Influence of peripheral inflammation on growth-associated phosphoprotein (GAP-43) expression in dorsal root ganglia and on nerve recovery after crush injury

An experimental study was performed to investigate the influence of the inflammation in peripheral target tissue on growth-associated phosphoprotein (GAP-43) expression in dorsal root ganglia (DRG) and on recovery of crushed nerve. Fifty-four male Wistar rats were used for this study. The sciatic nerve was operatively crushed unilaterally with an aneurysm clip. Inflammation in peripheral target tissue was induced by injection of complete Freund's adjuvant (CFA) at 1 week before crush. In crushed or crushed with arthritis rats DRGs were examined in immunohistochemistry for GAP-43 and the sciatic nerves were observed in Epon embedded sections with toluidine blue stain. In addition, electrophysiological studies of the nerves were performed to evaluate the recovery of function. Immunohistochemical studies showed the ratio of GAP-43 immunopositive cells in crushed with arthritis rats was significantly lower than that in crushed rats at 1 week after crush (P<0.01). Electrophysiological studies at 4 weeks after crush showed functional nerve recovery in crushed with arthritis rats was significantly suppressed compared with that in crushed rats (P<0.01). Histological studies showed the mean diameter of the axons in crushed with arthritis rats was significantly smaller than that in crushed rats (P<0.01). All these findings indicate that inflammation in peripheral target tissue suppresses GAP-43 expression in DRG and eventually suppresses functional and morphological recovery of the crushed nerve.