Paul E. M. Phillips - US grants

DESCRIPTION (provided by applicant): Rapid dopaminergic neurotransmission in the nucleus accumbens is implicated in the generation of goal directed behaviors, and is central to drug reinforcement. The amplitude of phasic dopamine release on repeated activation of dopaminergic neurons in not static, but undergoes dynamic gain modulation. This may be fundamental to generation of appropriate responses to environmental stimuli. Thus, disruption of the fine balance of mechanisms that dynamically control dopamine release could have dire behavioral consequences, particularly in responding to external cues. This type of abnormal behavior is apparent in addicts who show highly elevated responses to drug-related cues. Furthermore, there are several lines of evidence that key mechanisms that control dopamine release are disrupted following cocaine abuse. Therefore, a better understanding of the dynamic control of dopamine release and its dysfunction following cocaine use should generate important information about the pathophysiology of cocaine addiction. Realtime electrochemistry, that samples extracellular dopamine with subsecond time resolution, provides a unique opportunity to study these processes efficiently. The dynamics of dopamine release can be exposed using patterned activation of dopaminergic neurons and then quantified with a mathematical model. The first objective is to determine the mechanisms underlying these dynamics that control dopamine release in the nucleus accumbens in normal animals. This will be achieved by a systematic characterization. First, the locus will be determined for the dynamics by comparing dopamine responses to electrical stimulation of dopaminergic cell bodies with that of their axons. In this way the mechanisms that reside in the terminal will be distinguished from those in the cell body. Next, comparing dopamine responses before and after systemic administration of the dopamine receptor antagonist, haloperidol will establish whether dopamine chemical neurotransmission is a requirement for dynamic control. If it is then more selective antagonists (SCH-23390 and raclopride) will be used to determine whether the transmission is via D1-like or D2-like receptors. The second objective is to re-examine these processes following exposure to cocaine. The impact of acute (single dose) and chronic (seven daily doses) cocaine-exposure will be assessed by comparing dopamine release dynamics in these groups to controls. This data should provide a unique insight into the control of dopamine in behaving animals, and the effect of cocaine exposure on this.

