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确定环境刺激是否需要行为反应。例如，神经系统必须设置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。该阈值应设置为能够检测和避免潜在的危险情况，但又不能太低，以至于普通声音会引起反应。过度惊吓反应在许多神经精神障碍中观察到，包括精神分裂症、创伤后应激障碍、焦虑症和成瘾。此外，该阈值应该能够被调制，使得例如个体将变得习惯于持续的大声刺激。虽然脊椎动物中已知和保守的后脑和脊髓回路的主要组成部分，惊吓反应的基础，调节惊吓阈值和调制的分子遗传机制还没有得到很好的理解。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，声惊吓反应是由两个双侧巨大网状脊髓神经元之一的Mauthner细胞的放电发起的，Mauthner细胞接收来自同侧听觉神经的直接突触输入。在放电时，Mauthner细胞直接激活对侧运动神经元以触发特征性的“C”-弯曲，启动逃避行为。通过最近的突变突变体的遗传筛选与缺陷的惊吓调制，我们确定了一个突变体，是超敏感的声音惊吓刺激。没有表现出过度活跃或任何其他缺陷的惊吓运动学，纯合子胡迪尼幼虫执行惊吓逃脱反应，以低水平的听觉刺激，未能引起逃生野生型鱼。这表明houdini基因在设置声音惊吓阈值方面发挥了作用。 这项计划的目的是确定胡迪尼在调节行为中的作用程度，并确定它调节声音惊吓阈值的机制。在目标1中，我将分析胡迪尼幼虫是否也对其他感觉方式的刺激过敏，以及它们是否表现出惊吓调制的缺陷，如习惯化和前脉冲抑制。我还将测试霍迪尼成人的超敏反应和焦虑，侵略和成瘾的范例。在目标2中，我将鉴定houdini基因并描述其时空表达。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。houdini突变体提供了一个令人兴奋的机会来理解，至少部分地，神经系统如何“决定”是否启动一个行为。这些实验不仅为进一步表征惊吓通路开辟了途径，也为焦虑症等疾病的潜在治疗干预开辟了途径。

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.