Gahtan Ethan, Tanger Paul, Baier Herwig
Department of Psychology, University of Massachusetts, Amherst, Massachusetts 01003, USA.
J Neurosci. 2005 Oct 5;25(40):9294-303. doi: 10.1523/JNEUROSCI.2678-05.2005.
Many vertebrates are efficient hunters and recognize their prey by innate neural mechanisms. During prey capture, the internal representation of the prey's location must be constantly updated and made available to premotor neurons that convey the information to spinal motor circuits. We studied the neural substrate of this specialized visuomotor system using high-speed video recordings of larval zebrafish and laser ablations of candidate brain structures. Seven-day-old zebrafish oriented toward, chased, and consumed paramecia with high accuracy. Lesions of the retinotectal neuropil primarily abolished orienting movements toward the prey. Wild-type fish tested in darkness, as well as blind mutants, were impaired similarly to tectum-ablated animals, suggesting that prey capture is mainly visually mediated. To trace the pathway further, we examined the role of two pairs of identified reticulospinal neurons, MeLc and MeLr, located in the nucleus of the medial longitudinal fasciculus of the tegmentum. These two neurons extend dendrites into the ipsilateral tectum and project axons into the spinal cord. Ablating MeLc and MeLr bilaterally impaired prey capture but spared several other behaviors. Ablating different sets of reticulospinal neurons did not impair prey capture, suggesting a selective function of MeLr and MeLc in this behavior. Ablating MeLc and MeLr neurons unilaterally in conjunction with the contralateral tectum also mostly abolished prey capture, but ablating them together with the ipsilateral tectum had a much smaller effect. These results suggest that MeLc and MeLr function in series with the tectum, as part of a circuit that coordinates prey capture movements.
许多脊椎动物都是高效的猎手，通过先天的神经机制识别猎物。在捕食过程中，猎物位置的内部表征必须不断更新，并提供给运动前神经元，这些神经元将信息传递到脊髓运动回路。我们使用斑马鱼幼体的高速视频记录和对候选脑结构的激光消融，研究了这种特殊视觉运动系统的神经基础。7天大的斑马鱼能够高精度地朝向、追逐并捕食草履虫。视网膜顶盖神经纤维网的损伤主要消除了对猎物的定向运动。在黑暗中测试的野生型鱼以及失明突变体，与顶盖切除的动物表现相似，这表明捕食主要由视觉介导。为了进一步追踪该通路，我们研究了位于脑桥内侧纵束核中的两对已识别的网状脊髓神经元MeLc和MeLr的作用。这两个神经元将树突延伸到同侧顶盖，并将轴突投射到脊髓。双侧消融MeLc和MeLr会损害捕食行为，但不影响其他几种行为。消融不同组的网状脊髓神经元不会损害捕食行为，这表明MeLr和MeLc在这种行为中具有选择性功能。单侧消融MeLc和MeLr神经元并结合对侧顶盖，也大多会消除捕食行为，但将它们与同侧顶盖一起消融的影响要小得多。这些结果表明，MeLc和MeLr与顶盖串联起作用，是协调捕食运动的回路的一部分。
