Diet, Insulin, Dopamine, and Reward.

描述（由申请人提供）：慢性食物限制（FR）增加药物滥用的奖励和运动激活效应。相比之下，高脂肪、促进肥胖的饮食（OB）与随意喂养（AL）的标准鼠粮相比，降低了对精神兴奋剂的敏感性。这些发现表明，内分泌肥胖激素（如胰岛素）在调节大脑奖励通路中发挥了作用。使用体外伏安法获得的新初步数据显示，纳米水平的胰岛素增加尾状核/壳核（CPu）和伏隔核（NAc）中诱发的细胞外多巴胺（DA）浓度（[DA]o）。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项目的目标是验证胰岛素依赖性DA神经传递变化对饮食对大脑奖励回路的影响的假设。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，并且在DA轴突上的尼古丁乙酰胆碱受体（nAChRs）调节DA释放方面发挥了关键作用。先前关于胰岛素对摄食行为和奖励影响的研究强调了胰岛素在下丘脑内侧的厌氧性作用，这意味着胰岛素在饱腹感中起作用。然而，我们的数据为急性胰岛素升高通过增强DA释放在奖励中的新作用提供了证据。与这一假设一致，其他试点数据表明FR大鼠切片中CPu诱发[DA]o较低，外源性胰岛素可使其恢复。有趣的是，诱发[DA]o在OB CPu中也较低。Aim 1的机制实验将利用脑切片伏安法评估胰岛素对DA释放影响的信号通路和电路，并验证低胰岛素血症导致FR大鼠低诱发[DA]o的假设。而InsR敏感性降低可能是OB低诱发[DA]o的基础。目的2将DA释放和摄取动力学的定量与生理相关（低nM）胰岛素水平对突触（神经）小体轴突末端区域和腹侧被盖区DA细胞体中多巴胺转运体（DAT）表达和活性的影响结合起来。为了将这些体外研究中胰岛素的作用转化为体内行为，Aim 3的实验将确定肠腔内胰岛素和胰岛素受体（InsR）拮抗剂注射对奖励脑刺激和食物和药物配对环境的行为反应的影响。胰岛素抵抗和肥胖的日益流行以及饮食失调和药物滥用的高合并症表明，了解饮食、胰岛素、DA和奖励之间的联系将对成瘾障碍的预防和治疗具有重要意义。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全新作用。在这个多pi、多学科的项目中，体外机制研究和体内行为分析的结合具有很大的潜力，可以帮助分离病理性饮食和药物成瘾，并推动交叉疗法的发展，但人们对这种结合知之甚少。

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. PUBLIC HEALTH RELEVANCE: Eating disorders and substance abuse are significant health risks. The pathology of both involves brain reward circuitry, but whether the same pathways are affected is unclear, in part because of segregation of research on diet vs. drugs. This multi-PI, multi-disciplinary project is built around our preliminary evidence that insulin, a recognized regulator of satiety and metabolism, is also a reward signal in the brain. This project has the potential to change the way that insulin is viewed, and thereby lead to novel crossover therapies to treat both obesity and addiction.