Mitchell Roitman - US grants

psychomotor function; motivation; dopamine; dorsal raphe nucleus; serotonin; kynurenate; ethology; glutamates; frontal lobe /cortex; eating; psychopharmacology; microdialysis; behavior test; cats;

[unreadable] DESCRIPTION (provided by applicant): [unreadable] The rapid, subsecond signaling of the neurotransmitter dopamine (DA) and neurons in the nucleus accumbens (Acb) have been strongly implicated in cocaine seeking behaviors and drug taking in general. This Career Development Award will characterize the innate responses of DA and Acb cell firing to natural stimuli and how the responses change as a function of learning, motivation and endogenous peptide action. The award will also serve to train the PI in state-of-the-art electrophysiological and electrochemical techniques while he establishes his own independent line of research. In Experiements 1-3, DA and Acb activity will be rapidly sampled in two groups of animals using: 1) in vivo fast-scan cyclic voltammetry at carbon-fiber micrelectrodes (to measure subsecond increases in extracellular Acb DA) and 2) using chronically implanted microwire electrode arrays (to measure the electrophysiological activity of Acb neurons). In Experiement 1, the rapid responses of this system to rewarding (sucrose) and aversive (quinine) taste stimuli will be assessed in naive, untrained rats. In Experiment 2, the role of this system in learning cue-tastant associations will be determined by assaying it before, during and after classical conditioning of environmental stimuli to rewarding (sucrose) or aversive (quinine) tastant delivery. In Experiment 3, the integration of motivated state by this neural system will be assessed by recording rapid responses to the taste of a hypertonic sodium solution in rats with (rewarding) or without (aversive) a sodium appetite. In Experiment 4, the impact of peptides that affect food intake (leptin, melancortins) on rapid DA signaling in the Acb will be determined in an in vitro brain slice preparation. Effects of these peptides on rapid DA release would strongly support investigation of the use of these peptides not just in the treatment of obesity but in the treatment of drug addiction as well. These studies will establish the range of natural stimuli that promote rapid DA-Acb signaling - setting the foundation for examining aberrant signaling underlying drug addiction. [unreadable] [unreadable] [unreadable] [unreadable]

Project Summary/Abstract Combined, the preventable diseases of obesity and drug addiction impact an enormous number of people and cost billions to treat. Physiological need (e.g. thirst, hunger), its hormonal signals and related central circuits, modulate seeking for and consumption of both nutritive and drug stimuli and thus may serve as risk factors for overeating and drug relapse. Ventral tegmental area (VTA) dopamine neurons and dopamine release in the nucleus accumbens play critical roles in reinforcement. This mesolimbic system also integrates physiological state with primary reward and environmental cues to tune approach and consumption. Indeed, the parent grant of this competitive renewal determined that deviations from homeostasis potentiate phasic mesolimbic signaling evoked by cues predictive of restorative stimuli. It also determined that gut hormones signaling deviations from homeostasis act centrally to modulate phasic mesolimbic signaling in the context of both food and drug reward. Peripheral signals act on central ?first order? hypothalamic sites (e.g. subfornical nucleus (SFO), arcuate nucleus (ARC)) that have a permeable blood-brain barrier. Modulation of discrete populations of the SFO or ARC is sufficient to induce negative affect and modulate consummatory behavior for restorative stimuli in a manner consistent with negative reinforcement. How first order hypothalamic neurons communicate with the mesolimbic system for reinforcement and to bias approach and consummatory behavior is unknown. We hypothesize that parallel circuits for thirst and hunger access the VTA via lateral hypothalamic area (LHA) orexin neurons. As LHA orexin neurons are recruited during morphine withdrawal and orexin receptor blockade reduces negative affect associated with morphine withdrawal, we also hypothesize that aberrant activity in first order thirst and hunger circuits during morphine withdrawal are excellent targets for the treatment of negative affect and to break the cycle of addiction. While hypothalamic signals clearly modulate aspects of psychostimulant seeking and taking, their role in modulating responses to other classes of drugs ? chiefly opioids ? has received little attention. In light of the obesity and opioid epidemics and their co- morbidity, these are critical gaps in knowledge which will be addressed here. We will measure VTA dopamine cell body activity or nucleus accumbens dopamine release using in vivo fiber photometry in behaving rats while selectively modulating first and second order hypothalamic neurons. The aims of the proposal are: 1) to determine the mechanism by which first order thirst neurons (SFO) modulate phasic mesolimbic signaling to cues that predict water and drive approach; 2) to determine the mechanism by which first order hunger/satiety neurons (ARC) modulate phasic mesolimbic signaling to cues that predict food and drive approach; and 3) to intervene at the level of first order thirst and hunger neurons to modulate the aberrant dopamine signaling that contributes to the negative affective state of morphine withdrawal. Results will identify novel therapeutic targets for treating disorders of motivation, including obesity and opioid dependence.

