Effects of nerve growth factor on cultured adult dorsal root ganglion neurons evaluated by enzyme immunoassay for neurofilament protein

Abstract

We examined the effects of nerve growth factor (NGF) on cultured dorsal root ganglion (DRG) neurons obtained from 10-, 72-and 114-week-old mice by using a newly developed enzyme immunoassay (EIA) for neurofilament protein. Neurofilament protein levels estimated with EIA were demonstrated to depend on neurite length as well as on the neuronal number. Neurofilament protein levels increased with increasing NGF added, while surviving neuronal numbers were not affected by NGF. This indicates that NGF accelerated neurite elongation, but was not required for survival of adult DRG neurons. We also revealed that neurite-extending capacity dependent on NGF was reduced with aging, but a large amount of NGF significantly stimulated neurite extension even in 114-week old mice. Accordingly, diminished neurite regeneration after damage to neural tissue of aged animals may be related in part to a reduction of growth-inducing substances such as NGF possibly secreted by target cells as well as a reduction in the ability of neurons to synthesize or to assemble materials necessary for repair.