A comparison of the discriminative stimulus effects of Δ9-tetrahydrocannabinol and O-1812, a potent and metabolically stable anandamide analog, in rats

Efforts to determine whether Delta(9)-tetrahydrocannabmol (Delta(9)-THC) and anandamide elicit similar discriminative stimulus effects have yielded conflicting results. The difficulty in establishing a discriminative cue to anandamide may be due to its metabolic instability. Rats were trained to discriminate either Delta(9)-THC or O-1812, a metabolically stable anandamide analog, from vehicle to avoid this issue. O-1812 and Delta(9)-THC substituted for each other; however, both drugs were more potent in the O-1812-trained rats. Further, O-1812 only substituted for Delta(9)-THC at response rate decreasing doses. The CB, antagonist, SR141716A, blocked the discriminative stimulus effects of both drugs but augmented their rate effects. O-1839, a VR1 agonist, failed to substitute for either cannabinoid. These results suggest that the discriminative stimulus effects of Delta(9)-THC and O-1812 are similar, but subtle differences also exist.