Retrograde transport of nerve growth factor (NGF) in motoneurons of developing rats: assessment of potential neurotrophic effects.

The potential functional significance of nerve growth factor (NGF) receptors in spinal motoneurons was studied in newborn rats. 125I-NGF was specifically retrogradely transported by motoneurons from their peripheral nerve terminals. This transport was blocked by an excess of unlabeled NGF but not by cytochrome c. 125I-cytochrome c was not transported. The monoclonal anti-rat NGF receptor antibody, but not a control antibody, was also transported. Despite this ability of motoneurons to transport NGF, treatment of newborn rats with this factor did not increase motoneuron size or synthesis of neurotransmitter enzymes and did not prevent cell death after axotomy. We conclude that NGF receptors of spinal motoneurons can bind, internalize, and retrogradely transport NGF. However, these receptors do not mediate the classic trophic effects of NGF.