Acid phosphatase activity at nodes of Ranvier in alpha-motor and dorsal root ganglion neurons of the cat.

Acid phosphatase (AcPase) activity in feline alpha-motor and dorsal root ganglion (DRG) neurons was analysed histochemically by light and electron microscopy. The occurrence and distribution of the AcPase activity expressed within the axon differed depending on neuron type and distance from the cell body. Both in alpha-motor and DRG neurons, AcPase-positive bodies of various morphological categories were observed mainly at nodes of Ranvier, where they were more frequent distal than proximal to the nodal midlevel. In the peripherally located processes of both neuron types, most of the larger AcPase-positive bodies were associated with the paranodal axon-Schwann cell network. In the centrally located processes the AcPase-positive bodies were situated in the constricted axon segment and the adjacent paranodal axoplasm. Both in motor and DRG axons, AcPase-positive bodies were more frequent at the spinal root level than at a level central to the PNS-CNS borderline. The observations indicate that lysosomes (i.e. AcPase-positive bodies) constitute part of the intra-axonal system of organelles in normal, large, myelinated alpha-motor and DRG axons of the cat. Lysosome-mediated degradation of retrogradely transported endogenous and exogenous materials may be extensive in normal peripherally directed neuronal processes. The study also suggests a difference between PNS and CNS parts of the same axon with regard to the local turnover of lysosomal organelles.