CNR1 and red-green color blindness: Drysdale et al. reported that the antagonists of CB1 (i.e., AM281) and TRPV1 (i.e., CPZ) enhanced the CBD-induced [Ca2+]i increase in hippocampal neurons, which implied that the CBD action on [Ca2+]i was regulated negatively by CB1 and TRPV1 [28].