Retrograde support of neuronal survival without retrograde transport of nerve growth factor.

Application of nerve growth factor (NGF) covalently cross-linked to beads increased the phosphorylation of TrkA and Akt, but not of mitogen-activated protein kinase, in cultured rat sympathetic neurons. NGF beads or iodine-125-labeled NGF beads supplied to distal axons resulted in the survival of over 80% of the neurons for 30 hours, with little or no retrograde transport of iodine-125-labeled NGF; whereas application of free iodine-125-labeled NGF (0.5 nanograms per milliliter) produced 20-fold more retrograde transport, but only 29% of the neurons survived. Thus, in contrast to widely accepted theory, a neuronal survival signal can reach the cell bodies unaccompanied by the NGF that initiated it.