Neurodevelopmental Effects of THC on The VTA Dopamine System and Behavior

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PROJECT SUMMARY Marijuana is the most common illicit drug used by pregnant women. Clinical studies on the long-term effects of marijuana smoking during pregnancy show its detrimental impact on the cognitive development of the offspring from early childhood until later in life. In fact, children and adolescents exposed to the psychoactive ingredient of marijuana, Δ9-tetrahydrocannabinol (THC), before birth display reduced attention, learning and problem solving, hyperactivity, increased impulsivity and engagement in risk-taking behaviors. Hence, early exposure to THC might induce enduring adaptations encompassing the brain reward dopamine (DA) system resulting in maladaptive behavior, ranging from affective dysregulation to addiction vulnerability. However, preclinical studies on the impact of marijuana use on the development of brain reward pathways are surprisingly lacking. Hence, there is an urgent need to identify molecular substrates and effective strategies for prevention and treatment of these detrimental effects that might confer individual vulnerability. Here, we propose three experiments to test our overarching hypothesis that prenatal THC exposure induces a strengthening at afferent excitatory synapses on ventral tegmental area (VTA) DA neurons, which together with abnormal endocannabinoid (ECB) system function, induces a persistent excitatory drive to DA neurons underlying an at- risk phenotype for alcohol seeking. First, we will determine if prenatal THC exposure leads to strengthening of excitatory transmission onto VTA DA cells and we will examine the pathological reorganization of the ECB system's molecular machinery with nanoscale precision (Aim 1). Next, we will test whether offspring of THC- exposed dams display increased sensitivity to natural rewards and vulnerability to alcohol dependence in adulthood by means of biochemical and behavioral readouts (Aim 2). Finally, we will explore a postnatal pharmacological intervention to reverse the deleterious effects of prenatal exposure to THC (Aim 3). To our knowledge, these research issues have never been specifically addressed in this multi-disciplinary manner. We will test our hypothesis by exposing rat dams to THC during pregnancy and by combining ex vivo electrophysiological recordings, pharmacological manipulations, neurochemical detection schemes along with sophisticated Stochastic Optical Reconstruction Microscopy (STORM) super-resolution imaging and behavioral paradigms in the offspring of THC-treated dams. We will take advantage of the coordinated expertise of multiple laboratories and we will ensure that studies will be carried out in parallel rather than serially in a single laboratory. This will lead to an advance of scientific knowledge through international collaborative research that will simultaneously impact public awareness and policy makers of three different countries.