Myelin-associated glycoprotein (MAG) is a well-characterized axon growth inhibitor in the adult vertebrate nervous system. Several signals that play roles in inhibiting axon growth have been identified. Here, we report that soluble MAG induces activation of Rap1 in postnatal cerebellar granule neurons (CGNs) and dorsal root ganglion (DRG) neurons. The p75 receptor associates with activated Rap1 and is internalized in response to MAG. After MAG is applied to the distal axons of the sciatic nerves, the activated Rap1, internalized p75 receptor, and MAG are retrogradely trafficked via axons to the cell bodies of the DRG neurons. Rap1 activity is required for survival of the DRG neurons as well as CGNs when treated with MAG. The transport of the signaling complex containing the p75 receptor and Rap1 may play a role in the effect of MAG.