Electrosensory processing in plankton capture by the paddlefish

首席研究员Lon A.Wilkens在浮游生物捕获的浮游生物中的电感觉处理电感觉是古代鱼类的一种特殊感觉方式，最为人所知的是鲨鱼，它能够近距离探测潜在猎物的电场并使用电磁场进行导航。尽管这些都是电感的宏观功能，但淡水白对虾的电感系统最近被证明能探测到微小浮游生物的微弱电场，浮游生物是鱼类的主要食物来源。这种新的感觉系统的电感受器存在于一个细长的嘴上，长度是鱼的三分之一，这构成了一个相当于天线的电感觉器官。这个器官的高度敏感性及其在以浮游猎物为目标的行为中的作用使其成为研究环境中空间特征的感觉加工的有用的模型准备。重要的是，大脑包含一个很大的、容易区分的区域，非常适合探索构成摄食行为基础的神经处理。威尔肯斯博士在这项研究计划中的目标是阐明神经回路和算法，使白鳍鱼能够选择性地瞄准在浑浊的水柱中漂流的单个浮游生物。威尔肯斯博士将研究来自嘴上感受器的感觉纤维的电信号特性，以及这些纤维在后脑区域接触的神经元的特性，即首先处理电感觉信息的背侧八腹侧核(DON)。最初的实验将调查感官输入到DON的组织。在其他动物的感觉系统中，通常有一种外周感受场的地形图表示，绘制在它们大脑中的目标细胞上，这样相邻的脑细胞就对应于附近的感受场。然而，早期的生理记录并没有在白鳍鱼的大脑中发现这种地形图的证据。为了进一步研究这一不同寻常的特征，威尔肯斯博士将使用组织学染色技术，追踪感觉纤维进入大脑的神经投射。这将为大脑中电感觉处理的组织提供直接的神经解剖学证据。如果证实没有地形组织，则肯定存在其他提取空间特征的机制。先前记录的DON内神经细胞的神经冲动活动表明，它们的放电率反映了电感觉刺激波形的一阶导数。因此，脑细胞优先对刺激信号的动态特征做出反应，而不是对其大小做出反应。由于解剖学数据可能会证实DON中不存在空间地形，威尔肯斯博士开发了一种导数过滤器的计算机模拟模型，通过该模型，环境信号的距离和速度信息可以编码在DON的反应神经元中。该模型将通过在鱼嘴上的感受场上移动的电刺激进行测试，从而模拟鱼在正常游泳过程中遇到的浮游电场。在对这些细胞进行记录之后，将注入神经染色，以追踪它们向中脑高级区域的投射。据推测，在中脑DON细胞的终末投射中将建立地形图表征。威尔肯斯博士对白鳍鱼电感的描述对这种受威胁物种的渔业管理具有广泛的影响，除了成为研究大脑功能的重要模型系统外，还解释了为什么鱼类避免在河流中建造金属结构(水坝)。威尔肯斯博士将积极招募来自圣路易斯市区的代表性不足的学生参与这个项目。

Electrosensory Processing in plankton capture by the paddlefishLon A. Wilkens, Principal InvestigatorThe electrosense is a specialized sensory modality of ancient fish and is best known in sharks that are able to detect the electrical fields of potential prey at close range and to use electromagnetic fields for navigation. Whereas these are macroscopic functions of the electrosense, the electrosensory system in the freshwater paddlefish has recently been shown to detect the weak electric fields of tiny plankton, the primary food source for the fish. The electroreceptors of this novel sensory system are present on an elongated rostrum, one-third the length of the fish, which constitutes an electrosensory organ the equivalent of an antenna. The exquisite sensitivity of this organ and its behavioral role in targeting planktonic prey makes it a useful model preparation in which to investigate the sensory processing of spatial features in the environment. Importantly, the brain contains a large, easily distinguishable region that is well suited for exploring the neural processing that underlies the feeding behavior. Dr. Wilkens' objective in this research proposal is to elucidate the neural circuitry and algorithms that enable the paddlefish to selectively target single plankton adrift in the turbid water column. Dr. Wilkens will study the electric signaling properties of sensory fibers coming from the receptors on the rostrum and the properties of neurons that the fibers contact in the hindbrain region, the dorsal octavolateralis nucleus (DON), which first processes the electrosensory information. Initial experiments will investigate the organization of sensory input into the DON. In sensory systems from other animals there is typically a topographic representation of peripheral receptive fields mapped out onto their target cells in the brain, such that adjacent brain cells correspond to nearby receptive fields. Early physiological recordings, however, have found no evidence for such topography in the paddlefish brain. To further investigate this unusual feature, Dr. Wilkens will use histological staining techniques that trace the nerve projections of the sensory fibers into the brain. This will provide direct neuroanatomical evidence for the organization of electrosensory processing in the brain.If it is confirmed that there is no topographical organization, other mechanisms for extracting spatial features must exist. Previous records of neural impulse activity from nerve cells in the DON show that their firing rates reflect the first derivative of an electrosensory stimulus waveform. Thus, brain cells respond preferentially to dynamical features of the stimulus signal, rather than to its magnitude. With the possibility that anatomical data will confirm the absence of spatial topography in the DON, Dr. Wilkens has developed a computer simulation model of a derivative filter whereby the information about the distance and velocity of an environmental signal could be encoded in the response neurons of the DON. The model will be tested by presenting electrical stimuli that move over the receptive fields in the rostrum, thus simulating the planktonic electric fields encountered by the fish during normal swimming. Recordings from these cells will be followed by the injection of nerve stains to trace their projections into higher midbrain regions. It is hypothesized that topographic representation will be established in the terminal projections of DON cells in the midbrain. Dr. Wilkens' descriptions of the electrosense in paddlefish has had broad implications for fisheries management of this threatened species, providing an explanation for why fish avoid metal structures (dams) in the rivers in addition to becoming an important model system for studying brain function. Dr. Wilkens will actively recruit underrepresented students from the St. Louis urban region to participate in this project.