2 research outputs found

    βγ G-proteins, but not regulators of G-protein signaling 4, modulate opioid-induced respiratory rate depression

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    Opioid medications are the mainstay of pain management but present substantial side-effects such as respiratory depression which can be lethal with overdose. Most opioid drugs, such as fentanyl, act on opioid receptors such as the G-protein-coupled µ-opioid receptors (MOR). G-protein-coupled receptors activate pertussis toxin-sensitive G-proteins to inhibit neuronal activity. Binding of opioid ligands to MOR and subsequent activation G proteins βγ is modulated by regulator of G-protein signaling (RGS). The roles of G-proteins βγ and RGS in MOR-mediated inhibition of the respiratory network are not known. Using rodent models to pharmacologically modulate G-protein signaling, we aim to determine the roles of βγ G-proteins and RGS4. We showed that inhibition of βγ G-proteins using gallein perfused in the brainstem circuits regulating respiratory depression by opioid drugs results in complete reversal of respiratory depression. Blocking of RGS4 using CCG55014 did not change the respiratory depression induced by MOR activation despite co-expression of RGS4 and MORs in the brainstem. Our results suggest that neuronal inhibition by opioid drugs is mediated by G-proteins, but not by RGS4, which supports the concept that βγ G-proteins could be molecular targets to develop opioid overdose antidotes without the risks of re-narcotization often found with highly potent opioid drugs. On the other hand, RGS4 mediates opioid analgesia, but not respiratory depression, and RGS4 may be molecular targets to develop pain therapies without respiratory liability

    G-protein Signaling Regulating Opioid-induced Respiratory Rate Depression

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    Opioids are pain treatment mainstays, but present with potentially lethal respiratory depression. To develop safer opioid therapies, mechanisms underlying opioid-induced respiratory depression must be better understood. Opioids mainly bind to µ-opioid receptors (MORs), Gprotein-coupled receptors that activate heterotrimeric G-proteins, including Gβγ. There is significant debate around whether G-proteins or β-arrestins, proteins involved in receptor internalization/desensitization, directly regulate respiratory circuit inhibition. While Gβγ activates G-protein inwardly rectifying potassium (GIRK) channels, which are key mediators of respiratory rate depression, its direct role in opioid-induced respiratory depression is unknown. We investigated the contribution of Gβγ in opioid-induced respiratory rate depression and found Gβγ inhibition in respiratory circuits reversed opioid-induced respiratory rate depression, regulators of G-protein signaling 4 (RGS4) are co-expressed with MORs in respiratory circuits, and RGS4 inhibition in vivo potentiates opioid-induced respiratory rate depression. Our data suggest G-protein signaling is key in opioid-induced respiratory depression and is not limited to β-arrestin recruitment.M.Sc
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