Lysosomal activity at nodes of Ranvier in dorsal column and dorsal root axons of the cat after injection of horseradish peroxidase in the dorsal column nuclei.

The occurrence of acid phosphatase (AcPase)-positive bodies, i.e. lysosomes, in dorsal column and dorsal root axons of the spinal cord segments C8 and L7 in adult cats was analyzed by light and electron cytochemical methods after injection of horseradish peroxidase (HRP) in the dorsal column nuclei. Axonal lysosomes were, with few exceptions, concentrated at the nodes of Ranvier. We found no changes in nodal occurrence and distribution of lysosomes in axons of the HRP-injected sides, as compared to axons of the uninjected sides or of animals not exposed to HRP. Axonal lysosomes were very rare in the dorsal columns, where the frequency of nodes containing light microscopically detectable AcPase-positive bodies was 0-5% at the HRP-injected sides, 0-6% at the contralateral sides, and 0-3% in control animals. The corresponding values in the cervical and lumbar dorsal roots were 6-23%, 9-20%, 10-12% and 19-37%, 21-40%, 26-43%, respectively. In view of our recent observations in alpha-motor neurons, the results point at a noteworthy difference in local degradative ability between dorsal column axons and alpha-motor axons, the latter being able to accumulate intramuscularly injected and retrogradely transported HRP at their PNS nodes of Ranvier for 48-60 h, during which period the axoplasmic AcPase activity/concentration increases at some nodes. Such a degradative activity, which could protect the motor neurons by restricting axoplasmic transport of exogenous materials imbibed by their axon terminals outside the CNS, may not be of the same significance for neurons, e.g. dorsal root ganglion neurons, the axon terminals of which are located within the CNS.