A fluorescence study of changes in noradrenergic sympathetic fibres in experimental peripheral nerve neuromas

Experimental neuromas were produced in rats by sciatic nerve section and avulsion of the distal stumps. At intervals varying from 3 days to 8 weeks after nerve section, the developing neuromas were resected and processed for noradrenaline (NA) fluorescence microscopy by the sucrose-phosphate-glyoxylic acid (SPG) method. From serial longitudinal sections through the neuromas and the nerve proximally, counts of noradrenergic sympathetic axons were made, together with qualitative observations of axon sprouting and NA content. By 3 days after nerve section there was a massive sprouting of sympathetic axons, with increased NA content, particularly towards the distal tip of the neuroma. Axon counts remained high 1 week following section then fell to below normal levels at 2 weeks, returning towards normal 8 weeks after nerve section. These results are discussed in relation to the known pathophysiological interaction between sympathetic efferent and sensory afferent fibres, which develops in neuromas following nerve section.