LIGHT AND ELECTRON-MICROSCOPIC DEMONSTRATION OF THE P75 NERVE GROWTH-FACTOR RECEPTOR IN NORMAL HUMAN CUTANEOUS NERVE-FIBERS - NEW VISTAS

The nerve growth factor and its receptor are important in nerve growth , differentiation, maturation, and maintenance, In order to explore th e exact distribution of p75 low-affinity nerve growth factor receptor (p75 NGFr) expression in cutaneous nerve fibers, p75 NGFr and neuron-s pecific enolase double immunofluorescence and immunoelectron microscop ic studies were conducted on normal human skin samples. After p75 NGFr and neuron-specific enolase immunofluorescence double staining, the d ermal nerves were strongly p75 NGFr-immunoreactive (IR); however, very few p75 NGFr-IR nerve fibers were found in the epidermis. p75 NGFr im munoreactivity was found mainly in the peripheral part of cutaneous ne rve trunks and fibers, whereas neuron-specific enolase immunoreactivit y was mainly seen within the axons, After ultrastructural immunostaini ng, the Schwann cell membrane was strongly p75 NGFr-IR. The Schwann ce ll membrane facing the connective tissue was more strongly p75 NGFr-IR than the part of the membrane close to the axon; the Schwann cell cyt oplasm nearest to the membrane sometimes also showed a high p75 NGFr i mmunoreactivity, whereas the rest of the cytoplasm was generally more weakly p75 NGFr-IR; however, the axon itself seldom showed any such im munoreactivity; actually, only a few parts of the axonal membrane reve aled a weak staining, leaving most of the membrane unstained, The axop lasm was not p75 NGFr-IR. The results - that in human cutaneous nerves it is mainly the Schwann cells that express p75 NGFr immunoreactivity - further stress the active role of the glial ensheathment in the con trol and maintenance of a normal target innervation.