David M. Dietz, Ph.D. - US grants

DESCRIPTION (provided by applicant): The proposed studies investigate the role of activin receptor signaling cascades in mediating the long-lasting changes in the brain's reward circuits, which contribute to the complex behavioral abnormalities that comprise an addicted state. To date there is no effective pharmacotherapy for addiction to stimulants, such as cocaine, highlighting the dire need for further understanding of how such drugs of abuse re-wire the brain. Neuronal plasticity is considered a neural substrate of the long-term addicted state, but there is a scarcity of mechanistic evidence that explores the molecular mechanism of cocaine-induced structural plasticity. Guided by exciting preliminary data demonstrating that in the Nucleus Accumbens (NAc) of animals of self-administering cocaine, activin receptor expression and signaling is increased, this application will test the following hypotheses: (Aim I) cocaine self-administration regulates the activin receptor-Smad pathway. Consequently, following cocaine self-administration the activin-smad pathway regulates both (a) actin dynamics and (b) Smad gene targets; (Aim II) Activin-Smad pathways are key molecular mechanisms underlying cocaine-induced dendritic spine plasticity of NAc neurons following cocaine self-administration; (Aim III) Activin receptor and Smad signaling pathways directly mediate cocaine seeking and craving as measured by reinstatement behaviors. This application presents an opportunity to determine, for the first time, the causal role for TGFBeta/activin-smad signaling cascades in facilitating drug seeking behaviors by examining cocaine-induced plasticity on cellular (i.e. structural) and behavioral levels (i.e. reinstatement). The findings from the work in this application will elucidate mechanisms by which chronic cocaine exposure induces long-term changes in plasticity of NAc neurons, and provides new directions for the development of novel therapies for cocaine addiction.

ABSTRACT Opiate use, dependence, and addiction have dramatically increased to epidemic proportions in recent years. This is a reflection of the increased misuse of prescription opioids and abuse of illegal opiate drugs, such as heroin. Unfortunately, there are still relatively few effective pharmacotherapeutic interventions available for the treatment of substance abuse and addiction, most of which rely on a replacement therapeutic model. Neuronal plasticity is considered to be a substrate that mediates the long-lasting changes in the brain's reward circuit and a key component of the long-term addiction disease state. These neural adaptations occur in brain regions such as the nucleus accumbens and lead to long-term drug craving and drug relapse. Currently, there is a scarcity of mechanistic evidence that explores the molecular mechanisms of heroin-induced structural plasticity. The overarching focus of this proposal is to determine the functional cellular neurobiological mechanisms of heroin-induced behavioral plasticity. The proposed studies investigate the role of actin dynamics mediated through the actin-binding protein drebrin in heroin-induced plasticity, ultimately resulting in long-term drug craving and relapse behaviors. To this end, we have proposed three Specific Aims that will test the following hypotheses: to determine if heroin self- administration results in a persistent and epigenetically-mediated decrease in the actin-stabilizing protein drebrin, which in turn regulates actin turnover (Aim I); to determine that drebrin is an essential molecular mechanism underlying heroin-induced relapse-like behaviors and structural plasticity following abstinence from heroin self-administration (Aim II); and to determine if drebrin mediates drug seeking and structural plasticity in D1- and in D2-expressing medium spiny neurons following heroin self-administration (Aim III). This application presents an opportunity to determine, for the first time, a causal mechanism?drebrin?in the underlying cellular (actin dynamics; D1/D2 MSN cellular specificity), structural (morphological), and behavioral (reinstatement) plasticity induced by heroin. The findings from the work in this application will elucidate mechanisms by which chronic heroin exposure induces long-term changes in the plasticity of nucleus accumbens neurons and provides new directions for the development of novel therapies for heroin addiction.

PROJECT SUMMARY/ABSTRACT Opioid use, dependence, and addiction have dramatically increased to epidemic proportions in recent years, leading to substantial financial and societal health burdens, as well as an increasing number of overdoses. To combat this epidemic, it is imperative that we understand the neurobiological underpinnings that lead to opioid use disorder. We must identify disrupted neuron subtypes in the brain in opioid use disorders and dysregulated molecules within these neurons that underlie cellular, circuit, and ultimately behavioral adaptations. Use of rat drug self-administration (SA) and relapse assays, which are considered the best available animal models of addiction, will allow a more complete understanding of the molecular mechanisms underlying the genomic, epigenetic, and transcriptional-induced cellular plasticity that drives the long-lasting drug seeking and propensity for heroin relapse. We will perform genome-wide transcriptome and open-chromatin profiling of ventral pallidum (VP) projection neuron subtypes in rat heroin SA, both acutely following drug cessation and after prolonged periods of drug abstinence. Here, we focus on the VP as a critical node in the brain?s reward circuit. Our studies will profile VP neurons that project to the nucleus accumbens, ventral tegmental area, medial dorsal thalamus, and lateral habenula. We will then integrate the transcriptomic and epigenomic data with complementary transcriptomic and epigenomic datasets, including multimodal data from the BRAIN Initiative describing cell type diversity in the VP and its output circuits. We will reconstruct cell type-specific gene co-expression and open chromatin networks and identify hub genes predicted to have central roles in immediate and prolonged abstinence from heroin, which could underlie subsequent relapse behavior. This collection of datasets and models will be made available through a biologist-friendly web portal based on our BRAIN Initiative-funded Neuroscience Multi-Omic Analytics platform. Using the data generated we will develop rat gene loci-specific CRISPR epigenomic targeting tools to determine the functional significance of key hub genes that are regulated in VP projection neuron subtypes. To achieve this goal, we will employ rat models of relapse in combination with advanced CRISPRa and CRISPRi AAV tools to enhance or reduce transcription of key hub genes during heroin SA or abstinence from heroin SA followed by cue-induced reinstatement. The studies proposed in this grant application will, for the first time, identify the distinct heroin-induced gene network adaptations occurring temporally in a cell-type-specific manner within a novel neurobiological circuit.