Ichinose Tomomi, Hellmer Chase B
Department of Anatomy and Cell Biology, Wayne State University School of Medicine, Detroit, MI 48201, USA.
Department of Ophthalmology, Wayne State University School of Medicine, Detroit, MI 48201, USA.
J Physiol. 2016 Feb 15;594(4):883-94. doi: 10.1113/JP271458. Epub 2015 Dec 20.
Using whole-cell clamp methods, we characterized the temporal coding in each type of OFF bipolar cell. We found that type 2 and 3a cells are transient, type 1 and 4 cells are sustained, and type 3b cells are intermediate. The light-evoked excitatory postsynaptic potentials in some types were rectified, suggesting that they provide inputs to the non-linear ganglion cells. Visual signalling from the photoreceptors was mediated exclusively through the kainate receptors in the transient OFF bipolar cells, whereas both kainate and AMPA receptors contributed in the other cells. This study demonstrates, for the first time, that parallel visual encoding starts at the OFF bipolar cells in a type-specific manner.
The retina is the entrance to the visual system, which receives various kinds of image signals and forms multiple encoding pathways. The second-order retinal neurons, the bipolar cells, are thought to initiate multiple neural streams by encoding various visual signals in different types of cells. However, the functions of each bipolar cell type have not been fully understood. We investigated whether OFF bipolar cells encode visual signals in a type-dependent manner. We recorded the changes in the bipolar cell voltage in response to two input functions: step and sinusoidal light stimuli. Type 1 and 4 OFF bipolar cells were sustained cells and responded to sinusoidal stimuli over a broad range of frequencies. Type 2 and 3a cells were transient and exhibited band-pass filtering. Type 3b cells were in the middle of these two groups. The distinct temporal responses might be attributed to different types of glutamate receptors. We examined the AMPA and kainate glutamate receptor composition in each bipolar cell type. The light responses in the transient OFF bipolar cells were exclusively mediated by kainate receptors. Although the kainate receptors mediated the light responses in the sustained cells, the AMPA receptors also mediated a portion of the responses in sustained cells. Furthermore, we found that some types of cells were rectified more than other types. Taken together, we found that the OFF bipolar cells encode diverse temporal image signals in a type-dependent manner, confirming that each type of OFF bipolar cell initiates diverse temporal visual processing in parallel.
我们使用全细胞膜片钳方法，对每种类型的 OFF 双极细胞中的时间编码进行了表征。我们发现，2 型和 3a 型细胞是瞬态的，1 型和 4 型细胞是持续的，而 3b 型细胞则介于两者之间。某些类型的光诱发兴奋性突触后电位是整流的，这表明它们为非线性神经节细胞提供输入。来自光感受器的视觉信号仅通过瞬态 OFF 双极细胞中的海人酸受体介导，而在其他细胞中海人酸和 AMPA 受体均起作用。这项研究首次证明，平行视觉编码以特定类型的方式在 OFF 双极细胞处开始。
视网膜是视觉系统的入口，它接收各种图像信号并形成多种编码途径。视网膜的二级神经元，即双极细胞，被认为通过在不同类型的细胞中编码各种视觉信号来启动多条神经流。然而，每种双极细胞类型的功能尚未完全了解。我们研究了 OFF 双极细胞是否以类型依赖的方式编码视觉信号。我们记录了双极细胞电压对两种输入函数（阶跃和正弦光刺激）的变化。1 型和 4 型 OFF 双极细胞是持续细胞，在很宽的频率范围内对正弦刺激有反应。2 型和 3a 型细胞是瞬态的，并表现出带通滤波。3b 型细胞处于这两组之间。不同的时间反应可能归因于不同类型的谷氨酸受体。我们检查了每种双极细胞类型中的 AMPA 和海人酸谷氨酸受体组成。瞬态 OFF 双极细胞中的光反应仅由海人酸受体介导。虽然海人酸受体介导持续细胞中的光反应，但 AMPA 受体也介导持续细胞中的部分反应。此外，我们发现某些类型的细胞比其他类型的细胞整流更多。综上所述，我们发现 OFF 双极细胞以类型依赖的方式编码多样的时间图像信号，证实每种类型的 OFF 双极细胞并行启动多样的时间视觉处理。
