Both CB1 and CB2 receptors are G-protein coupled receptors. The CB1 receptor couples to both Gi/o proteins which function to inhibit adenylyl cyclase activity, activate potassium channels and inhibit voltage-gated calcium channels, while the CB2 receptor is only known to couple to Gi proteins (Howlett, 2002). The CB1 receptor appears to be located predominately on presynaptic axon terminals, and is capable of regulating calcium influx, and hence neurotransmitter release. Evidence shows that the endocannabinoid system has the ability to inhibit glutamate, GABA, acetylcholine, serotonin and norepinephrine release (Freund et al., 2003; Schlicker and Kathmann, 2001).
