Abstract
The use of minor cannabinoids has been advanced, in part, by the idea of providing relief from pain and inflammation without the burden of unwanted psychogenic effects associated with Δ(9)THC. In this regard, investigators have focused on the effects of minor cannabinoid activation / desensitization of peripheral sensory neurons on nociceptive signaling and/or peripheral inflammation. With a focus on peripheral nociception, four common minor cannabinoids: cannabidiol (CBD), cannabigerol (CBG), cannabinol (CBN) and cannabichromene (CBC) were studied in primary cultures of mouse Dorsal Root Ganglion (DRG) neurons. We queried if calcium responses induced by the four cannabinoids differed in potency of activation, neuronal size preference, and dose-response relationships. Additionally, we determined the dependence of CBD and CBN on key channel-receptors that are known to mediate pain and/or antinociception. Individually, CBD, CBG and CBC directed greater response magnitudes when compared to CBN. All four minor cannabinoids activated overlapping but distinct size populations of sensory neurons. CBD and CBG activated the widest range of DRG neuron sizes (smaller-larger) overlapping with smaller capsaicin-sensitive neurons. In contrast, CBN and CBC activated predominantly larger sensory neurons. CBD diverged from other minor cannabinoids in directing a linear dose-response profile whereas CBG and CBC directed sigmoidal dose-response profiles and CBN activated DRG neurons with an inverted U-shaped dose-response relationship. CBD-induced activation of DRG neurons was dependent on co-expression of the nociceptive channel TRPV1 plus cannabinoid receptor 1 (CB(1)R), whereas CBN-induced activation was independent of TRPV1. Overall, we observed that minor cannabinoids CBD, CBG, CBN and CBC differed in their activation of DRG neurons and directed unique activation properties across a diverse population of sensory neurons. Such differences underly the hypothesis that a combination (entourage) of complimentary minor cannabinoids can direct synergistic antinociceptive activity.