Mark J. Thomas - US grants

DESCRIPTION Addiction to drugs of abuse such as cocaine and ethanol is a major problem facing our society. Although basic research efforts have made great strides in understanding how drugs of abuse can usurp the function of the mesolimbic "reward pathway" of the brain, our knowledge of these mechanisms at the cellular level is far from complete. Research indicates that the serotonergic system plays a role in the mechanisms of drugs of abuse, especially cocaine and ethanol. At present, however, our knowledge of the effects of serotonin in key areas of the mesolimbic reward pathway, such as the nucleus accumbens (NAc), is lacking. The goal of the research outlined in this proposal is to elucidate the actions of serotonin (5-hydroxytryptamine; 5-HT) on excitatory and inhibitory synaptic transmission in the NAc using whole cell recording techniques in an in vitro brain slice preparation. These experiments will provide fundamental information about the role of serotonergic systems in the function of the NAc-information that is a prerequisite to understanding how the system may be altered by exposure to drugs of abuse.

DESCRIPTION (provided by applicant): Addiction is a chronic relapsing disorder. Despite extended abstinence, addicts may experience intense craving in response to drug re-exposure, cues or stress. How do strong cravings re-emerge and what are the neurobiological triggers? Nucleus accumbens (NAc) is a key target of addictive drugs in the mammalian brain. Animal models implicate NAc in enduring vulnerability to reinstatement of drug seeking. Although reinstatement involves plasticity in NAc AMPA-type glutamate receptors (AMPARs), the identity of this plasticity is unclear. Combining rodent reinstatement models with NAc whole-cell recordings in an ex vivo preparation, we identified a putative neural substrate for relapse. During cocaine abstinence, a cocaine prime, in vivo or in vitro, induces AMPAR long-term depression (re-exposure LTD), indicating that NAc AMPAR plasticity in response to environmental stimuli during abstinence is highly dynamic. We hypothesize that re- exposure LTD provides a synaptic gateway for reinstatement. To test this, we will directly measure and manipulate NAc AMPAR plasticity in drug-, cue- and stress-primed reinstatement and incubation models. In addition, priming in a dish gives us a tractable model system to study molecular mechanisms of reinstatement-linked plasticity. We hypothesize that propping up NAc AMPAR function during abstinence may be a useful tool in combating relapse.

b. Behavioral Phenotyping Core - Co-Directors: Laura Ranum and Mark Thomas Overview and Significance: Necessity of Core: Over the past few years, the need for a state-of-the-art mouse Behavioral Phenotyping Core has become apparent. Before initiating our current Core, investigators generating novel mouse models had to individually develop the tools to evaluate the phenotypes of their animals. Although there was enormous generosity among labs in providing tips, protocols and sharing equipment, consistent and informed advice on which tests to perform and the technical specifics of what really worked best were often not effectively communicated. This lack of centralization and standardization provided a barrier to some labs and a significant limitation in the number of tests that could be meaningfully performed by a single investigator. The expanded Core will foster interdisciplinary high impact work by providing centralized access to a standardized set of tests for motor and learning assessment and by implementing state-of-the-art mouse eyeblink conditioning tests in collaboration with Drs. Mark Stanton (University of Delaware), Dani Smith and Michela Gallagher (Johns Hopkins University). Purpose of Core: The goal of the Behavioral Phenotyping Core is to provide the highest quality assessment of the neurological status and specific behaviors in mice for Center investigators who use murine models to address basic biology or disease in the CNS. In mid-2008, we established a facility to consolidate, centralize and standardize mouse behavioral testing. This has improved productivity and data consistency and sparked several new collaborations between Center investigators. Due to a lack of full-time staffing, the current Core provides motor testing (open field, rotorod, gait analysis, raised beam, and grip strength), but only limited cognitive assessments (Morris water maze). We are strongly committed to increasing the capacity and extending the scope of the Behavioral Phenotyping Core to include additional tests for cognitive phenotypes. Based on our review of other current facilities (e.g. Baylor, University of Washington, UCLA, Johns Hopkins), and the impact our initial core activities have already had, we are confident that the Core will improve the quality and scope of behavioral testing and expand interdisciplinary collaboration¿a fundamental component of high-impact neuroscience research.

