Opioid Peptides

Abstract

Since the discovery of opioid receptors and their endogenous ligands named opioid peptides, it has been established that opiates exert their effects by mimicking effects of three endogenous opioid peptide families (the enkephalins, the endorphins, and the dynorphins). Over last three decades, great advance has been made in understanding the basic physiology of endogenous opioid peptide (EOP) systems and their biogenesis, anatomy, and functions. EOPs and their receptors are expressed in the CNS, the periphery, the gut, and the immune system. The EOPs act as transmitters or modulate synaptic actions of primary transmitters. There are numerous data implicating EOPs in the central and peripheral antinociception, motor activity, feeding, sexual behavior, regulation of body temperature respiration, as well as cardiovascular and gastrointestinal functions. They are known to be released from endocrine organs and are involved in regulation of release of various hormones and modulation of immune functions. EOPs are involved in reward, learning and memory, and emotional states. EOP systems play an important role in modulation and adaptation of the organism to challenges. While relatively quiescent in the resting state, EOPs are released during intense stimulation and modify disturbed homeostasis. EOPs appear to be involved in brain diseases such as pain, addiction, depression, and anxiety disorders. Progress made during the last years in pharmacology, genomics, and complex genetics opens avenues for investigating a role of the EOPs and their receptors in various brain diseases and new pathways for investigating novel opioid therapeutics.