Kovács Adrienn, Pál Balázs
Department of Physiology, Faculty of Medicine, University of Debrecen Debrecen, Hungary.
Front Cell Neurosci. 2017 Feb 1;11:16. doi: 10.3389/fncel.2017.00016. eCollection 2017.
Slow inward currents (SICs) are known as excitatory events of neurons caused by astrocytic glutamate release and consequential activation of neuronal extrasynaptic NMDA receptors. In the present article we investigate the role of these astrocyte-dependent excitatory events on a cholinergic nucleus of the reticular activating system (RAS), the pedunculopontine nucleus (PPN). It is well known about this and other elements of the RAS, that they do not only give rise to neuromodulatory innervation of several areas, but also targets neuromodulatory actions from other members of the RAS or factors providing the homeostatic drive for sleep. Using slice electrophysiology, optogenetics and morphological reconstruction, we revealed that SICs are present in a population of PPN neurons. The frequency of SICs recorded on PPN neurons was higher when the soma of the given neuron was close to an astrocytic soma. SICs do not appear simultaneously on neighboring neurons, thus it is unlikely that they synchronize neuronal activity in this structure. Occurrence of SICs is regulated by cannabinoid, muscarinic and serotonergic neuromodulatory mechanisms. In most cases, SICs occurred independently from tonic neuronal currents. SICs were affected by different neuromodulatory agents in a rather uniform way: if control SIC activity was low, the applied drugs increased it, but if SIC activity was increased in control, the same drugs lowered it. SICs of PPN neurons possibly represent a mechanism which elicits network-independent spikes on certain PPN neurons; forming an alternative, astrocyte-dependent pathway of neuromodulatory mechanisms.
慢内向电流（SICs）是由星形胶质细胞释放谷氨酸并随后激活神经元突触外NMDA受体所引起的神经元兴奋性事件。在本文中，我们研究了这些依赖星形胶质细胞的兴奋性事件在网状激活系统（RAS）的一个胆碱能核团——脚桥核（PPN）中的作用。众所周知，RAS的这个核团以及其他组成部分不仅对多个区域产生神经调节性支配，而且也是RAS其他成员神经调节作用的靶点，或者是为睡眠提供稳态驱动的因素的靶点。通过切片电生理学、光遗传学和形态学重建，我们发现SICs存在于PPN神经元群体中。当给定神经元的胞体靠近星形胶质细胞胞体时，记录到的PPN神经元上SICs的频率更高。SICs不会在相邻神经元上同时出现，因此它们不太可能使该结构中的神经元活动同步。SICs的发生受大麻素、毒蕈碱和5-羟色胺能神经调节机制的调控。在大多数情况下，SICs独立于神经元的强直电流而发生。不同的神经调节药物对SICs的影响方式相当一致：如果对照SIC活性较低，应用药物会使其增加，但如果对照中SIC活性增加，相同的药物会使其降低。PPN神经元的SICs可能代表了一种机制，该机制在某些PPN神经元上引发与网络无关的动作电位；形成一种替代的、依赖星形胶质细胞的神经调节机制途径。
