FACILITATION AND INHIBITION IN DIRECTIONAL SELECTIVITY

定向选择性背后的细胞学机制 许多物种的视网膜神经节细胞目前还知之甚少。 一种假说假定这种方向性是由于 神经节细胞的空间不对称抑制性输入。 这种不对称的输入将阻止对 空方向，但不会阻止首选方向 回应。另一种假设假设首选-空 分化发生在无长突细胞的树突中，它 然后将这些信息传递给神经节细胞。这些树突 将提供空间不对称的兴奋性输入到 神经节细胞。枝晶中的非线性过程会产生 零方向抑制和促进对 优先方向的运动。神经递质GABA被认为 以调节两种假说中的抑制作用。这项拨款建议 描述了三个将仔细研究这两个问题的实验 假设。实验将定向地使用开-关 乌龟和兔子的选择性神经节细胞。 1)第一个实验将测试GABA能抑制是否通过 GABA-A受体是定向选择性所必需的。 2)第二个实验将测试直接神经节细胞 抑制是定向选择性所必需的。 3)第三个实验将确定兴奋性 感受野反映了空间的不对称性 定向选择性。 这个项目应该有助于理解如何 生物物理机制是定向选择性的基础。 此外，视网膜方向选择性的研究将具有 对眼动控制的理解产生了影响。

The cellular mechanism underlying the directional selectivity of retinal ganglion cells in many species is as yet poorly understood. A hypothesis postulates that this directionality is due to a spatially-asymmetric inhibitory input onto the ganglion cells. This asymmetric input would prevent responses to motions in the null-direction, but would not prevent preferred-direction responses. An alternative hypothesis assumes that preferred-null discrimination occurs in the dendrites of amacrine cells, which then relay this information to ganglion cells. These dendrites would provide a spatially asymmetric excitatory input onto the ganglion cell. Nonlinear processes in the dendrites would produce null-direction inhibition and facilitation of the responses to preferred-direction motions. The neurotransmitter GABA is believed to mediate the inhibition in both hypotheses. This grant proposal describes three experiments that will scrutinize these two hypotheses. The experiments will use ON-OFF directionally selective ganglion cells of turtles and rabbits. 1) The first experiment will test whether GABAergic inhibition via GABA-A receptors is necessary for directional selectivity. 2) The second experiment will test whether direct ganglion-cell inhibition is necessary for directional selectivity. 3) The third experiment will determine whether the excitatory receptive field reflects the spatial asymmetry necessary for directional selectivity. This project should contribute to the understanding of how biophysical mechanisms underlie directional selectivity. Furthermore, the study of retinal directional selectivity will have an impact on the understanding of eye-movement control.