THC required both CB1 and CB2 receptors for its full effects in mice, while the synthetic cannabinoid XLR11 worked through CB1 alone, and GPR55 receptors appeared to oppose cannabinoid effects.
Cannabinoid pharmacologists, researchers developing cannabinoid-based medicines, and scientists studying receptor interactions.
CB2 needed for THC's effects but not for synthetic cannabinoid XLR11
What the researchers found
CB1 deletion abolished tetrad effects for all three cannabinoids. CB2 deletion abolished THC and WIN55,212-2 analgesia and catalepsy but not XLR11's. GPR55 deletion enhanced responses to THC and WIN55,212-2. These findings held for both systemic and central (intraventricular) administration.
Why it matters
The assumption that all cannabinoid effects are mediated solely through CB1 is incomplete. Plant cannabinoids and synthetic cannabinoids may engage different receptor combinations, which has implications for both therapeutic development and understanding synthetic cannabinoid toxicity.
The numbers in context
Three cannabinoids tested across four mouse genotypes. CB2 knockout abolished THC analgesia and catalepsy but not XLR11's. GPR55 knockout enhanced responses to phytocannabinoids. Pharmacological results matched genetic findings.
How the study worked
Compared tetrad effects (analgesia, hypothermia, catalepsy, locomotor suppression) of THC, WIN55,212-2, and XLR11 in wildtype, CB1-knockout, CB2-knockout, and GPR55-knockout mice. Pharmacological antagonists confirmed genetic findings.
What this study cannot tell us
Animal study using knockout mice, which may develop compensatory mechanisms. Only three cannabinoids tested from a large and diverse class. Tetrad effects are a simplified measure of cannabinoid pharmacology.
How to read the evidence
Well-designed preclinical study using both genetic and pharmacological approaches, but limited to mouse models and three compounds.
When this study was published
2020 animal study. Challenges the CB1-centric model of cannabinoid pharmacology.
The bigger picture
Understanding that plant and synthetic cannabinoids work through different receptor mechanisms could explain why synthetic cannabinoids produce more severe and unpredictable effects than plant cannabis, and could guide safer therapeutic development.
Questions still open
- Could GPR55 antagonists enhance the therapeutic effects of medical cannabis? Do the different receptor requirements explain the different toxicity profiles of plant vs. synthetic cannabinoids? Would these receptor distinctions hold in human pharmacology?
Common questions
What is the tetrad test?
What is GPR55?
Read the original research
Different receptor mechanisms underlying phytocannabinoid- versus synthetic cannabinoid-induced tetrad effects: Opposite roles of CB1 /CB2 versus GPR55 receptors.
British journal of pharmacology, 177(8), 1865-1880
Citation
Wang, Xiao-Fei; Galaj, Ewa; Bi, Guo-Hua; Zhang, Cindy; He, Yi; Zhan, Jia; Bauman, Michael H; Gardner, Eliot L; Xi, Zheng-Xiong. (2020). Different receptor mechanisms underlying phytocannabinoid- versus synthetic cannabinoid-induced tetrad effects: Opposite roles of CB1 /CB2 versus GPR55 receptors.. British journal of pharmacology, 177(8), 1865-1880. https://doi.org/10.1111/bph.14958
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