Diet, Insulin, Dopamine, and Reward.

描述（由申请人提供）：慢性食物限制（FR）增加了滥用药物的奖励和运动激活作用。相比之下，高脂肪，肥胖促进饮食（OB）降低精神兴奋剂的敏感性相比，自由采食（AL）的标准啮齿动物的食物。这些发现表明，内分泌肥胖激素（如胰岛素）在调节大脑奖励途径中发挥作用。事实上，有证据表明胰岛素的这种作用，但机制使用体外伏安法获得的新的初步数据表明，nM水平的胰岛素增加诱发细胞外多巴胺（DA）浓度（[DA]o）在尾状核/壳核（CPu）和核丘脑（NAc）。值得注意的是，这种反应在FR大鼠中增强，但在OB大鼠中减弱。这个多PI项目的目标是测试的假设，胰岛素依赖的DA神经传递的变化有助于显着的饮食对大脑奖励回路的影响。初步数据表明，胰岛素增强诱发的[DA]o是由胰岛素受体（InsRs）介导的，而不是在DA轴突上，而是在胆碱能中间神经元上，并且显示出位于DA轴突上的烟碱乙酰胆碱（ACh）受体（nAChRs）对DA释放调节的关键作用。以往关于胰岛素对进食行为和奖赏的影响的研究强调了胰岛素在内侧下丘脑中的促食欲作用，暗示了在饱腹感中的作用。然而，我们的数据提供了一个新的作用，急性胰岛素升高的奖励，通过增强DA释放的证据。与这一假设一致，其他试点数据表明，较低的诱发[DA]o在CPu从FR大鼠切片，这是恢复外源性胰岛素。有趣的是，诱发的[DA]o在OB CPu中也较低。目的1中的机制实验将使用脑切片中的伏安法评估胰岛素对DA释放的影响的信号通路和电路，并测试低胰岛素血症导致FR大鼠中低诱发[DA]o的假设，而降低的InsR敏感性可能是OB中低诱发[DA]o的基础。目的2将结合联合收割机定量DA释放和摄取动力学与评估生理相关（低nM）水平的胰岛素对多巴胺转运蛋白（DAT）的表达和活性的轴突终末区和DA细胞体中的腹侧被盖区（VTA）的突触（神经元）体的影响。为了将这些体外研究中胰岛素的作用转化为体内行为，目标3中的实验将确定纹状体内胰岛素和胰岛素受体（InsR）拮抗剂注射对奖励性脑刺激和食物-药物配对环境的行为反应的影响。胰岛素抵抗和肥胖的患病率增加，以及饮食失调和药物滥用的高共病率表明，了解饮食，胰岛素，DA和奖励之间的联系将对预防和治疗成瘾性疾病具有重要意义。我们的初步发现，胰岛素促进递质的释放，包括DA和ACh的释放，表明胰岛素在脑功能中的一个全新的作用。在这个多PI、多学科项目中，机械体外研究和体内行为测定的结合具有很高的潜力，有助于病理性进食和药物成瘾的分解，并推动交叉治疗的发展，但人们对此知之甚少。

DESCRIPTION (provided by applicant): Chronic food restriction (FR) increases the rewarding and locomotor-activating effects of drugs of abuse. By contrast, high fat, obesity-promoting diets (OB) decrease sensitivity to psychostimulants compared to ad libitum feeding (AL) of standard rodent chow. These findings suggest a role for endocrine adiposity hormones such as insulin in regulating brain reward pathways. Indeed, there is evidence for such a role of insulin, but mechanisms Novel preliminary data obtained using in vitro voltammetry show that nM levels of insulin increase evoked extracellular dopamine (DA) concentration ([DA]o) in caudate/putamen (CPu) and nucleus accumbens (NAc). Notably, this response is enhanced in FR rats, but blunted in OB rats. The goal of this multi-PI project is to test the hypothesis that insulin-dependent changes in DA neurotransmission contribute significantly to the influence of diet on brain reward circuitry. Pilot data suggest that insulin-enhanced evoked [DA]o is mediated by insulin receptors (InsRs), not on DA axons, but on cholinergic interneurons, and show a pivotal role for DA release regulation by nicotinic acetylcholine (ACh) receptors (nAChRs) located on DA axons. Previous studies of effects of insulin on feeding behavior and reward have emphasized the anorexigenic effect of insulin in the medial hypothalamus, implying a role in satiety. However, our data provide evidence for a novel role of acute insulin elevation in reward by enhancing DA release. Consistent with this hypothesis, other pilot data indicate lower evoked [DA]o in CPu in slices from FR rats, which is restored by exogenous insulin. Interestingly, evoked [DA]o is also lower in OB CPu. Mechanistic experiments in Aim 1 will evaluate signaling pathways and circuitry underlying the effects of insulin on DA release using voltammetry in brain slices and test the hypotheses that hypoinsulinemia contributes to low evoked [DA]o in FR rats, whereas decreased InsR sensitivity may underlie low evoked [DA]o in OB. Aim 2 will combine quantitation of DA release and uptake dynamics with assessment of the effect of physiologically relevant (low nM) levels of insulin on dopamine transporter (DAT) expression and activity in axon terminal regions and in DA cell bodies in the ventral tegmental area (VTA) in synapto(neuro)somes. To translate the effects of insulin from these in vitro studies to in vivo behavior, experiments in Aim 3 will determine the effect of intrastriatal insulin and insulin receptor (InsR) antagonist injections on behavioral responses to rewarding brain stimulation and food- and drug-paired environments. The increasing prevalence of insulin resistance and obesity and the high comorbidity of disordered eating and substance abuse indicate that understanding the connections among diet, insulin, DA and reward will have important implications for prevention and treatment of addictive disorders. Our preliminary finding that insulin promotes transmitter release, including that of DA and ACh, indicates a completely new role for insulin in brain function. The marriage of mechanistic in vitro studies and in vivo behavioral assays in this multi-PI, multi-disciplinary project has high potential to help decompartmentalize pathological eating and drug addiction and to drive the development of crossover therapies are poorly understood.