Electron microscopial localization of 5'-nucleotidase in the rat peripheral nerve fibers by cerium-based cytochemistry.

To extend our earlier studies on the subcellular distribution of 5'-nucleotidase in peripheral nerve fibers, we have applied the cytochemical method with cerium ions as trapping agents for inorganic phosphate released from adenosine-5'-monophosphate. Adult and 15-day-old Wistar rats were investigated. In myelinated nerve fibers, 5'-nucleotidase activity was visualized mainly on the Schwann cell plasma membrane, the axolemma, the surface of the myelin sheath and its widened lamellae in the paranodal areas, and Schmidt-Lanterman clefts. Single reaction precipitates were observed at the intraperiod lines of the compact myelin. In addition, in the young animals, the nuclear envelope and the rough endoplasmic reticulum were also found associated with reaction deposits. The simple axon-Schwann cell sheaths of the unmyelinated nerve fibers were also reactive. The cerium-based method reveals a pattern of localization of the 5'-nucleotidase in peripheral nerve fibers quite similar to that detected by the conventional lead-based method. The cerium-based method, however, determines a more uniform distribution of finer reaction deposits along the cellular membranes. In young rats, the enzyme reaction was found to be more intense, especially in the areas of myelin-forming membranes.