Zheng Fang, Nixdorf-Bergweiler Barbara E, Edelmann Elke, van Brederode Johannes F M, Alzheimer Christian
Institute of Physiology and Pathophysiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany.
Institut für Physiologie, Otto-von-Guericke-Universität, Magdeburg, Germany.
Front Cell Neurosci. 2020 Jan 9;13:562. doi: 10.3389/fncel.2019.00562. eCollection 2019.
The cholinergic system plays an essential role in central respiratory control, but the underlying mechanisms remain elusive. We used whole-cell recordings in brainstem slices from juvenile mice expressing enhanced green fluorescent protein (EGFP) under the control of the glycine transporter type 2 (GlyT) promoter, to examine muscarinic modulation of morphologically identified glycinergic neurons in the preBötzinger complex (preBötC), an area critical for central inspiratory rhythm generation. Biocytin-filled reconstruction of glycinergic neurons revealed that the majority of them had few primary dendrites and had axons arborized within their own dendritic field. Few glycinergic neurons had axon collaterals extended towards the premotor/motor areas or ran towards the contralateral preBötC, and had more primary dendrites and more compact dendritic trees. Spontaneously active glycinergic neurons fired regular spikes, or less frequently in a "burst-like" pattern at physiological potassium concentration. Muscarine suppressed firing in the majority of regular spiking neurons M receptor activation while enhancing the remaining neurons through M receptors. Interestingly, rhythmic bursting was augmented by muscarine in a small group of glycinergic neurons. In contrast to its heterogeneous modulation of glycinergic neuronal excitability, muscarine generally depressed inhibitory and excitatory synaptic inputs onto both glycinergic and non-glycinergic preBötC neurons, with a stronger effect on inhibitory input. Notably, presynaptic muscarinic attenuation of excitatory synaptic input was dependent on M receptors in glycinergic neurons and on M receptors in non-glycinergic neurons. Additional field potential recordings of excitatory synaptic potentials in the M receptor knockout mice indicate that glycinergic and non-glycinergic neurons contribute equally to the general suppression by muscarine of excitatory activity in preBötC circuits. In conclusion, our data show that preBötC glycinergic neurons are morphologically heterogeneous, and differ in the properties of synaptic transmission and muscarinic modulation in comparison to non-glycinergic neurons. The dominant and cell-type-specific muscarinic inhibition of synaptic neurotransmission and spiking may contribute to central respiratory disturbances in high cholinergic states.
胆碱能系统在中枢呼吸控制中起着至关重要的作用，但其潜在机制仍不清楚。我们使用全细胞膜片钳记录技术，在甘氨酸转运体2（GlyT）启动子控制下表达增强型绿色荧光蛋白（EGFP）的幼年小鼠脑干切片中，研究毒蕈碱对前包钦格复合体（preBötC）中形态学鉴定的甘氨酸能神经元的调节作用，preBötC是中枢吸气节律产生的关键区域。对甘氨酸能神经元进行生物胞素填充重建显示，它们中的大多数初级树突较少，轴突在其自身的树突野内分支。很少有甘氨酸能神经元有轴突侧支延伸至运动前区/运动区或伸向对侧preBötC，且有更多的初级树突和更紧密的树突树。在生理钾浓度下，自发活动的甘氨酸能神经元发放规则的动作电位，或较少以“爆发样”模式发放。毒蕈碱抑制大多数规则发放神经元的放电，通过M受体激活，同时通过M受体增强其余神经元的放电。有趣的是，在一小群甘氨酸能神经元中，毒蕈碱增强了节律性爆发。与其对甘氨酸能神经元兴奋性的异质性调节相反，毒蕈碱通常抑制甘氨酸能和非甘氨酸能preBötC神经元上的抑制性和兴奋性突触输入，对抑制性输入的影响更强。值得注意的是，兴奋性突触输入的突触前毒蕈碱衰减在甘氨酸能神经元中依赖于M受体，在非甘氨酸能神经元中依赖于M受体。对M受体敲除小鼠兴奋性突触电位的额外场电位记录表明，甘氨酸能和非甘氨酸能神经元对毒蕈碱对preBötC回路兴奋性活动的总体抑制作用贡献相等。总之，我们的数据表明，preBötC甘氨酸能神经元在形态上是异质的，与非甘氨酸能神经元相比，在突触传递特性和毒蕈碱调节方面存在差异。突触神经传递和动作电位发放的显性和细胞类型特异性毒蕈碱抑制可能导致高胆碱能状态下的中枢呼吸紊乱。