DESCRIPTION (provided by applicant): Dopamine (DA) is a critical neuromodulator in neural circuits for motor control, cognition and reward. A chief target of DA modulation is signaling of the excitatory neurotransmitter, glutamate. What are the basic principles for DA modulation of glutamatergic signaling and plasticity? Data addressing this question are maddeningly complex. Much of this complexity may be due to variations between cell types and circuits in which DA has been studied. What other factors might contribute to the heterogeneity? Using an ex vivo brain slice preparation of the nucleus accumbens (NAc)-a central component of the neural reward circuit-our pilot studies provide evidence for two additional factors: 1) in vivo exposure t novel stimuli and 2) the timing of DA signaling in relation to long-term potentiation (LTP) induction. We find that a brief exposure to novelty enables DA to induce a long-lasting depression in NAc AMPAR synaptic strength. We also find that prior DA signaling boosts the ability of tetanic stimulation to induce robust LTP. Using direct and sensitive electrophysiologica measures, we will investigate the roles for novelty and timing in DA modulation of NAc AMPARs. We expect our studies to inform new guiding principles for dopamine modulation in health and disease.

DESCRIPTION (provided by applicant): Addiction is a chronic relapsing disorder. Despite extended abstinence, addicts may experience intense craving in response to drug re-exposure, cues or stress. How do strong cravings re-emerge and what are the neurobiological triggers? Nucleus accumbens (NAc) is a key target of addictive drugs in the mammalian brain. Animal models implicate NAc in enduring vulnerability to reinstatement of drug seeking. Although reinstatement involves plasticity in NAc AMPA-type glutamate receptors (AMPARs), the identity of this plasticity is unclear. Combining rodent reinstatement models with NAc whole-cell recordings in an ex vivo preparation, we identified a putative neural substrate for relapse. During cocaine abstinence, a cocaine prime, in vivo or in vitro, induces AMPAR long-term depression (re-exposure LTD), indicating that NAc AMPAR plasticity in response to environmental stimuli during abstinence is highly dynamic. We hypothesize that re- exposure LTD provides a synaptic gateway for reinstatement. To test this, we will directly measure and manipulate NAc AMPAR plasticity in drug-, cue- and stress-primed reinstatement and incubation models. In addition, priming in a dish gives us a tractable model system to study molecular mechanisms of reinstatement-linked plasticity. We hypothesize that propping up NAc AMPAR function during abstinence may be a useful tool in combating relapse. The aim of this K02 proposal is to provide an opportunity for career development and training in state-of-the-art research methods to support our program studying the neurobiology of addiction relapse. Specifically, I plan to develop expertise in two areas: 1) the use of optogenetics as a means to probe pathway-specific plasticity in neural reward circuits and 2) gold standard preclinical addiction relapse models in mice. This expertise will directly enhance my current R01-funded research described above. Furthermore, this opportunity to stay abreast of new approaches for modeling human diseases in experimentally tractable species and for measuring and manipulating neural circuit plasticity is critical for long-term success in my research field.

? DESCRIPTION (provided by applicant): It is a longstanding goal in neuroscience to reveal how specific cell types contribute to different neural circuits that underlie cognition, behavior, and disease pathology. Although cell types can be grouped into descriptive categories (excitatory, inhibitory, peptidergic etc.), we know there is a great combinatorial diversity of cels that differ in ion channel and receptor expression levels and fulfill discrete roles within neural circuits. Thus, to improve the resolution of neural circuit maps, to understand how the brain works on a mechanistic level, and to better understand disease pathologies there is a great need for manipulating ever more specific sets of cell in neural circuits. Genetically targeting these different subsets is difficult when delivering transgenes to many neurons (with potentially adverse effects) and relying on cell-type specific promoters for selective expression - the current state of the art. Our agenda is to fundamentally change how cell type specific genetic manipulation is achieved: Since the functional definition of a neuron - its electrophysiological response to a stimulus - is intrinsically a proteomic problem, we propose a novel viral delivery method able to deliver transgenes selectively to neurons that express, on the cell surface, a targeted set of ion channels and receptors. When using this novel method transgene expression can be driven from generic and reliable promoters or other engineered promoter systems (e.g. sensitive to light or drugs). To achieve this transformative goal of a broadly useful tool for in vvo viral gene delivery, we build on Dr. Schmidt's expertise in protein engineering using genetically encoded peptide toxins, and Dr. Thomas' expertise with in vivo models of addiction disorders. In this application we describe the development of a generalizable method for creating engineered viruses with user-selectable tropism that can target specific subsets of neuronal cell types. We furthermore propose to demonstrate utility of these engineered viruses in intact brain tissue, including optogenetically targeting - without relying on transgenic animals or specific promoters - two sets of neurons involved in reward-related synaptic plasticity. The outcome of this work will be a broadly useful and first-in-class viral delivery technology that enables the genetic manipulation of defined sets neuron types in the brain based on what surface receptors they express. This method will enable completely new ways of exploring molecular and cellular mechanism of neural activity.

