ELEVATED INSULIN-LIKE GROWTH-FACTOR (IGF) GENE-EXPRESSION IN SCIATIC-NERVES DURING IGF-SUPPORTED NERVE REGENERATION

Nerve regeneration is augmented by neurotrophic activity, which has lo ng been known to be increased in lesioned nerves. Of identified solubl e nerve-derived neurotrophic factors, to date only insulin-like growth factors (IGFs) have been observed to increase the rate of axon regene ration in peripheral nerves. We report that IGF-I and IGF-II mRNA cont ents were significantly increased (P < 0.0005) distal to the site of c rush in rat sciatic nerves, and decreased following axon regeneration. In transected nerves in which axon regeneration was prevented, IGF mR NAs remained elevated. IGF-I mRNAs per mg tissue were increased more i n lesioned nerves than denervated muscles, whereas IGF-II mRNAs were i ncreased more in denervated muscles than lesioned nerves. This suggest ed that IGF-I and IGF-II each play distinct regulatory roles during re generation, These data bolster the hypothesis that increased IGF mRNA content in nerves supports the rate of nerve regeneration in mammals.