glial fibrillary protein, possess the same ultrastructural attributes in the intra- and extraganglionic localizations. In the nerves, axonic profiles and varicosities appear in close relation with glial cells or their processes. The distance between the nerves and their target cells, i.e. the enterocytes, is 0.5 microns or more with interposed basement membranes and fibroblasts.