Genetic Analysis of Acoustic Startle Behavior and Circuits

描述（由申请人提供）：生存取决于能够准确地判断环境刺激是否需要行为反应。例如，神经系统必须设定一个适当的行为阈值，听觉刺激必须超过这个阈值才能触发惊吓反应。这个阈值的设置应该能够检测并避免潜在的危险情况，但又不能太低，以至于普通的声音会引起反应。过度惊吓反应见于许多神经精神疾病，包括精神分裂症、创伤后应激障碍、焦虑症和成瘾症。此外，这个阈值应该能够被调节，例如，一个人将习惯于持续的大声刺激。虽然脊椎动物惊吓反应背后的后脑和脊髓回路的主要成分是已知和保守的，但调控惊吓阈值和调节的分子遗传机制尚未得到很好的理解。在这里，我建议使用强大的斑马鱼模型系统来研究惊吓调节的机制。在鱼类中，声音惊吓反应是由两个巨大的双侧网状脊髓神经元（毛特纳细胞）中的一个的放电引起的，毛特纳细胞接收来自同侧听神经的直接突触输入。一旦被激活，毛特纳细胞直接激活对侧运动神经元，触发典型的“C”弯曲，启动逃逸行为。通过最近对惊吓调节缺陷突变体的基因筛选，我们发现了一个对声惊吓刺激超敏感的突变体。纯合子的胡迪尼幼鱼没有表现出过度活跃或任何其他惊吓运动学缺陷，对低水平的听觉刺激表现出惊吓逃跑反应，而野生型鱼则没有这种反应。这表明胡迪尼基因在设置声惊吓阈值方面发挥了作用。本提案的目的是确定胡迪尼在调节行为中的作用程度，并确定它调节声惊吓阈值的机制。在目标1中，我将分析胡迪尼幼虫是否也对其他感官模式的刺激过度敏感，以及它们是否在惊吓调节（如习惯化和脉冲前抑制）方面表现出缺陷。我还将测试胡迪尼成人的超敏反应，焦虑，攻击和成瘾模式。在目标2中，我将识别胡迪尼基因并表征其时空表达。在目标3中，我将揭示胡迪尼影响毛特纳细胞惊吓回路兴奋性的分子机制。胡迪尼突变体提供了一个令人兴奋的机会，让我们至少部分了解神经系统是如何“决定”是否启动一种行为的。这些实验不仅将为进一步表征惊吓途径开辟道路，而且还将为焦虑症等疾病的潜在治疗干预开辟道路。

DESCRIPTION (provided by applicant): Survival depends on being able to accurately determine if an environmental stimulus requires a behavioral response. For example, the nervous system must set an appropriate behavioral threshold that an auditory stimulus must surpass in order to trigger a startle response. This threshold should be set such that potentially dangerous situations are detected and averted yet not so low that common sounds will elicit a response. Excessive startle responses are observed in many neuropsychiatric disorders including schizophrenia, post-traumatic stress disorder, anxiety disorders, and addiction. Furthermore, this threshold should be able to be modulated so that, for instance, an individual will become habituated to persistent loud stimuli. While the principle components of the hindbrain and spinal cord circuits that underlie the startle response are known and conserved among vertebrates, the molecular-genetic mechanisms that regulate startle threshold and modulation are not well understood. Here I propose to use the powerful zebrafish model system to investigate the mechanisms of startle regulation. In fish the acoustic startle response is initiated by the firing of one of two bilateral giant reticulospinal neurons, the Mauthner cells, which receive direct synaptic input from the ipsilateral auditory nerve. Upon firing, the Mauthner cell directly activates contralateral motor neurons to trigger a characteristic "C"-bend, initiating escape behavior. Through a recent genetic screen for mutants with defects in startle modulation we identified a mutant that is hypersensitive to acoustic startle stimuli. Without displaying hyperactivity or any other defects in startle kinematics, homozygous houdini larvae perform startle escape responses to low-level auditory stimuli that fail to elicit escapes in wild-type fish. This suggests that the houdini gene plays a role in setting the acoustic startle threshold. The aims in this proposal will determine the extent of houdini's role in regulating behavior and identify the mechanisms by which it modulates the acoustic startle threshold. In aim 1 I will analyze whether houdini larvae are also hypersensitive to stimuli in other sensory modalities and whether they show defects in startle modulation such as habituation and prepulse inhibition. I will also test houdini adults for hypersensitivity and in anxiety, aggression, and addiction paradigms. In aim 2 I will identify the houdini gene and characterize its spatiotemporal expression. And in aim 3 I will reveal molecular mechanisms by which houdini affects the excitability of the Mauthner cell startle circuit. The houdini mutant presents an exciting opportunity to understand, at least in part, how the nervous system "decides" whether to initiate a behavior. These experiments will open up avenues not only for further characterization of the startle pathway but also for potential therapeutic interventions in conditions such as anxiety disorders.