Microtubule-mitochondrial associations in regenerating axons after taxol intoxication.

Ultrastructural examination of regenerating axons within rat sciatic nerve injected locally with the microtubule assembly-promoting compound, taxol, has revealed the frequent association of microtubules with axoplasmic organelles, in particular mitochondria. This was characterized by the prodigious accumulation of axonal microtubules, some of which became aligned to form multilayered channels within which axoplasmic organelles were sequestered. Between each layer of microtubules forming the walls of these channels, a 5 nm filament, believed to derive from microtubule side-arm material, was present. The findings suggest that these microtubule channels might play a role in mitochondrial traffic across the lesion area. Similar but much less elaborate associations within axons between microtubules and axoplasmic organelles, including mitochondria, have been described previously. Within regenerating axonal sprouts, intermediate filaments were found only at later timepoints when they commonly occurred within the microtubule channels. It is proposed that taxol impedes axonal regrowth at an early stage of cytoskeleton formation and that that the present observations represent drug-induced exaggerations of a normal phenomenon.