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Damage to the sciatic nerve produces significant changes in the relative synthesis rates of some proteins in dorsal root ganglia and in the amounts of some fast axonally transported proteins in both the sciatic nerve and dorsal roots. We have now analyzed protein synthesis and axonal transport after cutting the other branch of dorsal root ganglia neurons, the dorsal roots. Two to three weeks after cutting the dorsal roots, [35S]methionine was used to label proteins in the dorsal root ganglia in vitro. Proteins synthesized in the dorsal root ganglia and transported along the sciatic nerve were analyzed on two-dimensional gels. All of the proteins previously observed to change after sciatic nerve damage were included in this study. No significant changes in proteins synthesized in dorsal root ganglia or rapidly transported along the sciatic nerve were detected. Axon regrowth from cut dorsal roots was observed by light and electron microscopy. Either the response to dorsal root damage is too small to be detected by our methods or changes in protein synthesis and fast axonal transport are not necessary for axon regrowth. When such changes do occur they may still aid in regrowth or be necessary for later stages in regeneration.

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The mechanisms underlying directed axonal movement in the developing central nervous system are largely unknown. Histochemical methods for transmission and scanning electron microscopy were used to study the surface of the developing optic tectum in the chick embryo at the time of optic fiber ingrowth. A highly structured extracellular matrix consisting of fibrillar and granular components was seen in normal and in uninnervated specimens that had been fixed in solutions containing the cationic dyes Alcian blue, ruthenium red, or safranin O. The strong affinity of these stains for glycosaminoglycans suggests that the matrix contains such macromolecular aggregates. With routine fixation methods the matrix was not seen, but empty extracellular spaces were apparent. The tectal matrix was particularly prominent ahead of the growing front of optic fibers. Its location was thus appropriate for interacting with pioneering axons that cross the surface of the developing tectum along its anterior-posterior axis. Matrix fibrils were organized in a stacked alignment predominantly parallel to the tectal surface, but otherwise their orientation appeared random. The matrix possibly bears on the guidance of optic fibers. However, its geometry suggests that this may involve a mechanism more specific than mechanical contact guidance.