Retrograde transport of horseradish peroxidase in transected axons. 3. Entry into injured axons and subsequent localization in perikaryon.

Horseradish peroxidase (HRP) applied to crushed mouse sciatic nerves diffused through the damaged perineurium into the endoneurium. In the injured area, HRP passed into damaged myelinated and unmyelinated axons forming columns of reaction product, which extended for several millimeters proximally to the lesion. Ultrastructurally, HRP adhered to the inner surface of the axoplasm and to the surfaces of neurotubules and neurofilaments in such columns. At more proximal levels axons contained HRP in vesicular and tubular organelles and, later, nerve cell bodies of the corresponding spinal ganglia showed HRP, accumulation in cytoplasmic vesicles, cup-shaped bodies, multivesicular bodies and tubules of agranular endoplasmic reticulum. Markedly less HRP reached neurons in the spinal ganglia when applied to the nerve 30 or 60 min after the crush. After such time intervals solid HRP containing axons were also less frequently observed. Conceivably, HRP enters crushed axons momentarily after a crush as an injured cell reaction. Subsequently it is incorporated into organelles higher up in the axons, from where retrograde transport to the perikaryon will fellow. This phenomenon of a sudden non-specific influx of exogenous macromolecules into axotomized neurons and their subsequent transport to the perikaryon might be relevant for development of certain biochemical and morphological responses, e.g. lysosomal alterations, of the neuron to an axonal injury.