Department of Anatomy and Neurobiology, School of Medicine and Dentistry, Kyungpook National University, 188-1, 2-Ga, Samdeok-Dong, Jung-Gu, Daegu, 700-412, South Korea.
Korea Brian Research Institute, 61 Cheomdan-ro, Dong-gu, Daegu, 701-300, South Korea.
Brain Struct Funct. 2018 Jun;223(5):2259-2268. doi: 10.1007/s00429-018-1607-3. Epub 2018 Feb 19.
The neurons in the trigeminal mesencephalic nucleus (Vmes) innervate jaw-closing muscle spindles and periodontal ligaments, and play a crucial role in the regulation of jaw movements. Recently, it was shown that many boutons that form synapses on them are immunopositive for glycine (Gly+), suggesting that these neurons receive glycinergic input. Information about the glycine receptors that mediate this input is needed to help understand the role of glycine in controlling Vmes neuron excitability. For this, we investigated the expression of glycine receptor subunit alpha 3 (GlyRα3) and gephyrin in neurons in Vmes and the trigeminal motor nucleus (Vmo), and the Gly+ boutons that contact them by light- and electron-microscopic immunocytochemistry and quantitative ultrastructural analysis. The somata of the Vmes neurons were immunostained for GlyRα3, but not gephyrin, indicating expression of homomeric GlyR. The immunostaining for GlyRα3 was localized away from the synapses in the Vmes neuron somata, in contrast to the Vmo neurons, where the staining for GlyRα3 and gephyrin were localized at the subsynaptic zones in somata and dendrites. Additionally, the ultrastructural determinants of synaptic strength, bouton volume, mitochondrial volume, and active zone area, were significantly smaller in Gly+ boutons on the Vmes neurons than in those on the Vmo neurons. These findings support the notion that the Vmes neurons receive glycinergic input via putative extrasynaptic homomeric glycine receptors, likely mediating a slow, tonic modulation of the Vmes neuron excitability.
三叉神经中脑核（Vmes）中的神经元支配下颌闭合肌梭和牙周韧带，在调节下颌运动中发挥着关键作用。最近的研究表明，许多与它们形成突触的终扣是甘氨酸（Gly+）免疫阳性的，这表明这些神经元接受甘氨酸能输入。为了帮助理解甘氨酸在控制 Vmes 神经元兴奋性中的作用，需要了解介导这种输入的甘氨酸受体的信息。为此，我们通过光和电子显微镜免疫细胞化学和定量超微结构分析，研究了 Vmes 和三叉神经运动核（Vmo）中的神经元中甘氨酸受体亚单位 alpha 3（GlyRα3）和 gephyrin 的表达，以及与之接触的 Gly+终扣。Vmes 神经元的胞体被 GlyRα3 免疫染色，但不被 gephyrin 染色，表明存在同源 GlyR 的表达。GlyRα3 的免疫染色远离 Vmes 神经元胞体中的突触，而与 Vmo 神经元相反，GlyRα3 和 gephyrin 的染色位于胞体和树突的突触下区。此外，Gly+终扣的突触强度、终扣体积、线粒体体积和活性区面积等超微结构决定因素，在 Vmes 神经元上的比在 Vmo 神经元上的显著更小。这些发现支持这样一种观点，即 Vmes 神经元通过假定的 extrasynaptic 同源甘氨酸受体接受甘氨酸能输入，可能介导 Vmes 神经元兴奋性的缓慢、紧张性调节。
