Genetic Analysis of Acoustic Startle Behavior and Circuits

描述(由申请人提供)：生存取决于是否能够准确地确定环境刺激是否需要行为反应。例如，神经系统必须设置适当的行为阈值，听觉刺激必须超过该阈值才能触发惊吓反应。这一阈值应该设置为能够检测到并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响应。在包括精神分裂症、创伤后应激障碍、焦虑症和成瘾在内的许多神经精神障碍中都可以观察到过度的惊吓反应。此外，这个阈值应该能够调整，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的，并且在脊椎动物中是保守的，但调节惊吓阈值和调制的分子遗传机制还没有被很好地理解。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，声学惊吓反应是由两个巨大的网状脊髓神经元中的一个，即从同侧听神经接受直接突触输入的莫特纳细胞的放电启动的。在放电时，莫特纳细胞直接激活对侧运动神经元，触发典型的“C”弯，启动逃逸行为。通过最近对惊吓调制缺陷突变体的遗传筛选，我们鉴定了一个对声学惊吓刺激高度敏感的突变体。在没有表现出多动或任何其他惊吓运动学缺陷的情况下，纯合的胡迪尼幼虫对低水平的听觉刺激表现出惊吓逃逸反应，而这些刺激无法在野生鱼类中引发逃逸。这表明，胡迪尼基因在设定声音惊吓阈值方面发挥了作用。这项提案的目的将确定胡迪尼在调节行为方面的作用程度，并确定其调节声学惊吓阈值的机制。在目标1中，我将分析胡迪尼幼虫是否也对其他感觉形式的刺激过敏，以及它们是否在惊吓调节方面表现出缺陷，如习惯化和脉冲前抑制。我还将测试胡迪尼成年人的过敏性以及焦虑、攻击性和成瘾范例。在目标2中，我将鉴定胡迪尼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。胡迪尼突变体提供了一个令人兴奋的机会，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描述惊吓通路开辟道路，也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.