Modulation of chemotropism in the developing spinal cord by substance P

Developing axons find their targets through direct contact with cues in the extracellular environment and in response to gradients of diffusible factors. The floor plate, a neuroepithelial structure, guides developing commissural axons in the spinal cord by release of chemoattractants. Floor plate cells express neurokinin-1 receptors, and a transiently appearing subpopulation of commissural axons contains substance P, the neuropeptide ligand for this receptor. Substance P increases the amount of axon outgrowth from dorsal horn explants cocultured with floor plate explants. Results of experiments with embryonic rats suggest that substance P released from pioneering neuronal pathways may regulate the release of chemoattractants from floor plate cells.