Neurobiological mechanisms underlying changes in PTSD-like symptoms after cannabis use - PROJECT SUMMARY/ABSTRACT: Post-traumatic stress disorder (PTSD) has a high rate of comorbidity with cannabis use disorder (CUD). Indeed, in veterans diagnosed with CUD, PTSD is the most highly co-occurring disease. Moreover, patients with comorbid PTSD and CUD have greater drug use severity and show poorer treatment outcomes than patients diagnosed with either PTSD or CUD alone. Conversely, PTSD is often listed as a medical condition potentially ameliorated by cannabis use. However, the clinical literature is mixed regarding the effect of cannabis use on PTSD symptoms, with some earlier studies indicating cannabis use may self- medicate PTSD and newer literature arguing that it exacerbates PTSD symptoms and reduces treatment efficacy. Thus, the prevalence of PTSD/CUD comorbidity and the increasing legal status of cannabis in United States make it imperative to understand the mechanisms whereby cannabis use is potentially promoting or ameliorating PTSD symptoms. Using acute restraint stress combined with a rat cannabis self-administration paradigm, I recently found that cannabis use promotes two primary PTSD-like symptoms, avoidance coping behaviors (immobility in the defensive burying task) and the generalization of stress coping responses to a neutral stimulus not previously associated with stress exposure. These clinically relevant discoveries are the foundation for my K99/R00 Pathway to Independence proposal. This proposal aims to identify neurobiological mechanisms underpinning how cannabis use changes and potentially exacerbates PTSD-like symptoms. During the K99 portion, I will characterize, in a cell-specific manner, the neuroadaptations induced by the interaction between stress and cannabis use in the nucleus accumbens core (NAcore). To this end, I will combine in vivo zymography with confocal microscopy and digital rendering approaches to quantify changes in the tetrapartite synaptic plasticity, which includes changes in: morphology of D1- and D2-medium spiny neurons (MSNs), astroglia, and the extracellular matrix (ECM) (Aim 1). I will then use the in vivo single-cell Ca2+ recording from D1- and D2-MSNs in NAcore, to determine which cell type and what patterns of activity are associated with the exacerbating effects of cannabis use on stress responses (Aim 2). In the R00 portion, I will apply my K99 training to study how stress and cannabis affect the tetrapartite synaptic plasticity in ventral pallidum (VP), a primary accumbens output nucleus that translates rewarding and aversive stimuli into behavioral responses. I will assess the signaling between ECM, astrocyte and GABAergic neurons (VPGABA), as well as the expression of perineuronal nets (PNNs) following acute stress and cannabis use (Aim 3a). I will then evaluate the specific role of PNNs in the altering effects of cannabis use on stress responses (Aim 3b). Finally, I will use changes in intracellular Ca2+ to determine if exposure to stress-conditioned stimuli or neutral stimuli changes the activity of VPGABA after cannabis use (Aim 4). By examining tetrapartite plasticity in a brain circuit known to strongly regulate both reward and avoidance behaviors, I expect to identify new targets for regulating PTSD and CUD comorbidity.