DESCRIPTION (provided by applicant): Obesity and drug addiction are diseases that affect a disturbingly large percentage of the population, cost billions of dollars to treat, and represent a increasing drain on our health care system. One factor that contributes to the onset of these diseases is reward seeking behavior. As individuals become obese, they seek and consume food well beyond caloric need. As individuals become addicted, they seek and consume non-nutritive drugs. The mesolimbic system, comprising the ventral tegmental area dopamine neurons and the nucleus accumbens, critically participates in normal reward seeking behavior as well as maladaptive behaviors including the overconsumption of food and drug taking. It has been known for decades that physiological state (hunger, satiety) can modulate reward seeking behavior. However, the mechanisms by which this occurs remain unknown. Here, this gap in knowledge will be addressed by monitoring mesolimbic signaling in real-time during reward seeking behavior towards nutritive (food) and non-nutritive (cocaine, intracranial self-stimulation rewards. The parent grant of this competitive renewal contributed to the establishment of phasic fluctuations in mesolimbic signaling as critical for goal-directed behavior. Indeed, phasic fluctuations in mesolimbic signaling, which occur within hundreds of milliseconds of reward seeking and reward consumption, appear to be especially important for reward-directed behaviors and reinforcement. These fluctuations will be recorded using fast-scan cyclic voltammetry to assay dopamine levels and electrophysiology to assay the firing rates of individual nucleus accumbens neurons. Both techniques allow phasic signals to be correlated with discrete behavioral events in awake, behaving rats. The aims of this proposal are: i) to determine how accumulation of nutrients alters reward-evoked phasic mesolimbic activity during operant responding for food, cocaine or intracranial self-stimulation, and whether metabolism of carbohydrates is necessary for nutrient feedback on phasic mesolimbic signaling and reward seeking; ii) to determine whether central and intra-ventral tegmental area glucagon-like peptide 1 (GLP-1), a centrally active satiety signal, provides negative feedback for phasic mesolimbic signaling and reward seeking; and iii) to determine whether central and intra-ventral tegmental area ghrelin, a centrally active hunger signal, provides positive feedback for phasic mesolimbic signaling and reward seeking. The significance of this work is in the discovery of novel mechanisms underlying normal and maladaptive reward seeking. This will provide therapeutic targets, in both the periphery and within mesolimbic circuitry, for treating disorders of motivatio, including obesity and drug addiction.

