Distribution of transganglionically labelled soybean agglutinin primary afferent fibres after nerve injury

The distribution of the retrogradely-transganglionically transported lectin soybean agglutinin (SBA) and of SBA conjugated to horseradish peroxidase (SBA-HRP) has been examined in the L_4-5 dorsal root ganglia, lumbar spinal cord and gracile nucleus at 2, 6 and 14 weeks after sciatic nerve transection and ligation. Cell size analysis showed there were no changes in the mean area of labelled DRG profiles after injury. In the spinal cord, terminal labelling was restricted to laminae I and II with no evidence of labelling in novel territories such as the deeper laminae after injury. At 2 weeks, the labelling on the injured side was similar in distribution and intensity to that of the contralateral, uninjured side. At 6-14 weeks the labelling on the injured side was significantly weaker as compared to the contralateral side, but not completely depleted. In the gracile nucleus, at all survival times, an increased distribution and amount of labelling was seen which may reflect sprouting of C and A-delta fibres. These results suggest that SBA is a useful tracer to study the effects of nerve injury on the central terminals of axotomised afferents terminating in laminae I-II and that C-fibres appear not to sprout outside their normal laminar distribution in the dorsal horn after injury.