Completeness and selectivity of ricin "suicide transport" lesions in rat dorsal root ganglia

Ricinus communis agglutinin (MW 60kDa type, RCA₆₀, ricin) injected into the rat sciatic nerve produces massive degeneration of cells in those dorsal root ganglia (DRGs) known to contain the sensory cells-of-origin of the sciatic nerve. We have evaluated the extent of this cell death quantitatively. Using 1 or 2 μg RCA₆₀, the average proportion of L₅ DRG neurons destroyed closely matched the proportion of neurons in this ganglion known to have an axon in the sciatic nerve. A lower dose, 0.2 μg ricin, produced substantially less cell death. There was heavy fiber degeneration in the sciatic nerve proximal to the injection site, but not in a nearby tributary nerve with which it shares the L₅ DRG. Furthermore, the topographic distribution of Fink-Heimer argyrophilia corresponded to the known sciatic nerve distribution. The data suggest that at appropriate doses toxic ricin can produce a near complete and selective lesion by retrograde "suicide transport".