? DESCRIPTION (provided by applicant): Across all stages of drug use and abuse, women exhibit heightened responsiveness and hence greater vulnerability to the properties of addictive drugs. This is especially true regarding the increased susceptibility women exhibit towards drug relapse. In women, maximal vulnerability peaks during the follicular phase of the menstrual cycle when estrogen levels are at their highest. These findings have been recapitulated in female rodents, where estradiol heightens multiple measures of drug responsiveness and abuse. The mechanisms by which estradiol mediates enhanced vulnerability to drug relapse are completely unknown. The two PIs of this proposal have been independently studying the neurological underpinnings of relapse, and the mechanisms by which estrogens affect neuronal activity. Now working together, we have generated a unifying theory, whereby estradiol activation of estrogen receptor ? (ER?), localized to the surface membrane of medium spiny neurons of the nucleus accumbens shell (NAcSh), activates metabotropic glutamate receptor 1a (mGluR1a) signaling. Activation of ER?/mGluR1a signaling by estradiol is hypothesized to in turn promote mGluR5-induced relapse, a process mediated through the long-term depression of NAcSh afferents from the infralimbic cortex. To test this theory, the studies outlined in this proposal will utilize a recently developed mouse model of estradiol facilitation of drug relapse, taking advantage of electrophysiological, optogenetic and viral technologies. Collectively, these studies will provide a foundation to better understand and develop novel therapeutic approaches to treat drug relapse in women.

Project Summary Design of neuromodulatory devices targeting the kidney requires detailed knowledge of the structural and functional neurobiology of renal nerves. Our current understanding is fairly rudimentary and based on classical but outdated methodologies. For example, it is generally agreed that renal efferent nerves increase renin release, stimulate sodium reabsorption, and decrease GFR secondary to arteriolar constriction. However, the dose-response relationships for these effects are based on supramaximal electrical stimulation of renal nerves in anesthetized animals. Recent studies in conscious animals suggest this dogma may be incorrect. Even less is known regarding the structural and functional neurobiology of renal afferent nerves. Although it is well accepted that the renal pelvic wall in densely innervated, preliminary findings in our laboratory, as well as reports by others, suggest sensory nerves may also innervate vascular and tubular targets throughout the kidney. However, the physiological role of renal afferent nerves is unclear. Finally, it is well established that the afferent and efferent innervation of the kidney is heterogeneous. Distinct subsets of sympathetic renal nerves express the neuropeptides NPY and VIP. In the afferent renal innervation there is partial overlap of expression of the neuropeptides CGRP and SP and the capsaicin receptor TRPV1. In addition, our preliminary results demonstrate for the first time the presence of renal afferent nerves that express the sensory neuron-specific voltage-gated Na+ channel NaV1.8. The functional significance of the neurochemical diversity of renal afferent and efferent nerves represents a critical gap in our understanding of neural control of kidney function. Our central hypothesis is that efferent and afferent nerves with distinct neurochemical signatures differentially control renal functions through their association with distinct renal structures. We will use state-of- the-art neurophysiological and neuroanatomical approaches to generate an integrated functional and structural map of neural control in the mouse kidney. We will also initiate translation of these finding to the human kidney through comprehensive neuroanatomical analysis. In Specific Aim 1 will test the hypothesis that neurochemically distinct renal nerves differentially control renal function. In Specific Aim 2 we will test the hypothesis that neurochemically distinct renal nerves are associated with distinct structures in the kidney. Finally, in Specific Aim 3 we will define the structural neurobiology of renal efferent and afferent nerves, and their relationship to vascular, tubular and renal pelvis anatomy in the human kidney.

