Neuroglial response to neuron injury. A study using intraneural injection of ricinus communis agglutinin-60.

The present study has shown the selective destruction of large ventral horn neurons in the lumbosacral cord segments following a single injection of RCA-60 into the sciatic nerve. The neurons appeared to undergo structural alteration beginning 3 days after the RCA application. In the postoperative period extending from 1 to 60 days, degeneration of neurons was progressive and irreversible and this elicited a rapid increase in the number of microglial cells. They were most numerous in the 7 days postoperative animals. The massive microglial cells penetrated the neuropil and appeared to strip off the axon terminals from the postsynaptic somata. Occasional axon terminals were phagocytosed by microglia. The numerous microglial cells often formed a multilayered 'barrier' encircling the somata of the RCA-poisoned neurons which eventually became totally disorganised. It is postulated that in the course of neuronal degeneration induced by RCA, microglial cells serve to prevent the leakage or diffusion of the toxic lectin from the neuronal somata into the neighbouring neuropil. They also function as scavenger cells in the removal of degenerating myelinated axons in the longer surviving rats. Oligodendrocytes do not appear to react actively to the degeneration process. However, astrocytes showed a significant increase in the 7 and 15 day postoperative rats and this coincided with the presence of mitotic astrocytes in the same period.