Characterizing the Mechanism of Magnetoreception in C57BL/6 Mice

项目总结。通过对C57 BL/6小鼠的磁罗盘定向行为分析，研究了小鼠感知地磁场的分子和生物物理机制。两种潜在的神经机制已经被证明足够敏感，足以让陆生动物探测到地球强度（50微特斯拉）的磁场：涉及铁磁磁铁矿粒子的机制（“磁铁矿机制”）和涉及形成自由基对中间体的光诱导生化反应的机制（“自由基对机制”）。实验室小鼠C57BL/6菌株的基因敲除被用来研究隐色素是否是小鼠磁罗盘的重要组成部分，隐色素被认为在基于自由基对机制的磁罗盘中起核心作用。小鼠实验还被用于测试：(1)自由基对机制假说的关键预测，即低水平、宽带（1-10 MHz）射频场会破坏磁罗盘的定向；(2)磁铁矿机制的关键预测，即磁罗盘的定向会被事先暴露在短暂、高强度的磁脉冲中破坏。最后，小鼠实验被用来确定射频干扰对磁罗盘响应影响的阈值。这项工作的潜在影响包括：(1)表征模型哺乳动物系统中磁场敏感性的生物物理机制；(2)证明哺乳动物系统对一类新的物理刺激（即~1-10 MHz范围内的射频场）的敏感性；(3)表征磁罗经的分子组成；(4)发展生物物理和遗传技术来操纵获取磁信息，这些技术可用于研究磁刺激在其他行为和神经生理反应中的作用（例如，啮齿动物空间记忆的行为和神经方面）。这项工作的广泛影响包括让本科生、研究生和博士后在神经行为学/感觉生物学和认知心理学的界面上接受独特的跨学科训练。

Project Summary. A behavioral assay of magnetic 'compass' orientation in C57 BL/6 mice is being used to investigate the molecular and biophysical mechanisms responsible for sensing the geomagnetic field. Two potential neural mechanisms have been shown to be sensitive enough for terrestrial animals to detect earth-strength (50 micro Tesla) magnetic fields: mechanisms involving particles of a ferromagnetic magnetite ("magnetite mechanisms") and mechanisms involving photoinduced biochemical reactions that form radical pair intermediates ("radical pair mechanism"). Genetic knockouts of the C57BL/6 strain of laboratory mouse are being used to investigate whether cryptochromes, proposed to play a central role in a radical pair mechanism-based magnetic compass, are an essential component of the mouse's magnetic compass. The mouse assay is also being used to test: (1) a critical prediction of the radical pair mechanism hypothesis, which is that magnetic compass orientation should be disrupted by low-level, broad band (1-10 MHz) radio frequency fields, and (2) a critical prediction of the magnetite mechanism, which is that magnetic compass orientation should be disrupted by prior exposure to a brief, high intensity magnetic pulse. Finally, the mouse assay is being used to determine the threshold for effects of radio frequency interference on the magnetic compass response. The potential impact of this work includes: (1) characterizing the biophysical mechanism responsible for magnetic field sensitivity in a model mammalian system; (2) demonstrating sensitivity of a mammalian system to a new class of physical stimuli (i.e., radio frequency fields in the ~1-10 MHz range); (3) characterizing molecular components of the magnetic compass; and (4) developing biophysical and genetic techniques for manipulating access to magnetic information that can be used to investigate the role of magnetic stimuli in other behavioral and neurophysiological responses (e.g., behavioral and neural aspects of spatial memory in rodents). Broader impacts of this work include exposure of undergraduate students, graduate students and post-doctoral fellows to unique interdisciplinary training at the interface of neuroethology/sensory biology and cognitive psychology.