Psychological trauma increases the risk of developing anxiety, depression and drug addiction. The endocannabinoid system, which comprises endogenous lipid-derived cannabinoid agonists and their G protein-coupled cannabinoid (CB) receptors, has been implicated in the modulation of stress responses, but its role in the response to traumatic events is unclear. In initial studies, I found that rats exposed to a life- threatening stimulus, the red fox pheromone TMT, display marked changes in the mobilization of the endocannabinoid, 2-arachidonoyl-sn-glycerol (2-AG) in select regions of the brain. These effects last for at least 7 days after the stress has occurred. I also found that pharmacological inhibition of monoacylglycerol lipase (MGL) - a lipid hydrolase that degrades 2-AG in presynaptic terminals - increases brain 2-AG levels and suppresses the anxiety-like behavior triggered by TMT. My findings suggest that (a) predator threat produces long-term changes in endocannabinoid 2-AG-mediated signaling in the brain;and (b) pharmacological interventions targeting MGL may provide a useful therapeutic strategy for the treatment of chronic brain disorders initiated by trauma. I will test these hypotheses with two specific aims.
Aim 1 : Effects of predator stress on brain 2-AG-mediated signaling. I will use a combination of molecular, biochemical and morphological approaches to investigate the impact of TMT on the expression of proteins involved in brain 2-AG-mediated signaling. I will target enzymes involved in 2-AG formation and degradation, as well as cannabinoid receptors. I will survey key regions of the brain implicated in stress control and investigate the time-course of the response over a period of 8 weeks. Based on my preliminary data, I expect that predator threat will cause long-lasting alterations in brain 2-AG signaling.
Aim 2 : Effects of MGL inhibition on chronic predator stress-induced anxiety. I will (a) characterize the dose-response of the anxiolytic-like effects of the potent and selective MGL inhibitor, JZL-184, verifying that such effects correlate with blockade of MGL activity;(b) determine, using pharmacological antagonists, if CB1 and CB2 cannabinoid receptors are involved in the response to JZL-184;(c) define the time window during which MGL is most effective in suppressing TMT- induced responses (e.g. immediately after trauma or later on, when trauma-related changes have been established);and, finally, (d) confirm the results obtained with JZL-184 using shRNA-mediated suppression of MGL expression. My hypothesis predicts that pharmacological and genetic interference with 2-AG availability will prevent the development of anxiety-like behavior elicited by predator threat. If successful, the proposed studies will demonstrate that acute life-threatening stress alters 2-AG signaling in specific regions of the brain, which in turn regulates the long-term response to the stressful event. My experiments will further suggest that pharmacological strategies aimed at enhancing 2-AG-mediated endocannabinoid signaling may offer a novel approach to the treatment of trauma-induced disorders such as anxiety, depression and drug addiction.
The brain naturally produces marijuana-like molecules called endocannabinoids, which are involved in the regulation of stress and anxiety. Building upon my preliminary findings that an acute traumatic event can result in long-lasting anxiety and significant changes in endocannabinoid regulation, the proposed research will test the hypothesis that pharmacological modulation of the endocannabinoid system might prevent the generation of anxiety states following a life-threatening trauma. This work is directly relevant to public health as it would advance our understanding of cellular processes underlying anxiety disorders and provide new insights on post-traumatic stress disorder, a highly prevalent and debilitating condition.
|Lim, James; Igarashi, Miki; Jung, Kwang-Mook et al. (2016) Endocannabinoid Modulation of Predator Stress-Induced Long-Term Anxiety in Rats. Neuropsychopharmacology 41:1329-39|