果蝇脑内温度感知VLP神经元感热信号通路及其功能研究

Environmental temperature has a profound impact on animal longevity, body weight, the ability to sense pain and circadian behaviors. Temperature sensors are evolutionally conserved. However, it is unclear how a range of temperature information is processed and integrated into neuronal circuits. The fruit flies provide an attractive system to study thermosensation because they offer a relatively simple biological system coupled with powerful genetic and physiological tools. So far, Anterior Cells (ACs) are only reported internal temperature sensitive neurons in the fly brain. In this project, we identified a small set of internal warmth-activated Ventrolateral Protocerebrum (VLP) neurons. Our current results showed that the VLP neurons and ACs have different temperature dependent responses. They do not have structural connections. Therefore, we hypothesize that they could contribute to distinct thermal sensing pathways, or VLP might be the downstream neurons of ACs. The structural connection between VLP neurons and circadian pacemaker neurons demonstrate that VLP neurons could be internal thermosensory neurons for environmental cycles of temperature, modulating circadian locomotion activity rhythms. In this project, neuronal circuits and functional effects of VLP neurons will be analyzed. Firstly, the physiological responses of VLP neurons to temperature increases will be determined. Then, we will test the possible up/downstream signaling cascade. At last, we will analyze how this temperature sensor contribute to Drosophila behaviors. The accomplishment of this project will reveal the neuronal mechanism of internal thermal sensory neurons in Drosophila and provide the groundwork of thermal sensation for the subsequent analysis of more complex systems.

环境温度对动物的寿命、体重、感知疼痛、昼夜节律行为等都有着深远的影响。动物温度感知系统高度保守，但其神经信号传导机制仍不清晰。果蝇因其相对简单的组织结构，极其丰富的遗传学和生理学工具，成为研究感温系统的优势模式生物。本项目将对果蝇脑内感热Ventrolateral Protocerebrum（VLP）神经元进行研究。预实验结果表明，其感热反应特点与目前唯一已知的脑内感热Anterior Cells（ACs）有显著不同，结构上不存在突触连接。VLP或是有别于ACs独立存在的另一类脑内感热神经元，或为ACs的下游。由于其与生物钟细胞可形成突触连接，我们推测其为生物钟温度循环感受器，调节生物钟节律。此项目将记录VLP神经元感热反应、研究其感温信号传导机制、分析其感热反应对果蝇的行为学意义。此项目的完成，将揭示果蝇脑内热感知神经元的作用机理，可为今后对更复杂温度感知系统的分析提供基础。

温度和光亮是对动物感受环境状态的重要因素。本项目对果蝇脑内感热Ventrolateral Protocerebrum（VLP）神经元进行了深入研究。我们发现VLP神经元在感受环境温度的同时，也可以受光激活。通过电生理，钙成像，免疫组化和药理学实验，我们确定VLP神经元可以接收小叶视觉投射神经元LT10和LT11，以及LC16神经元信息。解析了LC16神经元可以通过代谢型乙酰胆碱受体激活VLP神经元。对VLP神经元生理活性及其信号通路的研究，为了解光和热输入整合系统神经机制奠定了基础。与此同时，LC16-VLP神经元信号通路参与果蝇视觉运动检测，揭示了运动检测中存在的神经机制。再此基础上，我们进一步解析了果蝇运动检测视觉定向行为的神经机制。Lawf1神经元可以通过谷氨酸抑制L1和L2神经元的活性。这种抑制作用可能参与调节果蝇的视觉定向行为。为了全面探究果蝇视觉信号传导神经通路，我们分析了果蝇幼虫视觉信息输入系统。不同于果蝇成虫，果蝇幼虫表现出光回避行为。促前胸腺激素（Prothoracicotropic hormone，PTTH）神经元对果蝇幼虫感光系统及避光行为起着决定性的作用。通过在体电生理，我们确定了光刺激可以显著抑制PTTH神经元的活性。通过钙成像，我们发现PTTH神经元存在多种神经递质输入通路，解析了神经递质调控果蝇幼虫发育的机制具有重要意义。本项目的完成，对揭示果蝇感热和感光系统的神经机制提供了重要基础。