Neuropilin-1 is expressed on adult mammalian dorsal root ganglion neurons and mediates Semaphorin3a/collapsin-1-induced growth cone collapse by smalldiameter sensory afferents

Neuropilin-1 on the growth cones of NGF-dependent embryonic dorsal root gan glion (DRG) neurons mediates the repulsive effects of secreted semaphorin3a , but its role in adult neurons is unknown. Here we show that most adult ra t DRG neurons, regardless of cell diameter/afferent phenotype, express neur opilin-1 protein in vitro. However, the response of growth cones belonging to these neurons (induced by recombinant collapsin-1/semaphorin3a and block ed by the anti-neuropilin-1 antibody) was restricted to those of small cell body diameter(<30 mu m), corresponding primarily to nociceptive sensory af ferents. Neurotrophic factors had a differential effect on neuropilin-1 exp ression in vitro,with DRG neurons cultured in either NGF or GDNF expressing the highest levels on their neurites. These findings suggest that neuropil in-1-mediated repellent effects of semaphorins may regulate the behavior of nociceptive sensory axons in the adult as well as the embryonic peripheral nervous system.