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

[unreadable] DESCRIPTION (provided by applicant): [unreadable] The overall aim of this work is to investigate the neurobiological basis of behavioral sensitization to amphetamine in the context of individual differences. We aim to understand the interplay between psychosocial stress and the development of behavioral sensitization to amphetamine in the context of individual differences. Behavioral sensitization is relevant to drug addiction as it is thought that the neurobiological changes that may underlie sensitization to psychostimulants may be the same, or at least overlap with, changes that may cause addiction to drugs of abuse. Furthermore, it is thought that stress and glucocorticoids in particular, may mediate some aspects of behavioral sensitization as well as drug taking behaviors. We will examine how gene and protein changes in the dopamine and stress circuitry may mediate the propensity of some individuals to become sensitized to psychostimulants. We will use this model of individual differences to help understand how and why some individuals are more prone to the effects of drugs of abuse. [unreadable] [unreadable] [unreadable] [unreadable] [unreadable]

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 Drug addiction is a chronic brain disease characterized by compulsive use of drugs despite negative consequences. Risk of relapse remains elevated even after long periods of abstinence due to drug-associated cues that provoke drug craving and seeking. Currently, there are no effective pharmacotherapeutic interventions for addiction to stimulants, such as cocaine, highlighting the urgent need for further understanding of the neurobiology of addiction. In an animal addiction model of persistent relapse vulnerability, extended- access cocaine self-administration leads to an abstinent-dependent intensification of cue-induced cocaine craving, a phenomenon that has also been observed in human addicts. While the reward circuitry of the brain is known to play an important role in the drug-dependent plasticity that underlies the addiction disease, the hippocampus (HPC), a crucial member of the circuitry, has not been examined in the progression and maintenance of intensified cue-induced cocaine seeking. Our objective is to investigate the role of activin signaling in the HPC in cue-induced cocaine seeking following both acute and prolonged abstinence. Activin signaling was recently implicated in neuronal and behavioral plasticity following exposure to drugs of abuse, indicating that this pathway is a substrate mediating the long-term addicted disease state. Cellular processes in the HPC following cocaine exposure and prolonged abstinence have not been well studied. Therefore, deeper exploration of cocaine-induced plasticity in the HPC that may underlie relapse behaviors is desperately needed. The overarching focus of this proposal is to detail the molecular mechanisms of cocaine-induced cellular and behavioral plasticity in the HPC following abstinence to cocaine self-administration. To this end, we have proposed two Specific Aims. Following cocaine self-administration and subsequent abstinence, there is an increase in hippocampal activin A following re-exposure to cues previously paired with availability of cocaine during prolonged, but not acute, abstinence. We propose that activin signaling in the HPC is essential for the expression of intensified cue-induced cocaine-seeking behavior (Aim I). Furthermore, we propose that intensification of cue-induced seeking is mediated through activation of the understudied, non-conical activin signaling cascade in the HPC (Aim II). This application presents an opportunity to determine, for the first time, a causal mechanism of activin signaling in the hippocampus in the underlying cellular and behavioral plasticity induced by abstinence following cocaine self-administration. The corresponding research plan will elucidate a novel mechanism by which chronic cocaine exposure induces long-term adaptations in the HPC and will provide new direction 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: Opiate 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. Thus, there is a crucial need for novel therapies to treat opiate dependence and cravings occurring with abstinence, which lead to relapse. Many studies indicate dysfunctional brain circuits in opiate use and abstinence, while other studies have identified distinct molecular adaptations underlying opiate-induced behaviors. Such studies emphasize a need to approach opiate use from a combined circuit and molecular perspective to link candidate opiate use and abstinence molecules to dysfunctional neuronal subtypes. This could uncover molecules in disease vulnerable neuron subtypes that can be pharmacologically targeted for opiate use therapeutics. The neuronal subtypes in the nucleus accumbens (NAc) deserve considerable attention in opiate abuse. The NAc is a critical brain hub for altered molecular processes that mediate behavioral responses to opiates and other drugs of abuse. Further, we previously demonstrated distinct roles of the two NAc projection medium spiny neuron (MSN) subtypes, those enriched in dopamine receptor 1 vs. 2 (D1-MSNs vs. D2-MSNs), in opiate induced behaviors. However, there is little information into the molecular adaptations, and corresponding neuronal adaptations occurring in specific NAc neuron subtypes in opiate use and abstinence. To provide insight into this we will perform translatome profiling, using RiboTag, in the two MSN subtypes after opiate use. Since cellular and behavioral plasticity associated with opiate exposure occurs along a continuum we will perform this translatome profiling in D1-MSNs vs. D2-MSNs following abstinence from heroin self-administration at early and prolonged time periods. The studies proposed in this grant application will, for the first time, identify the distinct translatome adaptations occurring temporally following discontinuance of heroin in a cell-type-specific manner. Such studies are essential for uncovering molecules underlying cellular and circuit dysfunction in opiate use and abstinence, thus providing multiple avenues of investigation into the subtype-specific neurobiological underpinnings of opiate abuse.

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.