Peron Simon P, Krapp Holger G, Gabbiani Fabrizio
Department of Neuroscience, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
J Neurophysiol. 2007 Jan;97(1):159-77. doi: 10.1152/jn.00660.2006. Epub 2006 Oct 4.
The lobula giant movement detector (LGMD) is a visual interneuron of Orthopteran insects involved in collision avoidance and escape behavior. The LGMD possesses a large dendritic field thought to receive excitatory, retinotopic projections from the entire compound eye. We investigated whether the LGMD's receptive field for local motion stimuli can be explained by its electrotonic structure and the eye's anisotropic sampling of visual space. Five locust (Schistocerca americana) LGMD neurons were stained and reconstructed. We show that the excitatory dendritic field and eye can be fitted by ellipsoids having similar geometries. A passive compartmental model fit to electrophysiological data was used to demonstrate that the LGMD is not electrotonically compact. We derived a spike rate to membrane potential transform using intracellular recordings under visual stimulation, allowing direct comparison between experimental and simulated receptive field properties. By assuming a retinotopic mapping giving equal weight to each ommatidium and equally spaced synapses, the model reproduced the experimental data along the eye equator, though it failed to reproduce the receptive field along the ventral-dorsal axis. Our results illustrate how interactions between the distribution of synaptic inputs and the electrotonic properties of neurons contribute to shaping their receptive fields.
小叶巨型运动探测器（LGMD）是直翅目昆虫的一种视觉中间神经元，参与避撞和逃逸行为。LGMD拥有一个大的树突场，被认为接收来自整个复眼的兴奋性、视网膜拓扑投射。我们研究了LGMD对局部运动刺激的感受野是否可以由其电紧张结构和眼睛对视觉空间的各向异性采样来解释。对五只美洲沙漠蝗（Schistocerca americana）的LGMD神经元进行了染色和重建。我们表明，兴奋性树突场和眼睛可以由具有相似几何形状的椭球体拟合。使用拟合电生理数据的被动隔室模型来证明LGMD在电紧张方面并非紧密。我们通过在视觉刺激下的细胞内记录得出了放电频率与膜电位的转换关系，从而能够直接比较实验和模拟的感受野特性。通过假设一种视网膜拓扑映射，给予每个小眼同等权重且突触等距分布，该模型再现了沿眼赤道的实验数据，尽管它未能再现沿腹 - 背轴的感受野。我们的结果说明了突触输入分布与神经元电紧张特性之间的相互作用如何有助于塑造它们的感受野。
