This invention provides a method for regulating migration of neuronal progenitor cells in the nervous system of a mammal. The method comprises providing a mammal with TNR, a biologically active fragment of TNR, or a TNR agonist in an amount sufficient to direct migration of the neuronal progenitor cells. The invention provides a method of treating neurological diseases by replenishing diseased, damaged, or destroyed neural cells in the central nervous system or in the peripheral nervous system.