Neuropilin-1 on the growth cones of NGF-dependent embryonic dorsal root ganglion (DRG) neurons mediates the repulsive effects of secreted semaphorin3a, but its role in adult neurons is unknown. Here we show that most adult rat DRG neurons, regardless of cell diameter/afferent phenotype, express neuropilin-1 protein in vitro. However, the response of growth cones belonging to these neurons (induced by recombinant collapsin-1/semaphorin3a and blocked by the anti-neuropilin-1 antibody) was restricted to those of small cell body diameter (<30 microm), corresponding primarily to nociceptive sensory afferents. Neurotrophic factors had a differential effect on neuropilin-1 expression in vitro, with DRG neurons cultured in either NGF or GDNF expressing the highest levels on their neurites. These findings suggest that neuropilin-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.