Endocannabinoid ligands (CBD, Δ9THC, and Terpenes) inhibit excitability of mouse dorsal root ganglion neurons and exhibit synergistic inhibitory effects
The need for improved treatments for chronic pain has driven increased interest in cannabis-based therapeutics. Peripheral dorsal root ganglion (DRG) neurons, including nociceptors, express cannabinoid receptors (CB1 and CB2), suggesting that modulation of DRG excitability may provide an effective strategy for peripheral analgesia. Here, we investigated the effects of cannabidiol (CBD), {Delta}9-tetrahydrocannabinol (THC), terpene mixtures as well as cannabis plant extracts on neuronal excitability in small-diameter mouse DRG neurons using whole-cell current-clamp electrophysiology and assessed potential synergistic interactions. Both CBD and THC produced a concentration- and time-dependent inhibition of rheobase-evoked action potential firing, which were reversible in the presence of bovine serum albumin (BSA), both with similar estimated IC50 values of 5 M (. Terpene mixtures, as well as individual terpenes (linalool, {beta}-pinene, and myrcene), similarly reduced neuronal firing. Co-application of CBD with THC or terpenes enhanced inhibition, consistent with synergistic interactions and the known "entourage effect." Application of WIN55,212-2 (WIN), a non-selective cannabinoid receptor agonist, in the presence of CBD also accelerated the time-dependent inhibition of neuronal firing. The inhibition of firing by the CB2-selective inverse agonist JTE-907 indicated the presence of CB2 receptors on DRG neurons. Plant extracts from the Cannabis sativa leaves also reversibly inhibited neuronal firing. CBD and a terpenes mixture produced modest effects on hERG channels, whereas plants extracts had negligible effects. Collectively, these findings demonstrate that phytocannabinoids and terpenes suppress peripheral sensory neuron excitability via receptor-dependent and indirect mechanisms, supporting their potential as non-opioid analgesics. Their synergistic interactions suggest that multi-component formulations may enhance analgesic effects.