Primary degeneration of motor neurons by toxic lectins conveyed from the peripheral nerve.

In attempts to degenerate motor neurons experimentally by way of retrograde axoplasmic transport, ricinus communis agglutinin (RCA), a potent protein inhibitor, was intraneurally injected into the rat sciatic nerve. Immunohistochemically, RCA was shown to be intra-axonally carried up to motor neuronal soma and to the dorsal root ganglia of L4-6. Within a few days, these dorsal root ganglion cells and large motor neurons giving rise to sciatic nerve efferents in the lumbar spinal cord degenerated, whereas small internuncial neurons and glia remained unaffected. The degeneration of motor neurons was characterized by a profound diffuse chromatolysis and subsequent dissolution, after which a mild gliosis remained. The retrograde axoplasmic flow of neurotoxic substance and motor neuron degeneration observed here may be a phenomenon implicated in the pathogenesis of human motor neuron diseases.