Molecular and neuroanatomical properties of the endogenous opioid system: Implications for treatment of opiate addiction

This review describes the emergence of the opioid field, in terms of both endogenous peptides and their receptors. It discusses the basic elements of the opioid system with special attention to the way a large number of endogenous ligands interact with a limited number of opioid receptors. The contribution of the recent cloning of the opioid receptors to our understanding of the system is discussed, including the mechanisms of high affinity and selectivity for endogenous and exogenous ligands, and the mechanisms of signal transduction following acute and sustained exposure to opiates. The expression of opioid receptors and ligands in dopaminoceptive systems relevant to drug reward is described. Finally, the implications of these fundamental observations for new directions in drug abuse research are discussed.