DESCRIPTION (provided by applicant): Aversive environmental events (e.g. loss of employment, fight with spouse, etc.) influence the daily lives of all people by altering their emotional states, decision making, and motivated behavior. For individuals with substance abuse disorders who are attempting to remain abstinent, these unfortunate events are clinically relevent, as they are frequently cited as a principle cause of relapse. In order to develop strategies to protect against this important determinant of relapse, it is essential to thoroughly characterize mechanisms by which aversive stimuli influence affective and motivational neural circuitry. To that end, several decades of research have identified the nucleus accumbens as a critical limbic motor interface, heavily regulated by dopamine, where affective and associative reward information directly influence behavioral output. Unfortunately, the manner by which aversive stimuli regulate dopamine signaling remains poorly understood, with several studies producing conflicting results. These discrepant results reflect both parametric experimental constraints and the inability of traditional measures to resolve the role of dopamine with sufficient spatial and temporal precision. This proposal details several experiments that will combine optogentic, electrophysiological, and electrochemical approaches in behaving animals that have a history of cocaine self-administration to clarify the causal relationship between negative affect-inducing aversive environmental events, decreased dopamine signaling, and drug seeking. Simultaneously, these experiments will directly test the sufficiency of decreased dopamine signaling in modulating nucleus accumbens' electrophysiological activity, hedonic responses, and drug seeking. The studies will determine if site-specific modulation of these discrete circuits reverses negative affective responses and prevents drug seeking. Specific Aim 1 will determine the causal role of aversive stimuli in promoting cocaine-seeking and simultanously characterize the precise role of dopamine signaling in each stage of the process: from the experience of the aversive stimulus to the transition to the cocaine-seeking state. Specific Aim 2 will determine if the decreased dopamine signaling observed following the presentation of cocaine-predictive stimuli is sufficient to cause drug seeking, and if this effect can be blocked by regulating dopamine. Specific Aim 3 will determine the discrete influence of dopamine on the encoding of reward and aversion-related behaviors by nucleus accumbens neurons. Together, the results of the proposed studies will provide unprecedented insight into the mechanism by which aversive stimuli alter the affective state of the animal, dopamine signaling, and drug seeking. The goal is to identify an aversion-sensitive motivational pathway that can be manipulated to protect abstinent substance abusers from a principle cause of relapse.

Project Summary/Abstract Combined, the preventable diseases of obesity and drug addiction affect an enormous number of people. In 2016, the World Health Organization estimated that over 1.9 billion people were overweight and at risk for obesity- associated diseases. It also estimated that 5.6% of the world population (between the ages of 15-64) used illicit drugs. Vulnerable individuals seek food and drug initially for positive reinforcement. However, with repeated cycles of use, abstinence and relapse, negative reinforcement mechanisms, where individuals consume (food, drug) to eliminate feelings of negative emotion, are thought to develop and dominate. The mesolimbic dopamine system has long been considered as a neural substrate for positive reinforcement but more recently it has been shown to play a role in negative reinforcement as well. Negative emotion generated by external stimuli (e.g. restraint stress, foot shock) modulates the mesolimbic dopamine system. Internal signals, and in particular, those arising from physiological need (e.g. hunger, thirst) also generate negative emotion, enhance drug reactivity and promote relapse to seeking in abstinent individuals. Thus physiological need is a risk factor for relapse via negative reinforcement. However, the mechanisms by which the signals and circuits activated by the negative reinforcing properties of physiological need modulates dopamine signaling remains unknown. Sodium depletion is a strong interoceptive signal that generates a sodium appetite ? a natural motivated behavior that can be recapitulated in the laboratory using rodent models. Sodium depletion is an ideal foundation on which to determine how physiological need interacts with dopamine signaling through negative reinforcement because: 1) it causes a sign change in the value of hypertonic sodium solutions from aversive to rewarding, an effect reflected by phasic dopamine activity; 2) it can be recapitulated via activation of a select population of brainstem neurons in the pre-locus coeruleus expressing prodynorphin (Pre-LCPDYN); and 3) Pre-LC depletion-responsive neurons project directly to dopamine neurons. Here, we will use transgenic mice (PDYN-cre) to express light- sensitive opsins in Pre-LCPDYN neurons and determine, using brain slices and electrophysiology: a) if Pre-LCPDYN neurons project directly to dopamine cell bodies and b) the consequences of activation of Pre-LCPDYN terminals for dopamine cell body excitability. In awake and behaving mice, we will measure dopamine release in multiple dopamine terminal regions to determine if the activity of Pre-LCPDYN neurons is sufficient and necessary to recruit dopamine signaling to cues predictive of a hypertonic sodium solution. Finally, we will determine whether dopamine spikes are correlated with mice working to eliminate the activity of Pre-LCPDYN neurons. Collectively, these exploratory/developmental studies will determine if the satisfaction of physiological need drives dopamine negative reinforcement signals ? which, in turn, promote approach and consumption. The results will directly address how physiological need (hunger, thirst, sodium appetite) confers risk for relapse through recruitment of dopamine signaling.