Department of Neurophysiology, Nara Medical University, Kashihara, Nara, Japan.
J Neurophysiol. 2023 Feb 1;129(2):399-409. doi: 10.1152/jn.00452.2022. Epub 2023 Jan 18.
The prepositus hypoglossi nucleus (PHN) and the interstitial nucleus of Cajal (INC) are involved in controlling horizontal and vertical gaze, respectively. Previous studies have shown that PHN neurons exhibit depolarized or hyperpolarized responses to serotonin (5-hydroxytryptamine, 5-HT). However, serotonergic modulation of INC neurons has not been examined. Furthermore, the relationship between 5-HT-induced responses and neuron types based on neurotransmitter phenotypes has not been clarified. In this study, we investigated 5-HT-induced current responses in PHN and INC neurons and the distributions of distinct current responses in different neuron types, using whole cell recordings of wild-type and transgenic rat brain stem slices. Local application of 5-HT to the cell soma confirmed that slow inward (SI) and slow outward (SO) currents were mediated by 5-HT and 5-HT receptors, respectively. Furthermore, fast inward (FI) currents that were mediated by 5-HT receptors were observed. These three current responses were observed in both PHN and INC neurons. Analyses of the distributions of the three current responses revealed that fluorescently identified glutamatergic and inhibitory neurons in the PHN showed high proportions of SI and SO currents, respectively, whereas glutamatergic and inhibitory neurons in the INC showed mainly SO currents. When PHN and INC neurons were characterized on the basis of firing patterns, the proportions of the currents depended on the firing patterns. The different distributions of 5-HT-induced currents suggest distinct serotonergic modulation modes specific to horizontal and vertical gaze control. Serotonergic modulation of vertical gaze control (interstitial nucleus of Cajal, INC) is less understood than that of horizontal gaze control (prepositus hypoglossal nucleus, PHN). Here, we report 5-HT-induced fast inward currents in addition to the previously reported slow inward and outward currents. The distributions of these currents in INC neurons based on neurotransmitter phenotypes differ from those in PHN neurons. These results suggest distinct serotonergic modulation modes in horizontal and vertical gaze control centers.
动眼神经前置核（PHN）和 Cajal 间质核（INC）分别参与控制水平和垂直眼球运动。先前的研究表明，PHN 神经元对 5-羟色胺（5-羟色胺，5-HT）表现出去极化或超极化反应。然而，尚未检查 INC 神经元的 5-羟色胺调制。此外，基于神经递质表型的 5-HT 诱导反应与神经元类型之间的关系尚未阐明。在这项研究中，我们使用野生型和转基因大鼠脑干切片的全细胞膜片钳记录，研究了 PHN 和 INC 神经元中 5-HT 诱导的电流反应以及不同神经元类型中不同电流反应的分布。5-HT 向细胞体的局部应用证实，慢内向（SI）和慢外向（SO）电流分别由 5-HT 和 5-HT 受体介导。此外，还观察到由 5-HT 受体介导的快速内向（FI）电流。这三种电流反应均在 PHN 和 INC 神经元中观察到。三种电流反应分布的分析表明，PHN 中荧光鉴定的谷氨酸能和抑制性神经元分别表现出高比例的 SI 和 SO 电流，而 INC 中的谷氨酸能和抑制性神经元主要表现出 SO 电流。当根据放电模式对 PHN 和 INC 神经元进行特征描述时，电流的比例取决于放电模式。5-HT 诱导电流的不同分布表明，水平和垂直眼球控制的特定的 5-羟色胺调制模式不同。与水平眼球控制（动眼神经前置核，PHN）相比，垂直眼球控制（Cajal 间质核，INC）的 5-羟色胺调制作用了解较少。在这里，我们除了先前报道的慢内向和外向电流外，还报告了 5-HT 诱导的快速内向电流。基于神经递质表型的这些电流在 INC 神经元中的分布与 PHN 神经元中的分布不同。这些结果表明水平和垂直眼球控制中心存在不同的 5-羟色胺调制模式。
