CNS Dopamine as Marker for Obesity Predisposition: Link to Food and Drug Reward

描述(申请人提供)：饮食肥胖是一种在全球范围内迅速增长的流行病，解决这一公共卫生问题的有效方法是必要的。目前尚不清楚喂养的享乐因素在肥胖流行中的作用，其研究可能揭示调节对自然和药物奖励的易感性或抵抗力的常见机制。这项建议侧重于了解饮食肥胖倾向与食物和d-苯丙胺奖励所涉及的中枢多巴胺系统之间的联系。我们假设(到目前为止已经证实)大鼠的近交系肥胖倾向(OP)表型的特征是中枢多巴胺张力低，对食物和d-苯丙胺等刺激的多巴胺反应减弱。多巴胺反应的降低可能会导致实验室食物或苯丙胺摄入量的增加来补偿。下调多巴胺基调的蛋白质是肥胖倾向的潜在新标记物。适当的干预可能通过微调中枢多巴胺排泄来改变OP表型对放纵刺激(如高能量饮食或精神刺激剂)的敏感性。这一建议的具体目的包括：1)体重差异出现之前和之后，以及在进餐或苯丙胺挑战前后，肥胖倾向如何与多巴胺释放动力学联系起来；2)中枢多巴胺胞吐调节蛋白是否是肥胖倾向的标志；3)改变OP表型的发育和分子干预。近交系OP和肥胖抵抗(OR)大鼠将一直使用，因为它们在相同饮食下出现体重差异，并允许与饮食历史相关的影响区分开来。OP大鼠通过有利于体重增加的多基因遗传与人类肥胖易感性密切相关。按照多水平的方法，我们建议描述体内多巴胺的释放和行为；急性切片和原代细胞培养中的实时多巴胺胞吐；以及多巴胺胞吐调节因子的mRNA和蛋白质水平。初步结果表明，成年近交系肥胖和近交系OP大鼠基础水平、进食挑战和苯丙胺挑战细胞外多巴胺水平较低。成年OP大鼠酪氨酸羟化酶基因表达水平较低，而培养的OP新生大鼠多巴胺细胞培养中囊泡单胺转运体(VMAT2)蛋白水平较低。已提出的改变OP表型和相关中枢多巴胺神经传递的干预措施包括在PO日将OP胎仔与OR母鼠一起放置，在OP大鼠伏隔核过度表达VMAT2，以及对OP和OR大鼠进行配对喂养。

DESCRIPTION (provided by applicant): Dietary obesity is a fast growing epidemic worldwide and effective approaches for addressing this public health problem are necessary. The involvement of hedonic aspects of feeding in the obesity epidemic is still unclear and its study may reveal common mechanisms that mediate susceptibility or resistance to natural and drug rewards. This proposal focuses on understanding the link between dietary obesity predisposition and central dopamine systems implicated in food and d-amphetamine rewards. We hypothesize (and so far have confirmed) that the inbred obesity-prone (OP) phenotype in the rat is characterized by low central dopamine tone and reduced dopamine response to stimuli like food and d-amphetamine. The reduced dopamine response may lead to compensation with increased laboratory chow or amphetamine intake. Proteins that downregulate the dopamine tone are potential novel markers of obesity predisposition. Appropriate interventions may alter the susceptibility of the OP phenotype to indulgent stimuli (like high-energy diets or psychostimulants) by fine-tuning central dopamine exocytosis. The specific aims of this proposal include considering: 1) how obesity predisposition is linked to dopamine release kinetics before and after body weight differences arise and before and after a meal or an amphetamine challenge 2) whether regulatory proteins of central dopamine exocytosis are markers for obesity predisposition 3) developmental and molecular interventions that alter the OP phenotype. Inbred OP and obesity-resistant (OR) rats will be used throughout as they develop a weight difference while on the same diet and allow for distinction from diet history-related effects. OP rats closely model human obesity predisposition through polygenic inheritance favoring weight gain. Following a multi-level approach, we propose to profile in vivo dopamine release and behavior; real-time dopamine exocytosis in the acute slice and primary cell culture; and mRNA and protein levels of regulators of dopamine exocytosis. Preliminary results show that adult outbred obese and inbred OP rats had lower basal, meal-challenged and amphetamine-challenged extracellular dopamine levels. Tyrosine hydroxylase mRNA levels were low in OP adults, while the vesicular monoamine transporter (VMAT2) protein levels were low in OP neonatal rat dopamine cell cultures. Proposed interventions to alter the OP phenotype and associated central dopamine neurotransmission include placement of OP litters with OR dames at day PO, VMAT2 over expression in the nucleus accumbens of OP rats, and pair feeding of OP and OR rats.