[unreadable] DESCRIPTION (provided by applicant): How we decide to do what we do is one of the most fundamental questions in understanding the neurobiological control of behavior. From moment to moment throughout our lives, we are constantly making cost/benefit analyses to generate action plans that optimize outcomes. In weighing up the costs of an outcome from an ethological standpoint, one must consider how much physical effort is required, how long a wait will there be before the outcome is presented, the certainty of the outcome and any possible aversive consequences. In addition, we have evolved to respect social and financial costs. Deficits in dealing with costs can be manifested as lethargy, impulsivity, risk taking or compulsion - traits that cross diagnostic categories of psychiatric disorders. Dopamine may play an important role in dealing with these costs. For example, antagonism of dopamine is sufficient to lower the physical effort rats will make, or the amount of time they will wait to obtain greater rewards. Subsecond activity in dopamine neurons encodes the outcome value within a range of available rewards, and these rapid signals can promote decisions to engage in behaviors to obtain rewards. We propose that this fast transmission provides a threshold signal for the costs an animal should endure to obtain a reward. Since they encode the expected reward amplitude, this would drive animals to tolerate a higher cost for better (expected) outcomes. In order to test this hypothesis, we will use a series of operant decision-making tasks that allow us to assess cost/benefit analysis and normalize across different costs, while measuring dopamine transmission with fast-scan cyclic voltammetry. In addition to investigating the subsecond temporal correlation between dopamine and behavior, we will also test causality of rapid dopamine release in cost/benefit decision making by electrically stimulating dopamine neurons. First, we will use a single-choice paradigm to test how dopamine in the nucleus accumbens encodes reward value and imposed effort or time costs. Next we will explore this signaling further when animals are choosing between two options that differ in reward magnitudes and in (time or effort) cost. Finally we will evoke dopamine release by electrically stimulating dopamine neurons at the exact time that an endogenous dopamine signal is generated - at the time of the initial stimulus at the start of the trial. This stimulation will boost the endogenous signal and thus test the effect of releasing more dopamine at the critical time during the behavior is sufficient to bias decision making towards higher-cost options. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): How we weigh up the costs and benefits of a potential outcome to guide choice is paramount to our everyday functioning. In making these economic decisions one must consider costs such as physical effort, the delay before the outcome is presented, the certainty of the outcome and possible aversive consequences, as well as social and financial costs. Dopamine plays an important role in dealing with these costs: antagonism of dopamine is sufficient to lower the physical effort rats will make, or the amount of time they will wait to obtain greater rewards. Dopamine is also implicated in risk-taking. Subsecond activity in dopamine neurons encodes the outcome value within a range of available rewards, and these rapid signals can promote decisions to engage in behaviors to obtain rewards. This fast transmission may provide a threshold signal for the costs an animal should endure to obtain a reward. Since they encode the expected reward amplitude, this should drive animals to tolerate a higher cost for better (expected) outcomes. However, during normal aging, there are several changes in dopaminergic systems, including a reduction in the expression of striatal dopamine receptors and in the biological capacity for striatal dopamine release. This raises a number of questions: 1) Is the diminished capacity for dopamine release reflected in the amount of dopamine released during economic decision making? 2) Do these age-related effects contribute to a change in economic decision making? To address these questions, adult (6-month-old) and aged (24-month-old) rats will be studied while they perform decision making to "purchase" food options by lever pressing. First potential behavioral differences in economic decision making between age groups will be probed. Quantitative differences in the cost the rats will forgo to obtain a larger reward offered concurrently with a smaller but cheaper reward will be tested. In one set of experiments, the currency of the imposed cost will be physical effort, where animals will be required to make a higher number of lever presses to receive the larger reward. In another set of experiments, risk-taking behavior will be tested by allowing rats to choose between smaller rewards and larger, but uncertain, rewards. Next, dopamine release will be measured in the ventral striatum (nucleus accumbens) of adult or aged rats during economic decision making. Dopamine will be monitored with subsecond resolution using fast-scan cyclic voltammetry. Using a single-choice paradigm, the way in which dopamine encodes reward value when reward is available for effort or probabilistic costs will be tested. Finally, the capacity of dopamine to modulate economic decision making in adult and aged rats will be tested by electrically stimulating dopamine neurons at the time within the task that an endogenous dopamine signal is normally generated. This evoked dopamine release will boost the endogenous signal and thus test the capacity of dopamine to overcome effortful or probabilistic costs. Collectively these experiments will provide unique insight into age-related changes in economic choice, dopamine transmission during decision making and their interaction. Cognitive, emotional and physical capabilities change during aging, in part by age-related changes in brain motivational systems. How these changes impact economic choices is unknown. The proposed work will use behavioral and neurochemical methods to study age-related changes in economic decision making in rats.

