BASIC FIBROBLAST GROWTH-FACTOR PROMOTES EXTENSION OF REGENERATING AXONS OF PERIPHERAL-NERVE - IN-VIVO EXPERIMENTS USING A SCHWANN-CELL BASAL LAMINA TUBE MODEL

Schwann cell basal lamina tubes serve as attractive conduits for regen eration of peripheral nerve axons. In the present study, by using basa l lamina tubes prepared by in situ freeze-treatment of rat saphenous n erve, the effects of exogenously applied basic fibroblast growth facto r (bFGF) on peripheral nerve regeneration was examined 2 and 5 days af ter bFGF administration. Regenerating axons were observed by light and electron microscopy using PGP9.5-immunohistochemistry for specific st aining of axons. In addition, the localizations of bFGF and its recept or (FGF receptor-1) were examined by immunohistochemistry using anti-b FGF antibody and anti-FGF receptor-1 antibody, respectively. Regenerat ing axons extended further in the bFGF-administered segment than in th e bFGF-untreated control segment. Electron microscopy showed that rege nerating axons grew out unaccompanied by Schwann cells. Findings conce rning angiogenesis and Schwann cell migration were very similar betwee n the bFGF treated and control nerve segment. bFGF-immunoreactivity wa s not detected in the control nerve segment. In contrast, bFGF-immunor eactivity was detected on the basal lamina tubes as well as on the pla smalemma of regenerating axons facing the basal lamina in the bFGF tre ated nerve segment up to 5 days after administration, suggesting that exogenous bFGF can be retained in the basal lamina for several days af ter administration. FGF receptor was detected on the plasma membrane o f regenerating axons where they abutted the basal lamina. These result s indicate that bFGF could promote the extension of early regenerating axons by directly influencing the axons, but not via Schwann cells or angiogenesis.