Molecular pharmacology of the opioid receptors

Opioid receptors are the primary sites of actions of opiates and endogenous opioid peptides, which have a wide variety of pharmacological and physiological effects. The opioid receptors are classified into at least three subtypes, mu, delta, and x, and their cDNAs have been cloned. In this review, we describe the molecular cloning of opioid receptor gene family and studies of the structure-function relationships, modes of coupling to second messenger systems, pharmacological effects of antisense oligonucleotides, and anatomical distribution of opioid receptor mRNAs.