Regenerating peripheral axons transport and release low-molecular-mass materials in vitro

The release of radiolabeled material from regenerating frog sciatic nerves was studied using a multicompartment chamber, in which the ganglia and the outgrowth region, respectively, were separated from the rest of the nerve. The nerves were incubated with radioactive amino acids in the ganglionic compartment, and the material transported to and released at the outgrowth region was collected and analyzed. Approximately 10% of the transported radioactivity was released over a 24-h incubation period. Of the released materials, 84% had a molecular mass of < 1,000 daltons [the low-molecular-mass (LM) fraction] as determined by exclusion chromatography. The presence of LM material could not be explained by leakage, nor was it due to intracellular or extracellular degradation of radiolabeled, transported proteins. It was reduced by cold and was shown by the use of vinblastine to be dependent on axonal transport. According to TLC, both the original precursor and metabolites thereof could be detected among the released LM material. The present results demonstrate the existence of a transport system for LM material in peripheral axons. The preferential release of LM over high-molecular-mass material at the outgrowth region suggests that it could serve specific functions during regeneration.