Endocannabinoids and the Control Of Behavior and Cardiovascular Function

National Institute On Alcohol Abuse And Alcoholism

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Abstract

The vagal gut-brain axis has been recognized as a vital regulator of metabolic, motivational, and emotional states. These include anxiety, depression, reinforcement, food and alcohol craving, and involve the endocannabinoid system. Our previous observations indicated that the brain non-penetrant CB1 receptor (CB1R) antagonist, JD5037, suppresses alcohol preference in mice by blocking CB1R in ghrelin-producing cells and hampering the permissive role of ghrelin to drink alcohol (Cell Metab 2019; 29: 1320-1333). In the previous reporting period, we have identified subsets of sensory afferent neurons of the nodose ganglion that express CB1 receptors, the activation of which promotes alcohol drinking. These neuronal subsets selectively expressed advillin and Phox2B proteins. In the current reporting period we further narrowed the type of CB1 receptor-expressing afferent neurons relevant to alcohol drinking behavior. Namely, nodose ganglion projections of Phos2B positive, CB1R expressing neurons have been detected in both the muscular and mucosal layers of the GI tract. These projections represent two non-overlapping populations of vagal afferents whose genetic markers are the Glp-1 receptor (Glp1r) and GPR65, respectively. To determine the contribution of these two populations of sensory neurons in CB1R-mediated alcohol drinking, we sought to eliminate CB1R from the muscular and mucosal layers of the gut by crossing Cnr1(lox/lox) mice with Glp1r(iresCre) or GPR65(iresCre) mice, respectively. The resulting mutant mice, i.e. muscular-specific CB1Rko and mucosal-specific CB1Rko and their respective littermate controls were assessed by Cre/lox based genotyping and confirmed by RNAscope. When these mice were analyzed in the two-bottle/free choice drinking paradigm, the deletion of CB1R in vagal afferents expressing GPR65 was sufficient to abolish the inhibitory effect of JD5037, whereas the drug remained fully effective after knocking out CB1R in Glp1r-expressing vagal afferents innervating the muscular layer. Thus, CB1R on vagal afferent terminals in the mucosal layer (where ghrelin-producing cells are localized) but not those in the smooth muscle layer are involved in the control of alcohol drinking. These data have been written up in a manuscript, which will be submitted shortly for publication.