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效果。相比之下，与标准啮齿动物食物的随意喂养(AL)相比，高脂肪、促进肥胖的饮食(OB)降低了对精神刺激剂的敏感性。这些发现表明，胰岛素等内分泌脂肪激素在调节大脑奖励途径中发挥了作用。事实上，有证据表明胰岛素具有这种作用，但用体外伏安法获得的新的初步数据表明，胰岛素的NM水平增加了尾壳核(CPU)和伏核(NAC)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项目的目标是检验这样一个假设，即DA神经传递中胰岛素依赖的变化显著地影响了饮食对大脑奖励回路的影响。实验数据表明，胰岛素增强诱发的[DA]o是由位于DA轴突的烟碱型乙酰胆碱(ACh)受体(NAChRs)介导的，而不是由DA轴突上的胰岛素受体(InsRs)介导的，而是由胆碱能中间神经元介导的。以前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下丘脑内侧的厌食效应，这意味着它在饱腹感中起到了作用。然而，我们的数据为急性胰岛素升高通过促进DA释放在奖赏中的新作用提供了证据。与这一假设一致的是，其他试点数据表明，FR大鼠脑片中诱发的[DA]o较低，这是由外源性胰岛素恢复的。有趣的是，诱发的[DA]o在OB CPU中也较低。Aim 1中的机械实验将使用脑片伏安法评估胰岛素对DA释放影响的信号通路和电路，并测试低血糖导致FR大鼠低诱发[DA]o的假说，而InsR敏感性降低可能是OB低诱发[DA]o的基础。目的2将结合DA释放和摄取动力学的定量以及生理相关(低NM)水平的胰岛素对突触(神经)体轴突终区和腹侧被盖区(VTA)DA细胞体中多巴胺转运体(DAT)表达和活性的影响。为了将这些体外研究中的胰岛素效应转化为体内行为，目标3中的实验将确定纹状体内注射胰岛素和胰岛素受体(InsR)拮抗剂对奖励大脑刺激以及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患病率不断增加，进食障碍和药物滥用并存的高发病率表明，了解饮食、胰岛素、DA和奖励之间的关系将对成瘾障碍的预防和治疗具有重要意义。我们的初步研究发现，胰岛素促进递质的释放，包括DA和ACh的释放，这表明胰岛素在大脑功能中扮演着全新的角色。在这个多PI、多学科的项目中，机制体外研究和体内行为分析的结合具有很高的潜力，有助于区分病理性饮食和药物成瘾，并推动交叉疗法的发展，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.