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Hoffmann, R. A wiki for the life sciences where authorship matters. Nature Genetics (2008)

Activity of the delta-opioid receptor is partially reduced, whereas activity of the kappa-receptor is maintained in mice lacking the mu-receptor.

Previous pharmacological studies have indicated the possible existence of functional interactions between mu-, delta- and kappa-opioid receptors in the CNS. We have investigated this issue using a genetic approach. Here we describe in vitro and in vivo functional activity of delta- and kappa-opioid receptors in mice lacking the mu-opioid receptor ( MOR). Measurements of agonist-induced [35S]GTPgammaS binding and adenylyl cyclase inhibition showed that functional coupling of delta- and kappa-receptors to G-proteins is preserved in the brain of mutant mice. In the mouse vas deferens bioassay, deltorphin II and cyclic[D-penicillamine2, D-penicillamine5] enkephalin exhibited similar potency to inhibit smooth muscle contraction in both wild-type and MOR -/- mice. delta-Analgesia induced by deltorphin II was slightly diminished in mutant mice, when the tail flick test was used. Deltorphin II strongly reduced the respiratory frequency in wild-type mice but not in MOR -/- mice. Analgesic and respiratory responses produced by the selective kappa-agonist U-50,488H were unchanged in MOR-deficient mice. In conclusion, the preservation of delta- and kappa-receptor signaling properties in mice lacking mu-receptors provides no evidence for opioid receptor cross-talk at the cellular level. Intact antinociceptive and respiratory responses to the kappa-agonist further suggest that the kappa-receptor mainly acts independently from the mu-receptor in vivo. Reduced delta-analgesia and the absence of delta-respiratory depression in MOR-deficient mice together indicate that functional interactions may take place between mu-receptors and central delta-receptors in specific neuronal pathways.[1]


  1. Activity of the delta-opioid receptor is partially reduced, whereas activity of the kappa-receptor is maintained in mice lacking the mu-receptor. Matthes, H.W., Smadja, C., Valverde, O., Vonesch, J.L., Foutz, A.S., Boudinot, E., Denavit-Saubié, M., Severini, C., Negri, L., Roques, B.P., Maldonado, R., Kieffer, B.L. J. Neurosci. (1998) [Pubmed]
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