Infrared Photoactivation of Inner-Ear Hair Cells

描述(申请人提供)：我们最近发现，脉冲红外辐射(IR)作用于半规管壶腹嵴，可引起一阶传入神经元剧烈且高度可控的反应。许多传入细胞锁相于刺激，并为每个IR脉冲激发动作电位。这使得IR刺激可以用来控制第8神经传递到大脑的动作电位的时间和速率。即使在长期的刺激下，细胞的反应也是强劲的。我们的体外心肌细胞实验数据表明，IR通过单转运体和Na+/Ca~(2+)交换器激活线粒体Ca~(2+)流量。目前尚不清楚线粒体IR的兴奋性是否也是毛细胞感觉上皮对IR的敏感度的基础，或者是否有其他机制在起作用。IR的作用机制将通过对4个特定目标的考察来确定。我们将1)建立脉冲IR和热的剂量-反应函数，2)量化细胞对IR的电生理和[Ca+]反应，3)记录IR对毛细胞的传入神经末梢的突触后电位和电流，4)检测IR兴奋性的线粒体成分。这些结果有望确定毛细胞对红外线光敏的基本机制。了解这一机制将对脉冲IR在基础科学中的应用产生直接影响(例如，激发线粒体钙瞬变与膜去极化电流)。研究结果还可能对利用IR作用机制的新的IR治疗干预措施和假体设备的开发产生重大影响。 公共卫生相关性：我们的结果表明，脉冲红外辐射(IR)应用于内耳感觉毛细胞上皮细胞可以用来控制传入神经动作电位的时间和频率。如果IR的兴奋性主要起源于毛细胞线粒体钙电流，如我们的数据所示，刺激将具有作为基础科学工具的巨大影响的潜力，并将为新型疗法和神经接口的发展提供机会。

DESCRIPTION (provided by applicant): We have recently shown that pulsed infrared radiation (IR) applied to the semicircular canal crista ampullaris in vivo evokes dramatic and highly controllable responses of first order afferent neurons. Many afferents phase lock to the stimulus and fire an action potential for each IR pulse. This allows IR stimuli to be used to control the timing and rate of action potentials transmitted by the 8th nerve to the brain. The cellular response is robust, even under long-term stimulation. Our in vitro data using cardiomyocytes indicates that IR evokes mitochondrial Ca2+ flux via the uniporter and the Na+/Ca2+ exchanger. It is not know if mitochondrial IR excitability also underlies the exquisite sensitivity of hair-cell sensory epithelia to IR, or if some other mechanism is at play. The mechanism of IR action will be determined through examination of 4 specific aims. We will 1) establish dose-response functions for pulsed IR and heat across a broad parameter space, 2) quantify cellular electrophysiological and [Ca2+] responses to IR, 3) record postsynaptic potentials and currents in afferent nerve endings evoked by IR applied to hair cells, and 4) examine the mitochondrial component of IR excitability. Results are expected to determine the fundamental mechanism of IR photosensitivity in hair cells. Knowing the mechanism will have immediate impact on how pulsed IR is used for basic science (e.g. to evoke mitochondrial Ca2+ transients vs. membrane depolarizing currents). Results also have potential for significant impact on the development of new IR therapeutic interventions and prosthetic devices that take advantage of the mechanism of IR action. PUBLIC HEALTH RELEVANCE: Our results show that pulsed infrared radiation (IR) applied to inner-ear sensory hair-cell epithelia can be used to control the timing and rate of afferent nerve action potentials. If IR excitability has primary origins in hair-cell mitochondrial Ca2+ currents, as indicated by our data, the stimulus would have potential for high impact as a basic science tool, and would offer opportunities for development of new types of therapeutics and neural interfaces.