Modulatory Effects of "Minor" Cannabinoids in an in vitro Model of Neuronal Hypersensitivity

Effective treatment for neuropathic pain remains an unmet clinical need. The therapeutic benefits of the Cannabis plant are well known, especially for pain relief. Here, we have assessed ten "minor" cannabinoids for their analgesic effects in an established model of neuronal hypersensitivity, a key mechanism which underlies neuropathic pain.

Adult rat DRG neurons were cultured in medium containing 100 ng/mL nerve growth factor (NGF) and 50 ng/mL glial cell-line derived neurotrophic factor (GDNF) for 48 hours to sensitize the neurons. Ca²⁺ imaging was used to measure the responses to pain stimulation using capsaicin, and to determine the modulatory effects of the cannabinoids, in individual neurons.

Control neurons (nociceptors) showed robust responses of Ca²⁺ influx to capsaicin application, while neurons treated with ten minor cannabinoids tetrahydrocannabiorcol (THCC), cannabitriol (CBT), cannabidivarin (CBDV), cannabinol (CBN), cannabichromene (CBC), cannabichromevarin (CBCV), cannabicitran (CBCT), cannabigerol monomethyl ether (CBGM), tetrahydrocannabutol (THCB) or tetrahydrocannabiphorol (THCP), at concentrations of 0.001-100 μM, showed differential dose-related effects on the responses to capsaicin. Ca²⁺ influx in response to capsaicin application was completely inhibited for each compound in 35-78% capsaicin-sensitive neurons, while other neurons showed reduced responses. The opioid receptor agonist morphine and α2δ1- Ca²⁺ channel inhibitor gabapentin were also tested for comparison and showed similar results. All the cannabinoids tested here inhibited calcium influx in response to capsaicin, and two, namely, CBN and THCC elicited calcium influx at higher doses. Inhibition of Ca²⁺ influx due to cannabichromene (CBC) was reversed by the potassium channel inhibitor Tertiapin Q.

All the cannabinoids tested here inhibited TRPV1 signalling. CBC targeted K⁺ channels to block TRPV1 mediated Ca²⁺ influx, demonstrating potential analgesic effects in vitro.