We also determined levels of the primary metabolite of 2-AG, AA, after acute and repeated restraint stress. Our data indicate that both acute and repeated restraint stress robustly decrease AA levels in the BLA. These data are not surprising because AA is a substrate for cyclooxygenase-2, which is regulated by glucocorticoids (Yamagata et al, 1993). Pharmacological inhibition of MGL has been shown to elevate 2-AG and decrease AA levels, leading some authors to suggest 2-AG degradation by MGL regulates AA levels in vivo (Long et al, 2009; Nomura et al, 2008). However, as 2-AG is only elevated during the 10th restraint exposure, our data suggest that 2-AG degradation under physiological conditions exerts minimal regulation over AA levels in vivo. Furthermore, these data suggest that measurement of free AA does not provide an accurate reflection of 2-AG catabolism under physiological conditions, likely because of the complex regulation of this lipid by multiple metabolic pathways. Although further studies are required to determine the mechanisms subserving the alterations in 2-AG metabolism induced by repeated restraint stress, these data provide the first report of physiological alterations in the 2-AG precursor/metabolite profile in vivo.
