The ND7/23 cells, deriving from a hybridoma of neonatal rat DRG neurons and N18TG2 mouse neuroblastoma cells, possess a high proliferative activity with some characteristic features of sensory neurons (e.g., expression of substance P and the neurotrophin receptor, TrkA; formaldehyde-induced increases in intracellular Ca2+; and prostaglandin E2-induced neurite outgrowth via the second messenger, cAMP) [17,18]. This evidence concerns the gene NTRK1 and neuroblastoma.