NGF was discovered 50 years ago as a molecule that promoted the survival and differentiation of sensory and sympathetic neurons.
Its roles in neural development have been characterized extensively, but recent findings point to an unexpected diversity of NGF actions, indicating that developmental effects are only one aspect of the biology of NGF.
NGF has expanded roles associated with the dynamically regulated production of NGF and its receptors that begins in development, extends throughout adult life and aging, and involves a surprising variety of neurons, glia, and non-neural cells.
There is a growing body of evidence that suggests that, among other roles, endogenous NGF signaling subserves neuroprotective and repair functions.

Sofroniew MV, Howe CL, Mobley WC. Nerve growth factor signaling, neuroprotection, and neural repair. Annu Rev Neurosci. 2001;24:1217-81.