Multiphoton Imaging of Thoughts of Food During Natural and Induced Hunger States

描述（由申请人提供）：在自然和诱导饥饿状态下对食物思想的多光子成像。为了描绘大脑的功能，神经科学家经常关注大脑在参与任务条件下对感觉刺激和运动动作的反应。然而，对于在“静息状态”中发生的更常见和代谢成本更高的过程的神经基础，如心理意象、渴望和其他可以有力影响未来行为的过程，我们知之甚少。例如，饥饿感可以选择性地诱发与食物相关的线索（如糖果包装）的图像，导致强烈的渴望和消费不健康的食物。人类神经成像研究告诉我们，物体的图像会导致大脑外侧皮质区域的活动增加，而实际观看这些物体会激活这些区域。大鼠皮层的电生理学研究为心理意象的细胞相关性提供了证据。基于这些对人类和大鼠的研究，我们假设饥饿信号引发了更高发生率的“食物线索回放”，定义为一组特定的皮质神经元的内源性再激活，这些神经元先前被发现对食物相关的感觉线索有选择性地做出反应。食物线索回放可能对预期奖励线索的再现至关重要。然而，食物线索回放的神经基础仍然知之甚少，因为以前的电生理努力通常只记录了几十个未识别的神经元在几分钟到几小时的短时间尺度上的活动。我们将利用新的双光子钙成像技术在清醒、头部固定的小鼠中测量食物线索回放，从而克服这些限制。这些方法将能够记录跨越所有六层外侧皮层的1000多个已识别皮层细胞体的相同种群的多个小时和数天的记录，以及大量杏仁核轴突输入到皮层的记录，这可能会使皮层偏向于特定食物线索的回放。首先，我们将评估这种食物线索重放的遗传小鼠模型是否捕捉到了人类饥饿驱动的食物思想的关键特征，包括在饥饿状态下增加的发生率，以及随后对感官食物线索和进食倾向的感知检测的增强。然后，我们将通过结合皮质成像和光遗传学工具来监测和可逆操纵下丘脑AgRP神经元的神经活动，研究食物线索回放的动机驱动因素，已知下丘脑AgRP神经元驱动小鼠强烈的食物寻找。这些实验将开始揭示特定动机——饥饿——可以选择性地诱导神经对食物线索的重放的机制。这种新型小鼠模型的建立将有助于临床疗法的开发和测试，这种疗法可以选择性地减少对不健康食品和其他成瘾物质的不适当想法，从而减少长期对食物和药物成瘾的渴望。更广泛地说，这项工作将为神经科学暗物质的基础和临床研究建立一个强大的平台：内源性大脑皮层活动。

DESCRIPTION (provided by applicant): Multiphoton imaging of thoughts of food during natural and induced hunger states. To map the functions of the brain, neuroscientists often focus on brain responses to sensory stimuli and motor actions during engaging task conditions. However, remarkably little is known about the neural underpinnings of far more common and metabolically costly processes that occur during the 'resting state', such as mental imagery, cravings, and other processes that can powerfully influence future actions. For example, hunger can selectively induce imagery of food-associated cues (e.g. a candy bar wrapper), leading to powerful cravings and consumption of unhealthy foods. Human neuroimaging studies have taught us that imagery of objects results in increases in brain activity in the same lateral corticl areas that are activated by actual viewing of these objects. Electrophysiology studies in rat cortex have provided evidence for cellular correlates of mental imagery. Based on these studies in humans and rats, we hypothesize that hunger signals elicit a higher incidence of "food-cue replay", defined as the endogenous reactivation of a specific set of cortical neurons previously found to respond selectively to a food-associated sensory cue. Food-cue replay may be critical for anticipating the reappearance of rewarding cues. Nevertheless, the neural basis for food-cue replay remains poorly understood because previous electrophysiological efforts typically recorded from only tens of unidentified neurons across short timescales of minutes to hours. We will overcome these limitations by measuring food-cue replay using novel two-photon calcium imaging techniques in awake, head-fixed mice. These methods will enable recording across many hours and days from the same population of over 1000 identified cortical cell bodies across all six layers of lateral cortex, and from large numbers of amygdalar axonal inputs to cortex that may bias cortex towards food-cue-specific replay. First, we will assess whether this genetic mouse model of food-cue replay captures the key features of hunger-driven thoughts of food in humans, including increased incidence during states of hunger, and subsequent augmentation of perceptual detection of sensory food cues and propensity to eat. We will then investigate the motivational drivers of food-cue replay by combining cortical imaging with optogenetic tools for monitoring and reversible manipulation of neural activity in hypothalamic AgRP neurons known to drive intense food seeking in mice. These experiments will begin to reveal the mechanisms by which a specific motivation - hunger - can selectively induce neural replay of food cues. Establishment of this novel mouse model will enable development and testing of clinical therapies that selectively decrease inappropriate thoughts about unhealthy foods and other addictive substances, thereby reducing the incidence of cravings that perpetuate food and drug addiction. More generally, this work will establish a powerful platform for basic and clinical research into the dark matter of neuroscience: endogenous cortical brain activity.