Regenerative repair in the severed optic nerve of the newt ( Triturus viridescens): Effect of nerve growth factor

Abstract

Nerve growth factor had a strong stimulatory effect on the regenerative capacity of the transected newt ( Triturus viridescens) optic nerve. A clear dose-response relationship was demonstrated between various concentrations of single intraocular nerve growth factor injections, administered at the time of lesion, and the number of regenerating axons per nerve cross section at 14 days postlesion. A rapid rise in numbers of regenerating axons was evident in animals treated with nerve growth factor concentrations of 2 to 20 biological units (BU) but values plateaued between 20 and 2000 BU. Light microscopic observations indicated that nerve growth factor-treated nerves were larger than controls. Quantitative analysis substantiated these initial observations by revealing that a single intraocular injection of 200 BU given at the time of lesion elicited a highly significant increase in both diameters and cross-sectional areas of regenerating nerves 14 days after lesion. Most importantly, nerve growth factor treatment elicited approximately a two-fold increase in the total number of regenerating axons per nerve cross section. In addition, the percentage of nerve cross-sectional area occupied by regenerating axons was significantly increased by this treatment. However, the percentage of glial cytoplasm per cross-sectional area remained constant for both control and experimental groups.