EFFECTS OF NERVE CONSTRICTION ON OXYGENATED EXCISED SEGMENTS OF RAT PERIPHERAL NERVE

Abstract

The accumulations of axoplasmic components proximal and distal to constrictions of peripheral nerves were studied in excised, oxygenated segments of rat sciatic nerve and compared with similar phenomena occurring adjacent to in situ constrictions along the same nerve. Excised nerve preparations were incubated in dextrose-enriched Ringer's solution at 37°C under 95% O₂ and 5% CO₂ for intervals up to 8 hours. The proximal and distal edges of the in situ and excised constricted nerves were processed for serial ultrastructural examination. Distributions of succinic dehydrogenase and acetyl cholinesterase activities within the constricted nerve fibers were studied by whole-mount histochemical procedures. Progressive accumulations of axoplasmic organelles and enzymatic activity were noted in the excised nerve segments adjacent to the constrictions. These accumulations were indistinguishable from those occurring at in situ constrictions. Accumulations in unmyelinated fibers were located immediately adjacent to the constrictive sites while axonal accumulations of myelinated fibers were separated from the constrictive site by a 200–800µ segment of disorganized nerve fiber. Predominant accumulations were always seen on the proximal edge of the constrictive site. Some myelinated nerve fibers of in situ and excised constricted nerve, however, failed to show enzymatic accumulation in the proximal and/or distal segments. The demonstration of axonal accumulations adjacent to constrictions in oxygenated excised segments of peripheral nerve indicates the indigenous nature of this phenomenon and offers a model system for further study of the underlying cellular mechanisms.