ULTRASTRUCTURAL-LOCALIZATION OF SYMPATHETIC AXONS IN EXPERIMENTAL RATSCIATIC-NERVE NEUROMAS

The ultrastructural localization of sympathetic axons was investigated in normal rat sciatic nerves and experimental sciatic nerve neuromas. The best ultrastructural localization of noradrenaline in the dense-c ored vesicles of sympathetic axons was accomplished following pretreat ment of rats with nialamide and 5-hydroxy dopamine, followed by fixati on according to the modified chromaffin technique of Tranzer and Richa rds (1976). After such preparation, sympathetic axons containing 5-hyd roxy dopamine-labelled dense-cored vesicles could be identified in nor mal sciatic nerve. Large accumulations of labelled dense-cored vesicle s were also found in acute neuromas, up to 1 week after nerve section. Much smaller numbers of dense-cored vesicles could be identified in c hronic neuromas from 2 to 3 weeks following nerve section. Sympathetic axons could also be identified following electron probe X-ray microan alysis of the tissue sections, using chromium detection as the marker for the noradrenaline-containing dense-cored vesicles. Unusual configu rations of Schwann cell subunits, which enclosed myelinated fibres and sympathetic axon sprouts within the same basal lamina, were identifie d in the acute neuromas, 3-7 days after nerve section. Such configurat ions may be of relevance to the pathophysiological interaction which d evelops between sympathetic efferent and sensory fibres in peripheral nerve neuromas.