Abstract
Anterograde axonal transport of phospholipids occurs at a rate of several hundred millimeters per day. However, although labeled precursors are incorporated into phospholipids in the neuronal cell bodies within several hours, these newly synthesized phospholipids are committed to transport over a much longer period of time. Thus, maximal accumulation of radioactive lipids in axons and nerve endings does not occur for several days (e.g., 4 to 7 days in rat optic tract and sciatic nerve). We have now investigated the retrograde axonal transport of endogenous phospholipid molecules in sensory neurons of rat sciatic nerve. Labeled phospholipids were delivered to axons and nerve endings of these cells by anterograde axonal transport following injection of [2–3H] glycerol into the L5 dorsal root ganglion. At various times following precursor injection two ligatures, 9 mm apart, were applied to the mid-thigh region of the sciatic nerve. Animals were sacrificed 3 to 48 hr after nerve ligation, nerves were dissected and sectioned into 5-mm segments, and phospholipid radioactivity in each segment was determined. The time-dependent accumulation of labeled phospholipids distal to the distal ligature demonstrated their retrograde axonal transport. The time course of retrograde transport for these phospholipids was more prolonged and peaked several days later than the time course for the anterograde transport phase. Further information regarding the relationship between radioactive phospholipids arriving at the nerve endings by anterograde transport, and their subsequent “turn-around” and retrograde transport back to the nerve cell bodies, was obtained by analyzing the phospholipid class label distribution of both of these transport phases at various times following precursor injection.
