Ito Tetsufumi, Oliver Douglas L
Department of Anatomy, Faculty of Medical Sciences, University of Fukui, Eiheiji, Fukui, Japan; Research and Education Program for Life Science, University of Fukui, Fukui, Japan.
J Comp Neurol. 2014 Oct 15;522(15):3539-54. doi: 10.1002/cne.23623. Epub 2014 May 21.
Large GABAergic (LG) neurons are a distinct type of neuron in the inferior colliculus (IC) identified by their dense vesicular glutamate transporter 2 (VGLUT2)-containing axosomatic synaptic terminals. Yet the sources of these terminals are unknown. Since IC glutamatergic neurons express VGLUT2, and IC neurons are known to have local collaterals, we tested the hypothesis that these excitatory, glutamatergic axosomatic inputs on LG neurons come from local axonal collaterals and commissural IC neurons. We injected a recombinant viral tracer into the IC which enabled Golgi-like green fluorescent protein (GFP) labeling in both dendrites and axons. In all cases, we found terminals positive for both GFP and VGLUT2 (GFP+/VGLUT2+) that made axosomatic contacts on LG neurons. One to six axosomatic contacts were made on a single LG cell body by a single axonal branch. The GFP-labeled neurons giving rise to the VGLUT2+ terminals on LG neurons were close by. The density of GFP+/VGLUT2+ terminals on the LG neurons was related to the number of nearby GFP-labeled cells. On the contralateral side, a smaller number of LG neurons received axosomatic contacts from GFP+/VGLUT2+ terminals. In cases with a single GFP-labeled glutamatergic neuron, the labeled axonal plexus was flat, oriented in parallel to the fibrodendritic laminae, and contacted 9-30 LG cell bodies within the plexus. Our data demonstrated that within the IC microcircuitry there is a convergence of inputs from local IC excitatory neurons on LG cell bodies. This suggests that LG neurons are heavily influenced by the activity of the nearby laminar glutamatergic neurons in the IC.
大γ-氨基丁酸能（LG）神经元是下丘（IC）中一种独特类型的神经元，其特征是含有密集的、富含囊泡型谷氨酸转运体2（VGLUT2）的轴体突触终末。然而，这些终末的来源尚不清楚。由于IC谷氨酸能神经元表达VGLUT2，且已知IC神经元有局部侧支，我们检验了这样一个假说，即LG神经元上这些兴奋性的、谷氨酸能的轴体输入来自局部轴突侧支和IC连合神经元。我们将一种重组病毒示踪剂注入IC，它能在树突和轴突中实现类似高尔基染色的绿色荧光蛋白（GFP）标记。在所有情况下，我们都发现了同时对GFP和VGLUT2呈阳性（GFP+/VGLUT2+）的终末，它们与LG神经元形成轴体接触。单个轴突分支在单个LG细胞体上形成一到六个轴体接触。产生LG神经元上VGLUT2+终末的GFP标记神经元就在附近。LG神经元上GFP+/VGLUT2+终末的密度与附近GFP标记细胞的数量有关。在对侧，较少数量的LG神经元接受来自GFP+/VGLUT2+终末的轴体接触。在只有单个GFP标记的谷氨酸能神经元的情况下，标记的轴突丛是扁平的，与纤维树突层平行排列，并与丛内9 - 30个LG细胞体接触。我们的数据表明，在IC微回路中，存在来自局部IC兴奋性神经元的输入在LG细胞体上的汇聚。这表明LG神经元受到IC中附近层状谷氨酸能神经元活动的严重影响。