PROJECT SUMMARY: Pilot Projects Core The primary goal of the proposed NIDA Center for Neural Circuits in Addiction is to extend and enhance the research capabilities of NIH-funded addiction research projects at the University of Minnesota (UMN). The proposed Viral Innovation Core (VIC), Imaging Cells during Behavior Core (ICBC), Structural Circuits Core (SCC) and Addiction Connectome Core (ACC) will provide extensive technical expertise and infrastructure to individual investigators. To complement these efforts, the Pilot Project Core (PPC) will provide necessary means to foster new research and interactions by selecting and funding innovative projects that can synergistically combine the capabilities of the Research Cores to push the envelope in neural circuit research. The PPC, led by Center Director, Dr. Thomas, will engage a panel of Center faculty and External Advisors (i.e. the Pilot Panel) who will review proposals and present finalists to the Steering Committee for final determination. Following consultation with Program staff at NIDA, two to four projects will be funded each fiscal year. Proposals will be reviewed in accordance with standard NIH review criteria (significance, innovation, rigor and feasibility) and should address one or more of the following priorities: 1) ESIs; 2) New entrants to addiction research; 3) Demonstrate translational potential; 4) Engage a team of PIs who have not previously collaborated with one another; 5) Use Research Cores in a novel way; and/or 6) Develop substantial new capabilities for one or more Research Cores. Inclusion of preliminary data is not required. Applications for bridge funds or to extend ongoing projects will not be entertained. Finally, the Pilot Panel will also work on research dissemination so that Center members have the opportunity on a regular basis to see specific applications of Research Core functions, which we expect will stimulate creative new uses for these functions and new collaborations. The Core has two Specific Aims: Aim 1 will establish the Pilot Research Program with the first two recipient teams. These include a project from New Investigators, Drs. Patrick Rothwell and Esther Krook-Magnuson entitled: ?Parsing Interneuron Diversity in the Nucleus Accumbens to Understand the Actions of Fentanyl? and a project from Drs. Matthew Chafee, Benjamin Hayden, and Jan Zimmernann titled ?Front-Parietal Circuit Manipulation in Macaques.? Their team is composed of an ESI (Zimmermann) and two established investigators, forming a new collaborative team. Proposed awards are $50k over a period of up to two years. In Aim 2, the Pilot Panel, in consultation with the Steering Committee, will establish and maintain infrastructure, policies and procedures for award selection, ongoing evaluation and research dissemination of innovative pilot projects.

PROJECT SUMMARY/ABSTRACT This administrative supplement proposes to examine stakeholder views on deep brain stimulation (DBS) as a potential therapy for treatment-resistant addiction. This proposal extends the neuroscience work being conducted by the NIDA Center for Neural Circuits in Addiction (1P30DA048742-01A1) to address a critical near- term translational barrier: whether neurotechnology therapies like DBS, which are part of the Center's novel, circuit-oriented translational efforts, raise social and ethical concerns among key stakeholders. Work funded by this supplement will develop a critical ethics evidence base for the Center and the field of addiction research. This study will focus on two aims. The first is to conduct qualitative interviews with participants in addiction treatment and recovery about DBS. The study will capture participant's experiences with addiction and explore the ethical dimensions of DBS as a future treatment for addiction. The second aim is to collect both qualitative and quantitative data on perceived social support in addiction. The NIDA Center for Neural Circuits in Addiction aims to have a real-world impact on addiction and addiction treatment, including developing novel treatment interventions, like DBS. This project will both conduct bioethics research to help inform the development of deep brain stimulation in the area of addiction and will develop bioethics capacity through involvement of a bioethics trainee in qualitative interviewing.

PROJECT SUMMARY: Administrative Core The goals of the Administrative Core are to provide oversight and cohesive organization, so that the Aims across the Center can be achieved with both great efficiency and broad impact. The Administrative Core will be led by Center Director, Dr. Mark Thomas, Professor in the Department of Neuroscience. Dr. Thomas is a long-standing NIDA-funded investigator who has been researching the neural circuits underlying drug addiction since the late 1990?s. During his tenure at the University of Minnesota (UMN), he has launched two successful Core facilities and played a key role in the establishment of the UMN?s Medical Discovery Team on Addiction (MDTA). Our Administrative Core will be organized to fulfill the following Specific Aims: Aim 1 is to build and maintain an administrative framework with clearly defined roles and responsibilities. We designed our Center with several groups of investigators and advisors, each with well-defined roles and responsibilities, to carry out the mission of the Center. In addition to the Center Director and the Core co-Leads, these groups include the Steering Committee, responsible for governance of Center operations, and the Scientific Advisory Panel, composed of internal and external Scientific Advisors for each Core who are responsible for technology consultation and development. Working together, these entities will ensure the Center has the maximal impact on local and national science. Aim 2 is to develop and promote education, training and outreach opportunities for Core investigators. We propose a variety of measures that will promote: a) effective use of the scientific resources in the Center by individual investigators, regardless of their level of prior experience with the technologies; b) widespread dissemination of the science made possible by the Center; c) sharing of the technology and, when feasible, data sets, for use by the international scientific community; and d) outreach activities and events to inform the public of the Center?s scientific research.