[unreadable] DESCRIPTION (provided by applicant): The development of drug addiction in humans involves a switch from experimentation and recreational drug use to compulsive drug taking and habit formation. Following this switch, the habit is rarely 'kicked', since periods of voluntary abstinence from drug taking are thwarted by intense drug craving that drives relapse. Even after extended periods of abstinence and conscious recognition of the long-term aversive consequences, the probability of relapse is high. This uncontrolled (compulsive) behavior is the hallmark of addiction. Release of dopamine into the extracellular space has been highly implicated in motivated behavior and is thought to have a central role in drug abuse. However, until recently it was not possible to measure it on a behaviorally-relevant timescale (seconds) in awake animals. With the development of fast-scan cyclic voltammetry, we have now successfully monitored and characterized dopamine release with subsecond resolution during cocaine self-administration in rats that had modest behavioral training, analogous to recreational drug use in humans. We now propose to extend this work to address one of the most pertinent questions in the study of addiction: what are the neurochemical correlates of the switch from recreational to compulsive drug use? The proposed work will study subsecond dopamine release in the nucleus accumbens and dorsolateral striatum in an animal model of addiction that incorporates habitual and compulsive drug taking. Insight into the neural substrates that promote these behaviors will be essential in fully understanding the neurobiology of addictions, and isolating therapeutic targets for the prevention and treatment of these devastating disorders. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): Classical conditioning is arguably the most fundamental tool we possess for adapting our behavior to a changing environment. Appetitive classical conditioning can be thought of as the process that establishes a learned association between reinforcement and the stimuli in the environment that signal its availability. This form of "reinforcement learning" provides organisms with a potent means to use predictive information to mold and guide preparatory action in an effort to maximize reward. The past three decades have been marked by major advances in our understanding of the neurobiological mechanisms that underlie reinforcement learning. In particular, short "phasic" bursts of neuronal activity in dopamine neurons, which are thought to produce rapid and transient increases in extracellular dopamine concentration throughout the striatum, have received considerable attention as a necessary component of the reinforcement process for both natural and drug reward. The central dogma in catecholamine research has held that dopamine transmission proceeds as a uniform broadcast signal from the midbrain to all target structures in the forebrain. However, there is mounting evidence that separate nuclei within the striatum may receive differential signals in response to primary rewards and conditioned cues at different stages in the learning process. It is hypothesized that this regional specificity in the dynamics and stability of dopamine signaling corresponds to the largely segregated roles in both learning and behavioral control that dopamine may play in these structures. The current proposal will test these hypotheses with three specific aims. Aim 1 will examine the impact of learning history and specific features of the task on the stability of phasic dopamine in the ventral striatum. Aim 2 will examine the influence of phasic dopamine on the activation of the striatum during different stages of learning and assess the coincident regional control of behavior. Aim 3 will examine phasic dopamine release in the ventral and dorsal striatum during multiple stages of reinforcement learning (acquisition, extended training and extinction) with the goal of correlating and comparing the development of specific behaviors to the profile of phasic signaling in each structure. PUBLIC HEALTH RELEVANCE: Although adaptive under normal circumstances, reinforcement learning is one of several contributing factors to the powerful control drug-related stimuli have over drug-seeking and drug-taking behaviors in many models of addiction. The phasic activation of the neuromodulator dopamine is implicated in both reinforcement learning and many aspects of drug abuse. The primary goal of this proposal is to examine the contribution of phasic dopamine release in specific brain regions to reinforcement and behavioral control.

DESCRIPTION (provided by applicant): Individuals in our society are required to make complex economic choices, often with uncertain outcomes, by integrating large amounts of information available to inform those choices. This daily requirement for decision making at all stages of life, together with increasing life spans and a growing accessibility to information among the youngest and eldest members of society, makes an evaluation of potential differences in decision making across age groups a critical area of research. Choosing advantageously among competing options with certain and uncertain outcomes is a product of individual subjective valuation of rewarding outcomes and the reinforcement learning processes required for accurately estimating those outcomes based on predictive information. Accordingly, a neuroeconomic framework of decision making under risk incorporating the contribution of age-related distinctions in subjective valuation and reinforcement learning provides a powerful tool for insight into the underlying substrates of choice behavior across the lifespan. The primary goal of the proposed work is to establish behavioral and neurobiological profiles of decision making under risk across the lifespan and examine the contribution of subjective reward valuation and reinforcement learning to these profiles at different life stages. We hypothesize that developmental/maturational changes in dopamine signaling from adolescence through adulthood and senescence is a fundamental contributor to choice behavior through the age-specific encoding of these essential components to the decision-making apparatus. We propose three specific aims examining dopamine signaling in the ventral striatum during probabilistic decision making, reinforcement learning, and subjective reward valuation in adolescent, adult, and aged rats.

DESCRIPTION (provided by applicant): Individuals in our society are required to make complex economic choices, often with uncertain outcomes, by integrating large amounts of information available to inform those choices. This daily requirement for decision making at all stages of life, together with increasing life spans and a growing accessibility to information among the youngest and eldest members of society, makes an evaluation of potential differences in decision making across age groups a critical area of research. Choosing advantageously among competing options with certain and uncertain outcomes is a product of individual subjective valuation of rewarding outcomes and the reinforcement learning processes required for accurately estimating those outcomes based on predictive information. Accordingly, a neuroeconomic framework of decision making under risk incorporating the contribution of age-related distinctions in subjective valuation and reinforcement learning provides a powerful tool for insight into the underlying substrates of choice behavior across the lifespan. The primary goal of the proposed work is to establish behavioral and neurobiological profiles of decision making under risk across the lifespan and examine the contribution of subjective reward valuation and reinforcement learning to these profiles at different life stages. We hypothesize that developmental/maturational changes in dopamine signaling from adolescence through adulthood and senescence is a fundamental contributor to choice behavior through the age-specific encoding of these essential components to the decision-making apparatus. We propose three specific aims examining dopamine signaling in the ventral striatum during probabilistic decision making, reinforcement learning, and subjective reward valuation in adolescent, adult, and aged rats.

