Liu X B, Honda C N, Jones E G
Department of Anatomy and Neurobiology, University of California, Irvine 92717.
J Comp Neurol. 1995 Jan 30;352(1):69-91. doi: 10.1002/cne.903520106.
This study was aimed at providing quantitative data on the thalamic circuitry that underlies the central processing of somatosensory information. Four physiologically identified thalamocortical relay neurons in the ventral posterior lateral nucleus (VPL) of the cat thalamus were injected with horseradish peroxidase and subjected to quantitative electron microscopy after pre- or postembedding immunostaining for gamma-aminobutyric acid to reveal synaptic terminals of thalamic inhibitory neurons. The four cells all had rapidly adapting responses to light mechanical stimuli applied to their receptive fields, which were situated on hairy or glabrous skin or related to a joint. Their dendritic architecture was typical of cells previously described as type I relay cells in VPL, and they lacked dendritic appendages. Terminals ending in synapses on the injected cells were categorized as RL (ascending afferent), F (inhibitory), PSD (presynaptic dendrite), and RS (mainly corticothalamic) types and were quantified in reconstructions of serial thin sections. RL and F terminals formed the majority of the synapses on proximal dendrites (approximately 50% each). The number of synapses formed by RL terminals declined on intermediate dendrites, but those formed by F terminals remained relatively high, declining to moderate levels (20-30%) on distal dendrites. RS terminals formed moderate numbers of the synapses on intermediate dendrites and the majority (> 60%) of the synapses on distal dendrites. Synapses formed by PSDs were concentrated on intermediate dendrites and were few in number (approximately 6%). They formed synaptic triads with F terminals and rarely with RL terminals. On somata, only a few synapses were found, all made by F terminals. The total number of synapses per cell was calculated to be 5,584-8,797, with a density of 0.6-0.9 per micrometer of dendritic length. Of the total, RL terminals constituted approximately 15%, F terminals approximately 35%, PSD terminals approximately 5%, and RS terminals approximately 50%. These results provide the first quantitative assessment of the synaptic architecture of thalamic somatic sensory relay neurons and show the basic organizational pattern exhibited by representatives of the physiological type of relay neurons most commonly encountered in the VPL nucleus.
本研究旨在提供有关丘脑回路的定量数据，该回路是躯体感觉信息中枢处理的基础。对猫丘脑腹后外侧核（VPL）中四个经生理学鉴定的丘脑皮质中继神经元注射辣根过氧化物酶，并在对γ-氨基丁酸进行包埋前或包埋后免疫染色以显示丘脑抑制性神经元的突触终末后，进行定量电子显微镜观察。这四个细胞对施加于其位于有毛或无毛皮肤或与关节相关的感受野的轻机械刺激均具有快速适应性反应。它们的树突结构是先前描述的VPL中I型中继细胞的典型结构，且缺乏树突附属物。在注射细胞上形成突触的终末被分类为RL（上行传入）、F（抑制性）、PSD（突触前树突）和RS（主要是皮质丘脑）类型，并在连续薄切片重建中进行定量。RL和F终末在近端树突上形成了大部分突触（各约占50%）。RL终末在中间树突上形成的突触数量减少，但F终末形成的突触数量仍相对较高，在远端树突上降至中等水平（20 - 30%）。RS终末在中间树突上形成中等数量的突触，在远端树突上形成大部分突触（> 60%）。PSD形成的突触集中在中间树突上，数量很少（约6%）。它们与F终末形成突触三联体，很少与RL终末形成。在胞体上，仅发现少数突触，均由F终末形成。每个细胞的突触总数计算为5584 - 8797个，树突长度每微米的密度为0.6 - 0.9个。其中，RL终末约占15%，F终末约占35%，PSD终末约占5%，RS终末约占50%。这些结果首次对丘脑躯体感觉中继神经元的突触结构进行了定量评估，并展示了VPL核中最常见的中继神经元生理类型代表所呈现的基本组织模式。
