Heterodimerization of opioid receptor-like 1 and mu-opioid receptors impairs the potency of micro receptor agonist

Endogenous opiates and behavior: 2005

This paper is the 28th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2005 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity, neurophysiology and transmitter release (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); immunological responses (Section 17).

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Two C-terminal amino acids, Ser(334) and Ser(335), are required for homologous desensitization and agonist-induced phosphorylation of opioid receptor-like 1 receptors

Various cellular signaling pathways induced by nociceptin activation of ORL1 (opioid receptor-like 1 receptor) develop homologous desensitization. Multiple lines of evidence suggest that agonist-induced phosphorylation of serine (Ser)/threonine (Thr) residues at intracellular carboxyl tail leads to homologous desensitization of G protein-coupled receptors. In the present study, we investigated the functional role played by C-terminal Ser/Thr residues in agonist-induced desensitization and phosphorylation of ORL1. In HEK 293 cells expressing wild-type ORL1 and ORL1(CDelta21), which lacks C-terminal 21 amino acids, nociceptin inhibition of adenylate cyclase activity exhibited homologous desensitization after 1 h pretreatment of nociceptin. In contrast, ORL1(CDelta34), which differs with ORL1(CDelta21) by lacking C-terminal Ser(334), Ser(335) and Ser(343) residues, failed to develop agonist-induced desensitization. Point mutant (S343A) ORL1 underwent homologous desensitization after nociceptin pretreatment. Substituting Ser(334) or Ser(335) with alanine greatly impaired nociceptin-induced ORL1 desensitization. In HEK 293 cells expressing double mutant (S334A/S335A) ORL1, nociceptin pretreatment failed to significantly affect the efficacy and potency by which nociceptin inhibits forskolin-stimulated cAMP formation. Mutation of Ser(334) and Ser(335) also greatly reduced nociceptin-induced ORL1 phosphorylation. These results suggest that two C-terminal serine residues, Ser(334) and Ser(335), are required for homologous desensitization and agonist-induced phosphorylation of ORL1.