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.