British journal of pharmacology
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The morbidity and mortality associated with recreational use of synthetic cannabinoid receptor agonists (SCRAs) may reflect strong activation of CB1 receptors and is a major health concern. The properties of SCRA at CB1 receptors are not well defined. Here we have developed an assay to determine acute CB1 receptor efficacy using receptor depletion with the irreversible CB1 receptor antagonist AM6544, with application of the Black and Leff operational model to calculate efficacy. ⋯ All SCRAs tested showed substantially higher efficacy at CB1 receptors than ∆9 -THC, which may contribute to the adverse effects seen with these drugs but not ∆9 -THC.
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The concept of opioid ligands biased towards the G protein pathway with minimal recruitment of β-arrestin-2 is a promising approach for the development of novel, efficient, and potentially nonaddictive opioid therapeutics. A recently discovered biased μ-opioid receptor agonist, PZM21, showed analgesic effects with reduced side effects. Here, we aimed to further investigate the behavioural and biochemical properties of PZM21. ⋯ PZM21 exhibited antinociceptive efficacy, without rewarding or reinforcing properties. However, its clinical application may be restricted, as it induces tolerance and withdrawal symptoms. Notably, its ability to diminish morphine reward implies that PZM21 may be useful in treatment of opioid use disorders.