LOCALLY SYNTHESIZED PHOSPHATIDYLCHOLINE, BUT NOT PROTEIN, UNDERGOES RAPID RETROGRADE AXONAL-TRANSPORT IN THE RAT SCIATIC-NERVE

Retrograde axonal transport of phosphatidylcholine in the sciatic nerv e has been demonstrated only after injection of lipid precursors into the cell body region. We now report, however, that after microinjectio n (1 mul) of [methyl-H-3]choline chloride into the rat sciatic nerve ( 3540 mm distal to the L4 and L5 dorsal root ganglia), time-dependent a ccumulation of H-3-labeled material occurred in dorsal root ganglia ip silateral, but not contralateral, to the injection site. The level of radioactivity in the ipsilateral dorsal root ganglia was minimal at 2 h after isotope injection but was significantly increased at 7, 24, 48 , and 72 h after intraneural isotope injection (n = 3-8 per time point ); at these time points, all of the radiolabel in the chloroform/metha nol extract of the ipsilateral dorsal root ganglia was present in phos phatidylcholine. The radioactivity in the water-soluble fraction did n ot show a time-dependent accumulation in the ipsilateral dorsal root g anglia as compared with the contralateral DRGs, ruling out transport o r diffusion of precursor molecules. In addition, colchicine injection into the sciatic nerve proximal to the isotope injection site prevente d the accumulation of radiolabel in the ipsilateral dorsal root gangli a. Therefore, this time-dependent accumulation of radiolabeled phospha tidylcholine in the ipsilateral dorsal root ganglia is most likely due to retrograde axonal transport of locally synthesized phospholipid ma terial. Moreover, 24 h after injection of both [H-3]choline and [S-35] methionine into the sciatic nerve, the ipsilateral/contralateral ratio of radiolabel was 11.7 for H-3 but only 1.1 for S-35, indicating that only locally synthesized choline phospholipids, but not protein, were retrogradely transported.