Project Summary Stress exposure is one of the major triggers of unipolar depressive disorders, debilitating conditions whose core symptoms include changes in reward processing and responsiveness to environmental stimuli. However, despite the importance of this motivational dysregulation, the relationship between depression and neural processes that mediate appetitive responses to environmental has still not been precisely synthesized. We have identified a neurochemical signaling pathway that is disrupted by stress exposure in a manner that may be instrumental in mediating motivational symptoms of depressive disorders. We have demonstrated that corticotropin-releasing factor (CRF) increases dopamine release in the nucleus accumbens of stress- naïve male animals, but stress exposure ablates this neurochemical crosstalk for a prolonged period of time. In the proposed work we will directly characterize the role of CRF/dopamine interactions in mediating reward processing and its disruption by stress exposure and in particular the changes that take place in responding to reward-associated stimuli. We will also test whether CRF/dopamine interactions are similar in females or whether they are sexually dimorphic. The importance of integrating females into these studies is not only because they represent half of the population, but also because their response to stressors differ from those in males both quantitatively and qualitatively.

? DESCRIPTION (provided by applicant): Altered dopamine transmission is implicated in most contemporary theories of drug abuse, but the manner and even the direction of these changes are quite controversial. The most salient behavioral characteristics of the switch from recreational drug use to drug abuse are an increased focus on drug seeking and increased drug consumption. We recently demonstrated that increased drug consumption following chronic use is driven by a decrement in a specific dopamine signal: phasic dopamine release evoked by the response- contingent presentation of drug cues. However, our preliminary data indicate that phasic dopamine release to non-contingent presentation of drug cues (i.e., a potent stimulus for drug seeking and relapse to drug use during abstinence) change in the opposite direction and actually increase with chronic drug use. Collectively, this notion of diametric changes in phasic dopamine release to contingent and non-contingent drug cues, respectively, can resolve apparently contradictory theories of drug addiction. In the proposed work we will test this hypothesis by measuring dopamine release with fast-scan cyclic voltammetry and observing behavior to drug-related cues using different regimens of cocaine self-administration and following periods of drug withdrawal. We will also test whether or not the effect of L-DOPA on restoring dopamine release to contingent presentation of drug cues to reduce drug consumption is mitigated by increasing dopamine release to non-contingent cues and potentially increasing the likelihood of relapse. If not, and L-DOPA selectively increases depleted dopamine release (to contingent cues) without significantly elevating non- depleted dopamine (to contingent cues), we would advocate L-DOPA as a harm-reduction pharmacotherapeutic for reducing drug consumption to provide a window for behavioral and cognitive interventions.

