Chemotropism in nerve regeneration studied in tissue culture.

The neurotropic effect of the distal stump of transected sciatic nerve on regenerating axons emerging from the proximal stump was investigated in rats by the coculture of excised neonatal dorsal root ganglia and segments of degenerated and nondegenerated sciatic nerves. In all cultures, neurites from the ganglion extended directly towards the degenerated distal stump and not towards the undegenerated nerve segment. Analysis of the supernatants of nerve homogenates by native polyacrylamide gel electrophoresis demonstrated that 250 and 18 kDa proteins were upregulated in the degenerated distal stumps and that 89, 67 and 65 kDa proteins were expressed by these stumps but not by normal nerve. Placement of the individual protein strips, cut from the gels, in dissociated cultures of dorsal root ganglion cells showed that the 89 and 18 kDa strips possessed strong neurotropic activity. Neurons survived selectively on these strips and outgrowing neurites elongated on the strips, parallel to the direction of the band. When explanted dorsal root ganglia were cultured along with the strips, outgrowing neurites extended selectively towards those containing the 89 and 18 kDa bands. It is concluded that these bands contain chemotropic substances, the nature of which requires further investigation.