Vagal afferent neurons abundantly express excitatory transient receptor potential (TRP) channels which strongly influence afferent signaling. Cannabinoids have been identified as direct agonists of TRP channels, including TRPA1 and TRPV1, suggesting exogenous cannabinoids may influence vagal signaling via TRP channel activation. The diverse therapeutic effects of electrical vagus nerve stimulation also result from administration of the non-psychotropic cannabinoid cannabidiol (CBD); however, the direct effects of CBD on vagal afferent signaling remain unknown. We investigated actions of CBD on vagal afferent neurons using calcium imaging and electrophysiology. CBD produced strong excitatory effects in neurons expressing TRPA1. CBD responses were prevented by removal of bath calcium, ruthenium red, and the TRPA1 antagonist A967079; but not the TRPV1 antagonist SB366791; suggesting an essential role for TRPA1. These pharmacological experiments were confirmed using genetic knockouts where TRPA1 KO mice lacked CBD responses while TRPV1 KO mice exhibited CBD-induced activation. We also characterized CBD-provoked inward currents at resting potentials in vagal afferents expressing TRPA1 that were absent in TRPA1 KO mice, but persisted in TRPV1 KO mice. CBD also inhibited voltage-activated sodium conductances in A-fiber, but not C-fiber afferents. To simulate adaptation resulting from chronic cannabis use, we administered cannabis extract vapor daily for three weeks. Cannabis exposure reduced the magnitude of CBD responses likely due to a loss of TRPA1 signaling. Together these findings detail a novel excitatory action of CBD at vagal afferent neurons which requires TRPA1 and may contribute to the vagal mimetic effects of CBD and adaptation following chronic cannabis use.
Keywords: CBD, cannabis, nodose ganglia, transient receptor potential, vagus