CHANGES IN FAST AXONAL-TRANSPORT IN SENSORY NEURONS DURING TADPOLE METAMORPHOSIS

Fast axonal transport of radiolabeled protein was examined in lumbar a nd tail dorsal root ganglion (DRG) neurons at progressive stages of bu llfrog tadpole metamorphosis. Accumulation of [S-35]methionine-labeled protein proximal to a lumbar peripheral nerve ligature (at a fixed di stance from the DRG) increased as tadpoles advanced from premetamorpho sis through prometamorphosis to metamorphic climax. The rate of increa se was steeper when expressed as a percentage of protein synthesized i n the neurons of origin than when expressed as a percentage of total D RG protein synthesis. Further, the increase was not secondary to a ris e in protein synthesis. In contrast, fast axonal transport decreased i n DRG neurons of the tail at the onset of metamorphic climax, when tai l resorption is initiated. The stage-related increase in protein trans port in lumbar nerves is due, at least in part, to an increased rate o f transport. As determined from optically detected anterograde organel les in individual lumbar nerve axons, an approximate doubling of the f ast transport rate occurred between the premetamorphic stage and metam orphic climax. In addition, the rates of organelle transport in lumbar axons of adult bullfrogs were significantly greater than in correspon ding axons of tadpoles at metamorphic climax, further suggesting that organelle velocity is a developmentally regulated parameter of fast ax onal transport.