Diversity of the endogenous opioid system in development - Novel signal transduction translates multiple extracellular signals into neural cell growth and differentiation

This review explores the role of individual opioid receptor types and signa l transduction pathways on cell growth and differentiation. The findings re viewed herein provide suggestive evidence that while no single opioid recep tor or peptide type exclusively regulates growth, depending on the cell typ e, the activation of all three (mu, delta, or kappa) opioid receptor types can affect maturation in a cell type-dependent manner. Specific development al responses are determined primarily by how a particular opioid receptor t ype is coupled to intracellular signaling effecters. Moreover, the coupling of opioid receptors appears to be developmentally regulated, and these pro tein-protein interactions change during ontogeny. The diversity of opioid r eceptor types and intracellular effecters may be a mechanism by which indiv idual cells discriminate among different opioid signals, and may permit div erse opioid signals to be translated into a unique developmental logic in d istinct neuronal and glial subpopulations.