The short term accumulation of axonally transported organelles in the region of localized lesions of single myelinated axons.

Myelinated axons were isolated from the sciatic nerve of Xenopus laevis and were subjected to localized (less than 30 microns wide) lesions. In axons which were bathed in a 0.12 M potassium glutamate solution there was very little local reaction to the lesion and optically-detectable particles undergoing axoplasmic transport accumulated immediately adjacent to, and mostly distal to, the lesion. Preparations fixed for electron microscopy at times up to 3 h following the lesion showed that the axoplasmic changes about the lesion were asymmetrical. Large organelles predominated on the distal side of the lesion; these were mostly dense lamellar bodies (DLB) with mean dimensions, as determined from thin sections, of 0.48 by 0.19 microns. Multivesicular bodies, mitochondria, and a variety of smaller membrane bounded bodies also appeared in the particle accumulation distal to the lesion. Analysis of these results led to the conclusion that DLB were transported up to the lesion and represent the majority of the optically detectable particles which are transported in the retrograde direction. Small vesicles and tubules were the commonest structures which accumulated proximal to the lesion. The time course of this accumulation was consistent with the hypothesis that these structures are particulate bodies which move in the orthograde direction at about 1.5 microns/s. Incidental findings which are also of significance to the study of axonal transport were: large particulate material may reverse its direction of movement at an axonal obstruction, and organelles which accumulate on either side of a lesion do so in rows which are associated with microtubules.