MODULATION OF CHEMOTROPISM IN THE DEVELOPING SPINAL-CORD BY SUBSTANCE-P

Developing axons find their targets through direct contact with cues i n the extracellular environment and in response to gradients of diffus ible factors. The floor plate, a neuroepithelial structure, guides dev eloping commissural axons in the spinal cord by release of chemoattrac tants. Floor plate cells express neurokinin-1 receptors, and a transie ntly 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 fl oor plate explants. Results of experiments with embryonic rats suggest that substance P released from pioneering neuronal pathways may regul ate the release of chemoattractants from floor plate cells.