Modulation of Nac-DA Signaling by Learning, Motivational State and Peptides

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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.