Pharmacological evaluation of cannabinoid receptor ligands in a mouse model of anxiety: Further evidence for an anxiolytic role for endogenous cannabinoid signaling

Extracts of Cannabis sativa have been used for their calming and sedative effects for centuries. Recent developments in drug discovery have suggested that modulation of neuronal endogenous cannabinoid signaling systems could represent a novel approach to the treatment of anxiety-related disorders while minimizing the adverse effects of direct acting cannabinoid receptor agonists. In this study, we evaluated the effects of direct cannabinoid receptor agonists and antagonists and endocannabinoid-modulating drugs on anxiety-like behavior in mice using the elevated-plus maze. We found that the direct CB₁ receptor agonists (1R,3R,4R)-3-[2-hydroxy-4-(1,1-dimethylheptyl) phenyl]-4-(3-hydroxypropyl)cyclohexan-1-ol (CP 55,940) (0.001- 0.3 mg/kg) and 2,3-dihydro-5-methyl-3[(4-morpholinyl) methyl]pyrrolo [1,2,3-de]-1,4- benzoxazinyl]-(1-naphthalenyl) methanone mesylate) (WIN 55212-2) (0.3-10 mg/kg) increased time spent on the open arms (T_o) at low doses only. At the highest doses tested, both compounds altered overall locomotor activity. In contrast, Δ⁹-tetrahydrocannabinol (0.25-10 mg/kg) produced a dose-dependent reduction in T_o. The endocannabinoid uptake/catabolism inhibitor 4-hydroxyphenylarachidonylamide (AM404) (0.3-10 mg/kg) produced an increase in T_o at low doses and had no effect at the highest dose tested. The fatty acid amide hydrolase inhibitor cyclohexyl carbamic acid 3′-carbamoyl-biphenyl-3-yl ester (URB597) (0.03-0.3 mg/kg) produced a monophasic, dose-dependent increase in T_o. The CB₁ receptor antagonists N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4- dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide HCl (SR141716) (1-10 mg/kg) and N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H- pyrazole-3-carboxamide (AM251) (1-10 mg/kg) produced dose-related decreases in T_o. These data indicate that activation of CB₁ cannabinoid receptors reduces anxiety-like behaviors in mice and further support an anxiolytic role for endogenous cannabinoid signaling. These results suggest that pharmacological modulation of this system could represent a new approach to the treatment of anxiety-related psychiatric disorders.