In Brief:
Transplantation of neural progenitor cells promoted axon growth from the brain cortex into the spinal cord in organotypic cocultures. In addition, the axon growth promoted by NPCs was significantly suppressed by the addition of neutralizing antibodies against BDNF, NT-3, and NGF. These findings suggest that BDNF, NT-3, and NGF secreted by transplanted NPCs are involved in the promotion of corticospinal axon growth after transplantation of NPCs.