PROJECT SUMMARY/ABSTRACT This proposal is responsive to RFA-DA-24-028, “Advancing Psychedelics Research for Treating Addiction (R01 Clinical Trial Not Allowed).” Substance use disorders (SUDs) are a public health crisis in the United States with few therapeutic options. SUDs are influenced by environmental factors including chronic exposure to psychological stress, which shares common mechanisms of neural circuit dysfunction with SUDs. For example, chronic stress disrupts mechanisms within limbic circuits controlling reward behavior, such as the nucleus accumbens (NAc) of the ventral striatum. Therefore, studying NAc circuitry in chronic stress may uncover new targets for SUDs. Psychedelics, particularly psilocybin, have emerged as powerful therapeutics to combat mood disorders and SUDs by boosting signaling via the 5-HT2A serotonin receptor. Recent work in mice has elucidated key mechanisms by which psilocybin and other psychedelics act on neurons. However, psychedelics exert effects on many cell types outside of the nervous system that express the 5-HT2A receptor, including peripheral immune cells. Yet, a key challenge in deploying psychedelics to control immune responses induced by stress is many of the immune cell types, networks, and behavioral consequences of their activity remain unknown. In preliminary studies I identified populations of peripheral immune cells that are recruited to the meninges in response to chronic psychological stress and respond to the psychedelic psilocybin through 5-HT2AR signaling. Immune cell-derived cytokines elevated in response to chronic stress decreased the expression of Inhba in NAc astrocytes, which boosted Activin A signaling in NAc neurons. In vivo genetic perturbation of Inhba in NAc astrocytes showed Inhba limits stress-induced helplessness behavior by decreasing Activin A production while Acvr2a perturbation in NAc neurons ameliorated stress-induced helplessness behavior. Psilocybin treatment ameliorated stress-induced behavioral deficits as well as immune cell recruitment by decreasing immune cell chemokine receptor and inflammatory cytokine expression, which was independent of corticosterone levels. Hence, these data suggest that psilocybin decreases pathogenic neuroimmune signals induced by chronic stress implicated in SUDs. I hypothesize that stress-induced immune cell recruitment triggers loss of Inhba expression in astrocytes, which boosts NAc neuron Activin A signaling to increase helplessness behavior. I will test this idea by: Defining the effects of psilocybin on 5-HT2A+ meningeal immune cells during chronic stress using nucleic acid cytometry (Aim 1); Determining how psilocybin-sensitive immune cells regulate astrocytes through genome- wide CRISPR screens (Aim 2); and Evaluating psilocybin-dependent 5-HT2A+ immune cell effects on reward behavior using immune cell genetic perturbations via bone marrow chimeras (Aim 3). IN SUM, this R01 tests the therapeutic potential of a psilocybin-sensitive neuroimmune circuit in chronic stress relevant for SUDs.

PROJECT NARRATIVE Psychedelics are considered important therapeutic agents for the treatment of several neuropsychiatric disorders, including substance use disorders (SUDs) and major depression. Both SUDs and depression share common etiological elements that predispose individuals to develop these diseases, including exposure to chronic environmental stress. This project focuses on a molecular mechanism implicated in SUDs that is triggered by immune cells following chronic psychological stress, and is sensitive to psilocybin treatment, which implicates a neuroimmune interaction induced by chronic stress to the predisposition of SUDs.