This project seeks to develop electrical brain stimulation methods to reverse drug-induced pathological neuroplasticity. Addictions are difficult to treat in part because drugs of abuse transform reward and decision- making circuits, persistently remodeling them in ways that lead to persistent cravings. As a result, relapse rates are high even with gold-standard treatment. Animal studies using optogenetics and related technologies suggest that drug-induced plasticity can be reversed by targeted circuit manipulations. This is particularly true in circuits related to the nucleus accumbens (NAc), a ?hub? of brain reward circuitry. For instance, co-PI Thomas showed that chronic morphine exposure in mice strengthened an infralimbic cortex (IL) to NAc synapse. Weakening this same synapse blocked reinstatement of drug-seeking after a period of abstinence (a model of relapse). The challenge is that our circuit-directed tools for animals do not translate readily to humans. Electrical deep brain stimulation (DBS), particularly of the nucleus accumbens (NAc), is feasible in humans with addiction, but appears not to work reliably in its current form. This is in part because clinical NAc DBS uses approaches developed for Parkinson disease, without considering addiction biology. That is, it does not address the neuroplasticity problem. We propose to develop an electrical intervention that specifically targets pathological IL-NAc connectivity, based around the concept of timing-dependent plasticity. In short, if one structure (NAc) is stimulated only in response to changes in another?s (IL?s) activity, the synapses between then can be specifically strengthened or weakened, based entirely on the timing between the two events. Co-PI Widge has developed such activity-dependent stimulation methods for modulating fear-related amygdala circuitry. There is a long tradition of using similar approaches for rehabilitation of spinal cord injury and stroke. We will apply activity-dependent electrical stimulation to modify the IL-NAc circuit of Long-Evans rats, as a first step towards a human brain stimulation therapy. We will develop real-time IL-NAc connectivity measurement tools (Aim 1) and identify the electrical stimulation parameters (timing, intensity) that can de-facilitate the IL-NAc connection (Aim 2a). We will then apply those optimized methods to rats exposed to morphine in a conditioned place preference paradigm (Aim 2b), comparing our electrical approach to Dr. Thomas? existing optogenetic approach. We hypothesize that this activity-dependent electrical approach will be equally effective, while also being much easier to translate. Success would have near-term clinical potential. Dr. Widge is both a neural engineer and a brain stimulation psychiatrist, with specific experience in NAc DBS. Both PIs are affiliated with state-funded initiatives in addiction treatment development. We are well positioned to translate potential outcomes from this effort into novel, mechanism-informed treatments for addiction.

Project Summary With medical progress and growing efforts to empower individuals in making life-impacting choices, older individuals are thus more engaged in their behavioral and socioeconomic choices than ever before. These decisions are multifaceted and nuanced, but unfortunately, older adults often make poor socioeconomic decisions. Progress in medicine has not only led to increased life expectancy but it has also contributed to a rise in Alzheimer's disease (AD), the most common form of dementia, due to rapid increase in population aging and the current absence of AD-modifying therapies. Exploiting recent advances in judgement and decision-making neuroscience, we now propose a three-pronged effort designed to uncover whether and how A?-dependent mechanisms induce changes in circuits underlying various forms of decision-making and we have formed an investigative multi-PI team uniquely qualified to pursue these questions. Leveraging exciting new results from our joint group, we will test the central hypothesis that decision-making in AD mice is altered in a multifaceted economic- and sex-specific manner. In the light of novel findings reported in the preliminary results, we will i) test the hypothesis that aging impairs decision-making differentially in male and female mice, ii) test the prediction that decision-making is impaired in mouse models of AD and worsens with aging and iii) test the hypothesis that genetic, pharmaceutical and optogenetic intervention will improve decision-making in AD mouse models, thereby providing a preclinical proof-of-principle that decline in decision-making can be ameliorated.