DISSERTATION RESEARCH: Melatonin Regulation of Vocal Behavior

昼夜节律接近24小时的昼夜循环，使动物的行为和生理与环境线索的周期性变化同步，如光、温度和配偶的可用性。生物节律是如何由荷尔蒙、遗传和神经机制产生的，这引起了极大的科学兴趣。夜间活动的激素褪黑激素在将日常活动带入昼夜循环中起着核心作用。在许多哺乳动物中，活动和交配发生在晚上，因此褪黑激素有可能调节重要的生殖行为，如求偶时使用的发声。本项目将通过回答三个问题来研究夜间活动和高度发声的鱼类--普莱芬鱼(Porichthys Notatus)发声行为的昼夜节律和褪黑激素对发声行为的调节：(1)日常发声节奏是否受到内部昼夜节律的控制？(2)褪黑素是否刺激夜间发声行为？(3)褪黑素是否调节发声脑区神经兴奋性的基因表达？这些研究将有助于建立一个比较框架，用于预测褪黑素对其他物种发声行为的调节，包括表现出不同日常活动模式的鸟类和哺乳动物。更广泛地说，褪黑素与睡眠、时差、自闭症和癫痫有关，这使得关于褪黑素如何影响社交和神经兴奋性的基础研究变得重要和广泛应用。这个项目将测试学员夜间求爱发声受到昼夜节律控制并受到褪黑素刺激的总体假设。拟议的研究将(1)记录自然行为的鱼在持续的外部光线条件下的发声，以测试内部产生的昼夜声音节奏；(2)将褪黑激素植入鱼类，以测试褪黑素对声音行为的调节；以及(3)通过研究褪黑素对具有良好特征的声音网络中神经兴奋性相关基因表达的调节，寻求对褪黑素如何影响声音行为日常节奏的更深入了解。如果学员的日常发声节奏受到内源性昼夜节律的控制，预计在正常光照条件下记录的节奏将在持续的黑暗中持续约24小时。此外，如果海军学员的发声行为依赖于褪黑素的作用，据预测，在恒定的光下发声将减少或消失，这表明消除褪黑素的产生，而在光下外源褪黑素的替代将挽救发声的发生。最后，研究人员预测，褪黑素增加了先前发现的影响神经兴奋性的候选基因的表达。这些基因编码三种类型的离子通道，并在夏夜收集的后脑发声核中表达增加，这是自然发声行为最多的时候。考虑到候选基因的保守功能，这种机制可以为夜间褪黑激素信号的翻译提供分子基础，从而分别在夜间和白天动物中增加或降低神经兴奋性。该项目将培训来自不同背景的现有和新的男女本科生，包括代表人数不足的少数民族。结果将在开放获取的同行评议期刊、在线平台上的流行文章、国家和国际会议以及地方科学宣传活动中传播。

Circadian rhythms that approximate the 24 hr day-night cycle, synchronize animal behavior and physiology to cyclical changes in environmental cues, such as light, temperature, and the availability of mates. How biological rhythms are generated by hormonal, genetic, and neural mechanisms is of great scientific interest. The nocturnal hormone melatonin plays a central role in entraining daily activity to the day-night cycle. In many mammals, activity and mating occur at night so there is potential for melatonin to regulate important reproductive behaviors such as vocalizations used in courtship. This project will investigate circadian and melatonin regulation of daily rhythms in the vocal behavior of a nocturnally active and highly vocal fish, the plainfin midshipman (Porichthys notatus) by answering three questions: (1) Is the daily vocal rhythm under internal, circadian control? (2) Does melatonin stimulate nocturnal vocal behavior? (3) Does melatonin regulate gene expression underlying neural excitability in vocal brain regions? These studies will contribute to a comparative framework for predicting melatonin regulation of vocal behavior in other species, including birds and mammals that exhibit divergent daily activity patterns. More broadly, melatonin has been implicated in sleep, jetlag, autism and epilepsy, making basic research on how it affects social communication and neural excitability important and widely applicable. This project will test the overall hypothesis that the midshipman's nocturnal courtship vocalization is under circadian control and stimulated by melatonin. Proposed studies will (1) record vocalizations from naturally behaving fish under constant external light conditions to test for an internally generated circadian vocal rhythm, (2) implant fish with melatonin to test for melatonin regulation of vocal behavior, and (3) seek a deeper understanding of how melatonin influences daily rhythms in vocal behavior by examining its regulation of neural excitability-related gene expression in a well-characterized vocal network. If the midshipman daily vocal rhythm is under endogenous circadian control, it is predicted that rhythms recorded under a normal light regime will persist under constant darkness with a period of ~24 hr. Additionally, if midshipman vocal behavior is dependent on melatonin action, it is predicted that vocalizations will be reduced or abolished under constant light, shown to abolish melatonin production, while exogenous melatonin replacement under light will rescue the occurrence of vocalizations. Finally, the researchers predict that melatonin increases the expression of previously identified candidate genes known to affect neural excitability. These genes encode three types of ion channels and exhibit increased expression in a hindbrain vocal nucleus collected during the summer night, a time of maximal natural vocal behavior. Given conserved functions of the candidate genes explored in this proposal, such mechanisms could provide the molecular basis for translating the nocturnal melatonin signal to increase or decrease neural excitability in nocturnal versus diurnal animals, respectively. This project will train current and new undergraduates of both genders from diverse backgrounds, including underrepresented minorities. The results will be disseminated in open-access peer-reviewed journals, popular articles via online platforms, at national and international conferences, and at local science outreach events.