ALTERED GAP-43 IMMUNOREACTIVITY IN REGENERATING SCIATIC-NERVE OF DIABETIC RATS

Experimental diabetes in the rat is associated with impaired axon rege neration. Successful regeneration depends on the construction of axona l growth cones and establishment of appropriate target connections. Th e growth-associated protein (GAP)-43 is a major component of the axona l growth cone, and its synthesis and axonal transport are markedly inc reased during regeneration. The purpose of this study was to determine the effect of experimental diabetes on the synthesis and axonal trans port of GAP-43 in regenerating sciatic nerves. Rats were rendered diab etic with 50 mg/kg streptozotocin i.p. Four weeks later, the rats were anesthetized, and one sciatic nerve was crushed to induce regeneratio n. After 2 weeks, nerves were Ligated, and 6 h later, nerve pieces pro ximal to the ligature and dorsal root ganglia were removed, and protei ns were separated by PAGE. Western blots of gels were probed with anti body 10E8/E7 against GAP-43. The presence of GAP-43 was confirmed by i mmunohistochemistry of nerve sections, Densitometric analysis of the b lots showed a 45% reduction in native GAP-43 immunoreactivity in nerve pieces proximal to the ligature (P < 0.05; n = 7). Northern blots of total RNA extracted hom pooled dorsal root ganglia were probed with a P-32-radiolabeled cDNA probe for GAP-43. There was no significant diff erence in the amount of GAP-43 mRNA between diabetic and nondiabetic r ats. Immunohistochemistry of sciatic nerve confirmed the reduction in GAP-43 immunoreactivity. We conclude that a defect in turnover or axon al transport of GAP-43 may contribute to the impaired peripheral nerve regeneration in diabetes.