Department of Endocrine Neurobiology, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary.
Medical Gene Technology Unit, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary.
Thyroid. 2019 Dec;29(12):1858-1868. doi: 10.1089/thy.2019.0357. Epub 2019 Dec 6.
Glycine is a classical neurotransmitter that has role in both inhibitory and excitatory synapses. To understand whether glycinergic inputs are involved in the regulation of the hypophysiotropic thyrotropin-releasing hormone (TRH) neurons, the central controllers of the hypothalamic-pituitary-thyroid axis, the glycinergic innervation of the TRH neurons was studied in the hypothalamic paraventricular nucleus (PVN). Double-labeling immunocytochemistry and patch-clamp electrophysiology were used to determine the role of glycinergic neurons in the regulation of TRH neurons in the PVN. Anterograde and retrograde tracing methods were used to determine the sources of the glycinergic input of TRH neurons. Glycine transporter-2 (GLYT2), a marker of glycinergic neurons, containing axons were found to establish symmetric type of synapses on TRH neurons in the PVN. Furthermore, glycine receptor immunoreactivity was observed in these TRH neurons. The raphe magnus (RMg) and the ventrolateral periaqueductal gray (VLPAG) were found to be the exclusive sources of the glycinergic innervation of the TRH neurons within the PVN. Patch-clamp electrophysiology using sections of TRH-IRES-tdTomato mice showed that glycine hyperpolarized the TRH neurons and completely blocked the firing of these neurons. Glycine also markedly hyperpolarized the TRH neurons in the presence of tetrodotoxin demonstrating the direct effect of glycine. In more than 60% of the TRH neurons, spontaneous inhibitory postsynaptic currents (sIPSCs) were observed, even after the pharmacological inhibition of glutamatergic and GABAergic neuronal transmission. The glycine antagonist, strychnine, almost completely abolished these sIPSCs, demonstrating the inhibitory nature of the glycinergic input of TRH neurons. These data demonstrate that TRH neurons in the PVN receive glycinergic inputs from the RMg and the VLPAG. The symmetric type of synaptic connection and the results of the electrophysiological experiments demonstrate the inhibitory nature of these inputs.
甘氨酸是一种经典的神经递质，在抑制性和兴奋性突触中都有作用。为了了解甘氨酸能输入是否参与了下丘脑-垂体-甲状腺轴的下丘脑促甲状腺素释放激素（TRH）神经元的调节，研究了下丘脑室旁核（PVN）中 TRH 神经元的甘氨酸能传入。使用双标记免疫细胞化学和膜片钳电生理学来确定 PVN 中 TRH 神经元中甘氨酸能神经元在调节 TRH 神经元中的作用。使用顺行和逆行示踪方法来确定 TRH 神经元甘氨酸能输入的来源。发现含有轴突的甘氨酸转运体-2（GLYT2），作为甘氨酸能神经元的标志物，在 PVN 中的 TRH 神经元上建立了对称型的突触。此外，在这些 TRH 神经元中观察到甘氨酸受体免疫反应性。发现中缝大核（RMg）和腹外侧导水管周围灰质（VLPAG）是 PVN 中 TRH 神经元甘氨酸能传入的唯一来源。使用 TRH-IRES-tdTomato 小鼠切片的膜片钳电生理学显示，甘氨酸使 TRH 神经元超极化，并完全阻断这些神经元的放电。甘氨酸也明显使 TRH 神经元超极化，在存在河豚毒素的情况下，证明了甘氨酸的直接作用。在超过 60%的 TRH 神经元中，观察到自发性抑制性突触后电流（sIPSCs），即使在谷氨酸能和 GABA 能神经元传递的药理学抑制后也是如此。甘氨酸拮抗剂士的宁几乎完全消除了这些 sIPSCs，证明了 TRH 神经元甘氨酸能传入的抑制性质。这些数据表明，PVN 中的 TRH 神经元接收来自 RMg 和 VLPAG 的甘氨酸能输入。对称型突触连接和电生理实验的结果表明了这些输入的抑制性质。
