Geometric response to nerve growth factor is preserved in aged rat sensory neurons: a single-neuron culture study.

We previously established a single-neuron culture system to analyze the primary effects of neurotrophic factors and reported that NGF promoted neurite extension in young adult (4- to 6-month-old) rat dorsal root ganglion (DRG) neurons by promoting neurite arborization. In this study, we demonstrated that the effects of NGF on neurite regeneration in DRG neurons was well preserved in aged rats (20- to 24-month-old and 33-month-old). NGF did not increase the percent process-bearing neurons in aged rats, which indicated that neuronal survival was not promoted by NGF, but it significantly enhanced the number of branching points, total neurite length, and soma size in aged neurons. These effects of NGF on neurite geometry tended to be reduced to some extent in aged neurons and the initiation of neurite-outgrowth in aged neurons was also delayed as compared with young adult neurons. NGF-responsive subpopulation of neurons, found in the entire range of neuronal size, were preserved in aged rats. These findings indicate that NGF could play an important role in regeneration of injured DRG neurons of aged animals.