Molecular mechanisms of opioid receptor signal transduction

key experiments have resulted in extensive pharmacological characterization of opioid receptors, the presence of heterologous receptor populations and low expression in cells have always hampered further receptor studies. Recent cloning of the , and opioid receptors 16 27 49 117 has allowed many quest ions to be answered by expressing receptor cDNAs in cell lines that lack endogenous receptors. While these studies have yielded invaluable data on receptor structure, the molecular nature of desensitization remains largely unresolved. A connection between cellular desensitization and drug tolerance has led countless scientists to puzzle over the molecular mechanisms controlling cellular adaptation. The long-term effect of agonists on the molecular mechanisms of signal transduction are important in understanding tolerance.