PROJECT SUMMARY: BEHAVIORAL PROJECT ICAL’s core hypothesis is that non-physiological activation of the endocannabinoid (ECB) system by cannabis exposure during adolescence permanently alters ECB signaling, ultimately causing persistent alterations in cognition and motivated behavior. In this project, we propose a comprehensive behavioral evaluation of rodents exposed in adolescence to THC. Using a well-validated set of behavioral tasks and standardized protocols congruent with other Projects, we will characterize male and female, rat and mouse behavior across carefully selected measures of reward, memory, cognition and emotion to determine the scope of persistent THC behavioral effects, and how alterations in ECB signaling within hippocampal and mesocorticolimbic circuits underlie such effects. We have two Aims. Aim 1: To characterize behavioral phenotypes caused by adolescent THC exposure. We will phenotype the effects of prolonged THC administration in adolescent mice and rats of both sexes (PND 30-43), a proxy for daily cannabis use in human teenagers. The animals will be tested in adulthood (PND 70+) on standardized behavioral assays within the domains of reward, memory, cognition, and emotion. Additional groups will compare THC effects in adult animals to determine whether adolescent exposure effects are developmental in nature, and will examine behavioral effects that may emerge as animals age (PND 300+). Following behavioral testing, brains will be processed for behavior-related c-Fos immunoreactivity to determine changes in behavior-related neural activity. Aim 2: To identify mechanisms of induction and maintenance of adolescent THC effects on behavior. We hypothesize that THC, via stimulation of cannabinoid CB1 receptors (CB1R) in adolescence, changes ECB signaling and plasticity mechanisms within hippocampal and mesocorticolimbic circuits, resulting in the persistent behavioral effects identified in Aim 1. In Aim 2.1 we will determine the CB1R-dependence of persistent adolescent THC effects. In Aim 2.2 we will investigate the behavioral functions served by adolescent THC-induced ECB dysregulation, using microinjections of selective pharmacological agents or silencing/enhancing of gene expression via targeted viral vectors. In Aim 2.3 we will utilize chemogenetic manipulations to characterize and correct adolescent THC-induced circuit activity changes. These studies will provide the first comprehensive examination of the behavioral and circuit-level mechanisms of adolescent THC effects under a standardized, validated protocol in rodents. In addition, they will provide a mechanistic framework in which to interpret the results of NIH’s prospective ABCD consortium, and will help reveal the true neurodevelopmental effects of teen cannabis use.