Axonal transport of glycerophospholipids following intracerebral injection of glycerol into substantia nigra or lateral geniculate body
[2-3H]Glycerol was injected into one substantia nigra of adult rats. Incorporation of radioactivity into lipids at the injection site was maximal by 2 hr, after which it declined. Rapidly transported3H-labeled lipids were just beginning to accumulate in the primary projection site, the ipsilateral corpus striatum by 2 hr, as evidenced by 20-fold higher levels of lipid radioactivity in the projection site relative to control regions. However, the bulk of labeled lipid arrived between 6 hr and 3 days postinjection, suggesting either a prolonged period of release of rapidly transported lipids from the nerve cell bodies or a slow rate of transport for the later arriving lipids. Colchicine applied locally to the fibers of this tract blocked the axonal transport of lipids to the striatum almost completely. Choline and ethanolamine phosphoglycerides were the major transported lipids, accounting for approximately 60% and 25%, respectively, of the total. Similar results were obtained in studies of [2-3H]glycerol-labeled lipids synthesized in the lateral geniculate body and transported to the visual cortex. The rapid axonal transport of lipids labeled with [32P]phosphate (injected simultaneously with [2-3H]glycerol) could also be demonstrated in both tracts. However, in contrast to [2-3H]glycerol, considerable amounts of32P soluble label were present in the projection sites, and colchicine only partially blocked the accumulation of32P-labeled lipid. These results demonstrate the relative utility of [2-3H]glycerol as a lipid precursor for examination of axonal transport in intrabrain tracts. Characteristics of lipid axonal transport in these two intrabrain tracts are similar to each other and are also similar to those previously described for retinal ganglion cells, indicating a common requirement for the axonal transport of these membrane constituents to axons and nerve endings in widely divergent CNS tracts.
KeywordsLipid Colchicine Ethanolamine Retinal Ganglion Cell Axonal Transport
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