ABSTRACT
Opioid analgesic drugs and endogenous opioid peptides exert a wide spectrum of physiological and behavioral effects on pain perception, mood, motor control, and autonomic function. The myriad opioid-induced effects are mediated via a family of the specific membrane-bound receptor located on nervous tissue, namely the opioid receptor. Early studies of the bindings of various ligands have suggested the existence of a multitude of distinct types of opioid receptors that can interact with opioid drugs or endogenous peptides. More evidence for the existence of opioid receptor types has recently been confirmed by molecular cloning. The three major opioid receptor types-mu, delta, and kappa-have been cloned and sequenced [1-12].
