Determining the role of tripartite cell populations in THC-Induced behavioral phenotypes

Project Summary Cannabis is the most popular drug used amongst adolescents with many teens using more frequently than ever. Although perceived as relatively harmless, adolescent consumption of ∆-9-tetrahydrocannabinol (THC), the main psychoactive constituent in cannabis, is associated with vulnerability to a variety of psychiatric conditions including addiction. Parallel to increased use in teens, THC content in cannabis is now at unprecedented levels, and emerging data shows use of high potency cannabis is specifically linked to the development of cannabis use disorder (CUD). Unfortunately, research determining how adolescent high-dose THC (HD-THC) exposure affects neurobiological circuits underlying psychiatric-like behaviors is still lacking. I therefore completed a battery of experiments to disentangle the long-term effects of high dose THC on reward responsivity and stress reactivity in rats. I observed that adolescent HD-THC (but not low dose) uniquely increased stress reactivity in adulthood, a phenotype implicated in addiction risk. In stressed HD-THC rats, RNAseq of the basolateral amygdala (BLA), a region implicated in stress reactivity and cognition, revealed distinct downregulation of astrocyte-specific genes concomitant to upregulation in excitatory- and inhibitory-related genes. HD-THC animals also exhibited decreased astrocyte process length and branching, indicating HD-THC-related stress reactivity is associated with perturbations in astrocytes both on a transcriptomic and morphological level. HD-THC rats also exhibited increased risky decision making and impulsivity after re-exposure to THC in adulthood, cognitive facets tightly linked to multiple psychopathologies including substance use disorders. THC-induced cognitive deficits correlated with BLA Gfap mRNA expression. These results indicate that astrocytes, and their interactions with neurons, likely play a significant role in THC-induced behaviors in adulthood relevant to psychiatric risk. The effect of adolescent HD-THC experience on the transcriptome and function of neuronal and astrocyte populations has yet to be explained. Under the guidance of my mentor, Dr. Yasmin Hurd, and mentorship committee, Drs. Anne Schaefer, Bin Zhang, Joseph Cheer, Eric Nestler, and Xiaosi Gu, I will use single-cell sequencing and fiber photometry to determine how adolescent HD-THC exposure affects astrocyte transcriptomic diversity and maturation (aim 1) and calcium activity (aim 2). I will then causally assess the role of astrocyte activity on THC- related phenotypes (aim 3). After modulating astrocytes using chemogenetics, I will examine the effect on neuronal transcriptomic landscape, as well as calcium activity during decision-making and after THC re-exposure in adulthood. This research program will provide novel mechanistic insights into the protracted effect of high-dose adolescent THC on astrocyte maturation, calcium activity and function in cognitive behavior while providing me key skills to help my transition toward becoming an independent investigator.