Monoacylglycerol lipase inhibition attenuates acute and anticipatory nausea in rats

This study investigates the role of the endocannabinoid 2-arachidonyl glycerol (2-AG) in regulating acute and anticipatory nausea in rats using the conditioned gaping model. The animals were systemically pretreated with MJN110, a selective monoacylglycerol lipase (MAGL) inhibitor, to enhance endogenous levels of 2-AG. Acute nausea was assessed using the taste reactivity model in which a flavour, saccharin, was paired with the administration of the emetic agent, lithium chloride (LiCl). Anticipatory nausea was assessed using a model of contextually elicited conditioned gaping in which a context was paired with the emetic agent, LiCl. Results indicated that MJN110 at the 10.0 mg kg-1 and 20.0 mg kg-1 dosage significantly attenuated acute and anticipatory nausea, as displayed by the significant reduction in mean number of gapes. This suppression was mediated by CB1 receptor activation as displayed by reversal of such effects when MJN110 was coadministered with the CB1 receptor antagonist, SR 141716. The results suggest that enhancement of endogenous 2-AG levels by MAGL inhibition may have anti-emetic potential. Keywords: 2-arachidonyl glycerol; monoacylglycerol lipase; endocannabinoid; nausea; conditioned gaping; CB1 receptor