Purification of a neurite growth inhibitor (NI-250) from bovine CNS myelin

In the central nervous system (CNS) the ability of nerve fibres to regenerate upon injury is very limited. In contrast, peripheral nerve fibres have been observed to regrow over long distances. Transplantation experiments with CNS and PNS nerve explants have shown that the local microenvironment is crucial for regenerating nerve fibers: CNS neurons can extend their lesioned neurites into the peripheral nerve environment, but cease growth at the transition between PNS and CNS (Aguayo et al 1990; David and Aguayo 1981; Ramon y Cajal 1928; Tello 1911). To test if a possible lack of trophic factors in the adult CNS might be responsible for this observation, perinatal rat sensory, sympathetic, or retinal neurons were cocultured with explants of adult rat sciatic (PNS) or optic nerves (CNS) in the presence of nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF) (Schwab & Thoenen 1985). The pattern of fiber growth corresponded exactly to that found in vivo: many axons grew into the sciatic nerve explants, but none grew into the optic nerves. These results suggested that there is a neurite growth inhibitory activity present in adult CNS tissue that cannot be overcome by the stimulatory effects of neurotrophic factors (Schwab & Thoenen, 1985).