Inhibition of endocannabinoid neuronal uptake and hydrolysis as strategies for developing anxiolytic drugs

Abstract

The endocannabinoid system comprises the CB1 and CB2 receptors (the targets of the Cannabis sativa compound delta-9-tetrahydrocannabinol), the endogenous ligands (endocannabinoids) arachidonoyl ethanolamide (anandamide) and 2-arachidonoyl glycerol, their synthesizing machinery and membrane transport system, and the hydrolyzing enzymes fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), respectively. The endocannabinoids may act on demand to confer protection against aversive stimuli, which suggests that increasing their brain levels may represent an approach for treatment of anxiety-related disorders. Thus, this article reviews the profile of endocannabinoid reuptake and hydrolysis inhibitors in experimental tests predictive of anxiolytic activity. The FAAH inhibitors and the blockers of anandamide transport, in contrast to direct CB1 receptor agonists, induce anxiolytic effects at doses that do not interfere with motor activity. MAGL inhibitors also reduce anxiety-like behavior, although they are more likely to impair motor activity. Regarding their mechanisms, increasing anandamide levels induce responses mediated by the CB1 receptor and occluded by the transient receptor potential vanilloid type-1 channels, whereas the effects of increasing 2-arachidonoyl glycerol depend on both CB1 and CB2 receptors. Their neuroanatomical targets include various structures related to anxiety and fear responses. Understanding the pharmacological properties of FAAH and MAGL inhibitors may contribute toward the development of new anxiolytic interventions based on the endocannabinoid system.