Severed nerve stumps around a laser-irradiated locus in the deep muscular plexus of the guinea-pig small intestine

Abstract

Small foci of photocoagulation necrosis (diameter about 0.5 mm) were produced in the wall of the guinea-pig small intestine by argon laser irradiation applied to the serosal surface. Features of the nerve elements around the necrotic masses were examined by immunocytochemistry, scanning electron microscopy, and transmission electron microscopy. The severed ends of nerve strands were examined at various intervals from 10 to 60 h after the laser irradiation, and the acute cytological responses of the nerve terminals, glial cells and connective tissue cells were studied. The laser irradiated foci in the deep muscular plexus (plexus muscularis profundus: CAJAL, 1911) had concentric configuration: 1) central necrotic area, 2) inner transitional zone, 3) outer transitional zone, and 4) normal area. In the necrotic area, there were inflammatory cells such as neutrophile leukocytes and macrophages. Contours of the smooth muscle cells and nerve strands were well preserved in spite of the damage to their subcellular structures. In the inner transitional area, individual nerve fibers gathered to form bundles. Some of these nerve bundles were devoid of a glial cell framework. In the outer transitional zone, there were swollen nerve terminals with a strong immunoreactivity for methionine-enkephalin-Arg6-Gly7-Leu6. In transmission electron microscopy, some of these swollen nerve fibers contained many large cored vesicles. Glial cells in the outer transitional zone exhibited an S-100b protein-like immunoreactivity. Scanning electron microscopy revealed gatherings of fibroblast-like (FBL) cells in the outer transitional zone. Two subtypes of these were distinguished: the first subtype (FBL I) was characterized by short, blunt cytoplasmic processes; the second subtype (FBL II), possessing long, slender dendritic processes, assembled to form a dense network which intermeshed with that of the nerve strands. The enteric nerve plexuses severed by laser-irradiation affords a unique experimental model in the cytological investigation of the plasticity of the peripheral autonomic nervous system.