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Papers of the Week

Papers: 20 Jan 2024 - 26 Jan 2024

2024 Jan 06



Negative allosteric modulation of cannabinoid CB1 receptor signaling suppresses opioid-mediated tolerance and withdrawal without blocking opioid antinociception.


Iyer V, Saberi SA, Pacheco R, Sizemore EF, Stockman S, Kulkarni A, Cantwell L, Thakur GA, Hohmann AG


The direct blockade of CB cannabinoid receptors produces therapeutic effects as well as adverse side-effects that limit their clinical potential. CB negative allosteric modulators (NAMs) represent an indirect approach to decrease the affinity and/or efficacy of orthosteric cannabinoid ligands or endocannabinoids at CB . We recently reported that GAT358, a CB -NAM, blocked opioid-induced mesocorticolimbic dopamine release and reward via a CB -allosteric mechanism of action. Whether a CB -NAM dampens opioid-mediated therapeutic effects such as analgesia or alters other unwanted side-effects of opioids remain unknown. Here, we characterized the effects of GAT358 on nociceptive behaviors in the presence and absence of morphine. We examined the impact of GAT358 on formalin-evoked pain behavior and Fos protein expression, a marker of neuronal activation, in the lumbar dorsal horn. We also assessed the impact of GAT358 on morphine-induced slowing of colonic transit, tolerance, and withdrawal behaviors. GAT358 attenuated morphine antinociceptive tolerance without blocking acute antinociception. GAT358 also reduced morphine-induced slowing of colonic motility without impacting fecal boli production. GAT358 produced antinociception in the presence and absence of morphine in the formalin model of inflammatory nociception and reduced the number of formalin-evoked Fos protein-like immunoreactive cells in the lumbar spinal dorsal horn. Finally, GAT358 mitigated the somatic signs of naloxone-precipitated, but not spontaneous, opioid withdrawal following chronic morphine dosing in mice. Our results support the therapeutic potential of CB -NAMs as novel drug candidates aimed at preserving opioid-mediated analgesia while preventing their unwanted side-effects. Our studies also uncover previously unrecognized antinociceptive properties associated with an arrestin-biased CB -NAMs.