Excellence in Research: Modulation of Synaptic Neurotransmitter Levels by Auto-receptors

神经递质水平的精确调节对神经系统的正常运作至关重要。多巴胺是一种重要的脑神经递质，在跨物种的运动控制中起着关键作用，从微观无脊椎动物到大型哺乳动物，包括人类。多巴胺的水平通过调节多巴胺释放到连接神经元之间的空间以及从该空间清除多巴胺而受到严格而精确的调节。突触多巴胺调节的生理机制尚不清楚。为了阐明多巴胺调节的机制，本项目使用了简单而强大的秀丽隐杆线虫模型，该模型具有明确定义的302个神经元神经系统，以揭示多巴胺自受体，多巴胺释放神经元上的突触前受体在体内的功能。秀丽隐杆线虫模型只有8个多巴胺能神经元，可以在其他更复杂的生物体中无法实现的水平上解剖多巴胺能信号。考虑到哺乳动物和秀丽隐杆线虫多巴胺能系统在细胞和分子水平上的相似性，这项工作的结果将有助于理解哺乳动物神经系统中多巴胺调节剂之间的相互作用，从而更普遍地为运动控制提供信息。这项研究还为特拉华州立大学（DSU）的高中生、本科生和研究生提供了宝贵的科学技术教育培训。特拉华州立大学（DSU）是一所以本科生为主的大学，也是一所历史悠久的黑人学院和大学（HBCU）。除了为代表性不足的学生群体提供高级培训外，这一努力还有助于加强DSU的研究环境。突触囊泡融合和神经递质清除的机制是高度受控的过程，其精细调节对神经系统的功能至关重要。自受体被认为通过影响神经递质合成、囊泡释放和神经递质清除来调节神经元功能。虽然各种神经递质的自受体已经被发现了几十年，但它们的作用机制仍不清楚。本项目的总体目标是了解神经元的功能和行为是如何通过体内突触神经递质水平的实时精确调节的。多巴胺的重要性被这样一个事实所强调，即它在整个系统发育中对具有保守细胞作用的广泛行为产生重要影响。这项研究利用秀丽隐杆线虫的简单而明确的神经系统及其强大的遗传模型，结合其透明的身体，允许在活体动物中对单个多巴胺能突触钮扣进行成像。这里要测试的假设是：多巴胺自受体通过控制突触囊泡融合的负反馈回路调节神经元活动，并通过与其他多巴胺调节因子（如膜多巴胺转运蛋白）的串扰来微调其功能。实验将测试多巴胺自受体在体内的行为和生理功能，同时用荧光共振在活体动物中观察光漂白后的单个突触，这种方法目前在哺乳动物中是不可行的。这些研究将推动D2自受体对突触多巴胺的调节作用的建立，并测试其与其他多巴胺调节剂的功能相互作用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Precise modulation of neurotransmitter levels is essential for apt functioning of the nervous system. Dopamine is an important brain neurotransmitter that plays a critical role in movement control across species, ranging from microscopic invertebrates to larger mammals, including humans. The levels of dopamine are regulated tightly and precisely through modulation of dopamine release into the space between connected neurons as well as clearance of dopamine from that space. The physiological mechanisms underlying the modulation of synaptic dopamine remain unclear. Towards the goal of elucidating the mechanism of dopamine modulation, the simple yet powerful C. elegans model with a well-defined 302-neuron nervous system is used in this project to uncover the in vivo function of dopamine auto-receptors, presynaptic receptors on dopamine-releasing neurons. With only 8 dopaminergic neurons, the C. elegans model allows dissection of dopaminergic signaling at a level not feasible in other, more complex organisms. Given the similarities of the mammalian and C. elegans dopaminergic systems at the cellular and molecular levels, results from this work will inform understanding of the interactions between dopamine modulators in the mammalian nervous system and thereby inform movement control more generally. This research also provides valuable educational training in science and technology for high school, undergraduate, and graduate students at Delaware State University (DSU), a predominantly undergraduate institution that is a Historically-Black College and University (HBCU). In addition to providing advanced training to an under-represented population of students, this endeavor helps strengthening the research environment at DSU.Mechanisms of synaptic vesicular fusion and neurotransmitter clearance are highly controlled processes whose finely-tuned regulation is critical for functioning of the nervous system. Auto-receptors have been suggested to regulate neuronal function by affecting neurotransmitter synthesis, vesicular release and neurotransmitter clearance. While auto-receptors for various neurotransmitters have been known for decades, the mechanisms by which they act remain unclear. The overarching goal of this project is to understand how neuronal function and behavior are regulated through real-time precision in synaptic neurotransmitter levels in vivo. The significance of dopamine is underscored by the fact that it critically influences a wide range of behaviors with conserved cellular roles across phylogeny. This research exploits the simple yet well-defined nervous system of Caenorhabditis elegans with its powerful genetics of the model, combined with its transparent body that allows imaging of individual dopaminergic synaptic boutons in living animals. The hypothesis to be tested here is: dopamine auto-receptors modulate neuronal activity through a negative feedback loop controlling synaptic vesicle fusion, and they fine-tune their function via cross-talk with other dopamine regulators such as the membrane dopamine transporter . The experiments will test the behavioral and physiological function of dopamine auto-receptors in vivo while visualizing individual synapses in live animals with fluorescent resonance after photo-bleaching, an approach not currently feasible in mammals. These studies will advance the field in terms of establishing the modulatory effect of D2 auto-receptors on synaptic dopamine, and test its functional interactions with other dopamine modulators.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.