? DESCRIPTION (provided by applicant): Adolescent alcohol use remains a major public health concern due in part to evidence implicating the age of initial alcohol use as a strong predictor fo the development of alcohol use disorders in adulthood. Recent reports evaluating the impact of drug abuse on society conclude that alcohol ranks as the most harmful of all abused substances. In addition, despite continuing efforts to curb its use, alcohol remains the most commonly used and abused substance among adolescents. That such experience can be antecedent to problem drinking has been recognized for some time; that such experience may also have long-lasting effects on decision- making processes is a relatively recent consideration. Moreover, it has been suggested that such deficits in decision making may represent a vulnerability to addiction. Indeed, people who engage in binge drinking at an early age show later deficits in decision making and increased likelihood of developing alcohol abuse problems. However, interpretation of these reports in humans has remained challenging due to the difficulty in separating the specific consequences of early drug use on future behavior from pre-existing factors that may contribute throughout the lifespan. We have demonstrated that rats exposed to alcohol during adolescence make maladaptive, risky choices as adults. This impairment represents a unique vulnerability of the developing brain as we have also shown that adult rats given identical exposure do not show this deficit. Adolescence has been characterized as a time of heightened risk-taking behavior in humans. Moreover, adolescence is a critical period of maturation when brain development, including that of the mesolimbic dopamine (DA) system, may be disrupted by alcohol. Mesolimbic DA is implicated in multiple aspects of reward processing and risk preference is sensitive to manipulations of striatal phasic DA signaling. Indeed, we have shown that striatal phasic DA release in response to risky options relative to safe options is significantly increased in alcohol-exposed rats. Further, there is a relative disinhibition in DA signaling during adolescence itself. Therefore, an appealing theoretical approach has been to link maturational changes in DA systems with behavioral changes in decision making and to posit that early life alcohol use confers a neurobiological profile that promotes persistent maladaptive decision making into adulthood. However, our findings to date are based on low levels of exposure that model recreational alcohol use while one of the defining features of use in human adolescents is a high incidence of binge drinking. Thus, in this proposal we aim to expand the scope and clinical relevance of our work by examining the consequences of binge alcohol use, which predominates in adolescence and is achieved by the NADIA AIE protocol. We hypothesize that increased risk bias, characteristic of the adolescent period, is attributable to mesolimbic DA systems and that exposure to AIE alters these circuits, resulting in a circuit-specific potentiation of midbrain DA neuron activity and persistent maladaptive decision making in adulthood.

Project Summary The University of Washington training program in the Molecular Pharmacology of Abused Drugs is designed to provide a cohesive training environment for five predoctoral and five postdoctoral fellows per year, interested in the molecular, cellular and behavioral pharmacological aspects of opioid, cannabinoid, and psychostimulant drug action, and their abuse. The program emphasizes training in research skills along with career development professional skills and responsible conduct of research-ethical skills. Faculty mentors provide training in a broad range of research approaches including molecular pharmacology, electrophysiology, neurochemistry, neuroinflammation, mouse genetics, viral-based gene expression, optogenetics, chemogenetics and behavioral pharmacology. In addition to the general, ongoing training typical at this vibrant institution, trainees in this program experience a coordinated series of events specifically designed for their benefit including invited speaker seminar sessions featuring internationally respected drug abuse researchers; monthly research progress meetings featuring local experts in abused drug research; weekly journal clubs on the current literature of opioid, cannabinoid and psychostimulant research; frequent opportunities for the trainees to enhance their presentation skills; courses organized for them on the 'Molecular Basis of Addiction' and 'Addiction: Mechanisms, Treatment, Prevention'; and career development seminars designed to strengthen their scientific and professional foundations. Faculty mentors are highly collaborative, and trainees benefit from a strongly interactive, multidisciplinary research program. The training program will continue to be a catalyst for research collaborations among the participating labs, for technology transfer between labs, and for newly funded collaborative NIDA- research grants. The trainees are drawn from an outstanding pool of candidates recruited to the participating graduate programs in Pharmacology and Neuroscience and to the well-respected laboratories as post-doctoral fellows. We have an active outreach program designed to encourage participation of underrepresented minorities and fellows from disadvantaged backgrounds. We actively train our students and fellows in responsible conduct of research and ethical treatment of animal subjects. The program is proud of its 25-year history of success in training fellows who have gone on to very successful scientific careers.

Abstract Cocaine abuse remains a major burden on public health with significant numbers of overdose deaths each year. The proposed work characterizes a neural circuit that underlies the increased drug consumption that takes place by some individuals following chronic drug use. This application leverages previous work demonstrating that corticotropin releasing factor (CRF), dynorphin and dopamine signaling can individually impact drug intake and that each of these systems changes with chronic cocaine use. Specifically, the proposed experiments ask how these three neuromodulatory systems interact with each other in the regulation drug consumption. The working hypothesis is that escalation of drug intake following chronic drug use, comes about through a serial pathway where elevated CRF levels causes an increase in dynorphin which consequently reduces dopamine release, producing escalation. However, the experiments are designed to systematically test the functional connections between each of these nodes in the regulation of cocaine intake and, in doing so, discern between eight competing models of the interactions. Therefore, regardless, of whether the results match the working hypothesis or not, the experiments will yield new insight into the interactions between these systems. This information will inform potential treatment targets for moderating intake in substance abusers and thereby reducing harm.