Membrane biogenesis in the sprouting neuron. I. Selective transfer of newly synthesized phospholipid into the growing neurite

Our goal was to elucidate the pathway of newly synthesized phospholipid into the growing neurite. This was accomplished in pulse-chase studies with the phospholipid precursor [3H]glycerol, using sprouting explant cultures of rat superior cervical ganglion as an experimental system. After the pulse with the precursor and various chase periods, we separated perikarya and neurites microsurgically and extracted their phospholipids. The phospholipid extract from the perikarya exhibited a steep rise followed by a rapid decline in specific radioactivity. In contrast, an increase in neuritic specific radioactivity of phospholipid was observed only after a lag period of approximately 60 min. Nearly quantitative transfer of newly synthesized phospholipid from the perikarya into the neurites could be demonstrated. Both the decline in perikaryal specific radioactivity and the increase in its neuritic counterpart, i.e., the proximodistal transfer, could be blocked with the microtubule drug colchicine and the metabolic uncoupler, 2,4-dinitrophenol. These observations indicate preferential export of newly synthesized phospholipid from the perikaryon (the major or exclusive site of synthesis) into the growing neurites, most likely by rapid axoplasmic transport of formed elements.