■在视网膜神经节细胞处引起的视觉信号被各种突触输入修饰和调节,这些突触输入在发送到皮质之前撞击外侧膝状核细胞。膝状输入用于在膝状细胞类型的离散树突状片段上聚类或形成微电路的选择性,可以为膝状电路的网络特性和通过并行视觉途径的差分信号处理提供结构基础。在我们的研究中,我们旨在揭示小鼠外侧膝状核中形态学上可辨别的中继细胞类型和中间神经元的输入选择性模式。
■我们使用了两组扫描Blockface电子显微镜(SBEM)图像堆栈和Reconstruct软件来手动重建末端boutons和枝晶段。首先,使用无偏终端抽样(UTS)方法和统计建模,我们确定了基于体积将膝状boutons分类为其推定来源的标准。根据先前描述的线粒体形态,在视网膜和非视网膜类别中分类的膝状末端结。可以根据它们的布顿体积分布进一步分为多个亚群。根据形态学标准,被认为是非视网膜的终端由五个不同的亚群组成,包括小尺寸的假定的皮质丘脑和胆碱能boutons,两个中等大小的推定GABA能输入,和含有深色线粒体的大型布顿类型。视网膜末端也由四个不同的亚群组成。然后将这些亚群的截止标准应用于在中继细胞或中间神经元的重建树突段上突触的末端数据集。
■使用网络分析方法,我们发现,在假定的X型细胞树突节段上,视网膜和皮质末端几乎完全分离,其特征是葡萄样附件和三联体。在这些细胞上,神经元间附属物与视网膜和其他中等大小的末端混合在一起,在肾小球内形成三联体。相比之下,第二个,假定的Y型细胞显示树突状斑点贴壁,并接受所有末端类型,而对突触位置没有选择性;这些不参与三联体。此外,X-接受的视网膜和皮质突触的贡献,Y-和中间神经元树突不同,因此超过60%的输入到中间神经元树突来自视网膜,与X型和Y型细胞的20%和7%相反,分别。
■结果是来自膝状细胞类型的不同起源的突触输入的网络特性差异的基础。
UNASSIGNED: The visual signals evoked at the retinal ganglion cells are modified and modulated by various synaptic inputs that impinge on lateral geniculate nucleus cells before they are sent to the cortex. The selectivity of geniculate inputs for clustering or forming microcircuits on discrete dendritic segments of geniculate cell types may provide the structural basis for network properties of the geniculate circuitry and differential signal processing through the parallel pathways of vision. In our study, we aimed to reveal the patterns of input selectivity on morphologically discernable relay cell types and interneurons in the mouse lateral geniculate nucleus.
UNASSIGNED: We used two sets of Scanning Blockface Electron Microscopy (
SBEM) image stacks and Reconstruct software to manually reconstruct of terminal boutons and dendrite segments. First, using an unbiased terminal sampling (UTS) approach and statistical modeling, we identified the criteria for volume-based sorting of geniculate boutons into their putative origins. Geniculate terminal boutons that were sorted in retinal and non-retinal categories based on previously described mitochondrial morphology, could further be sorted into multiple subpopulations based on their bouton volume distributions. Terminals deemed non-retinal based on the morphological criteria consisted of five distinct subpopulations, including small-sized putative corticothalamic and cholinergic boutons, two medium-sized putative GABAergic inputs, and a large-sized bouton type that contains dark mitochondria. Retinal terminals also consisted of four distinct subpopulations. The cutoff criteria for these subpopulations were then applied to datasets of terminals that synapse on reconstructed dendrite segments of relay cells or interneurons.
UNASSIGNED: Using a network analysis approach, we found an almost complete segregation of retinal and cortical terminals on putative X-type cell dendrite segments characterized by grape-like appendages and triads. On these cells, interneuron appendages intermingle with retinal and other medium size terminals to form triads within glomeruli. In contrast, a second, presumed Y-type cell displayed dendrodendritic puncta adherentia and received all terminal types without a selectivity for synapse location; these were not engaged in triads. Furthermore, the contribution of retinal and cortical synapses received by X-, Y- and interneuron dendrites differed such that over 60% of inputs to interneuron dendrites were from the retina, as opposed to 20% and 7% to X- and Y-type cells, respectively.
UNASSIGNED: The results underlie differences in network properties of synaptic inputs from distinct origins on geniculate cell types.