The action of puromycin and cycloheximide on the initiation of rapid axonal transport in amphibian dorsal root neurones.

1. Amphibian dorsal root ganglia-sciatic nerve preparations were incubated in vitro and the rapid axonal transport of radioactive labels was studied with a position-sensitive detector and by conventional liquid scintillation analysis. Protein was labelled by exposure of the ganglia to [(35)S]methionine or [(3)H]leucine and lipid was labelled using [(32)P]orthophosphoric acid.2. Protein synthesis was interrupted by exposure of the ganglia to either cycloheximide or puromycin. When ganglia were exposed to either inhibitor prior to or simultaneously with a label, the somal export of both protein and lipid to the axon was reduced by two to three orders of magnitude.3. Using the position-sensitive detector, [(35)S]methionine was observed to be exported from the ninth dorsal root ganglia of Rana catesbiana 3.49+/-1.56 h (+/- S.D.) after exposure, and [(32)P]phosphate 4.46+/-1.85 h after exposure.4. Export of [(35)S]methionine or [(32)P]phosphate was disrupted 3.32+/-1.21 h (+/- S.D.) or 1.93+/-1.04 h respectively after exposure of the ganglia to cycloheximide or puromycin.5. For a given preparation the time required for [(35)S]methionine to be exported was statistically equal to the time required for cycloheximide or puromycin to disrupt export. No such correlation was found to exist for the export of [(32)P]phosphate.6. Analysis revealed that materials labelled with either [(35)S]methionine or [(32)P]phosphate continue to be exported from the ganglia for several hours after the initial disruption in outflow caused by the inhibitors.7. The results do not provide support for the hypothesis of Ambron, Goldman & Schwartz (1975) that a ;key' newly synthesized, and non-storable, polypeptide is added to an already assembled structure to allow rapid axonal transport to be initiated.