The role of calcium-activated chloride channels in olfactory signal processing

离子通道介导神经元中许多不同的信号过程，使其成为神经元信息处理研究的焦点。在这里提出的项目中，应该解决为什么脊椎动物的嗅觉受体神经元在它们的化学感觉纤毛中表达钙激活的氯离子通道的问题。嗅觉刺激转化为电信号的过程发生在这些纤毛中，而氯离子通道似乎在这一过程中起着核心作用。根据嗅觉研究中流行的工作假设，氯离子通道是细胞放大机制的一部分，增加了气味敏感性。一般认为，微弱的嗅觉刺激只有在这种放大作用下才能引起电刺激。对老鼠进行的一项新观察表明，氯离子通道在基因上被切除了，这使人们对这一观点产生了怀疑，因为缺乏氯离子通道的老鼠是有气味的。这里提出的项目是基于我们最近的发现，嗅觉受体神经元中的氯离子通道具有一种以前未知的特性：它们会失活。在气味刺激时，它们只会短暂地张开，然后就会关闭——即使是在长时间的刺激下也是如此。这一发现表明，通道活动的时间过程对其生理作用至关重要。因此，本项目将主要关注具有和不具有氯离子通道的小鼠信号处理的动态方面。野生型小鼠和氯通道敲除小鼠之间的差异将通过在1-12 Hz频率范围内重复的脉冲刺激中表征嗅球中的网络活动来研究。5-12赫兹的频率对应于老鼠的嗅探行为，这是一种加速的呼吸模式，典型的探索行为和近距离观察气味物体。将选择光遗传学方法来实现精确和可重复的刺激。光脉冲用于重复刺激小鼠，这些小鼠在所有嗅觉受体神经元中表达通道视紫红质。在这些网络研究的同时，通道失活的机制将在分子细节上进行研究，以及嗅觉受体神经元水平上的失活调节。该项目的目标是揭示氯离子通道活性和网络活性之间的关系，从而了解氯离子通道在嗅觉信号处理中的作用。

Ion channels mediate many different signaling processes in neurons, placing them in the focus of research into neuronal information processing. In the project proposed here, the question shall be addressed why the olfactory receptor neurons of vertebrates express calcium-activated chloride channels in their chemosensory cilia. The transduction from olfactory stimulus into electrical signals takes place in these cilia, and the chloride channels appear to play a central role in this process. According to the prevailing working hypothesis in olfactory research, the chloride channels are part of a cellular amplification mechanism which increases odor sensitivity. It is assumed that weak olfactory stimuli can only elicit electrical excitation if boosted by this amplification. New observation with mice, where chloride channels were genetically ablated, cast doubt on this notion, as the mice that lack the chloride channels can smell. The project proposed here is based on our recent discovery that the chloride channels in olfactory receptor neurons have a formerly unknown property: they inactivate. During odor stimulation, they open only briefly, then they close - even upon prolonged stimulation. This finding suggests that the time course of channel activity is critical for its physiological effect. Consequently, this project will primarily focus on dynamic aspects of signal processing in mice with and without chloride channels. Differences between wild-type mice and chloride-channel knockout mice will be examined by characterizing network activity in the olfactory bulb during repetitive, pulsatile stimulation in the frequency range of 1-12 Hz. Frequencies of 5-12 Hz correspond to the sniffing behavior of mice, an accelerated breathing pattern typical for explorative behavior and close inspection of odorous objects. An optogenetic approach will be chosen to achieve precise and reproducible stimuli. Light pulses are used for repetitive stimulation in mice which express channelrhodopsin in all olfactory receptor neurons. In parallel to these network studies, the mechanism of channel inactivation will be examined in molecular detail, as well as the regulation of inactivation on the level of olfactory receptor neurons. The goal of this project is to reveal the relation between chloride-channel activity and network activity and, hence, to arrive at an understanding of the role that chloride channels play in olfactory signal processing.