Department of Neurobiology and Anatomy, Drexel University College of Medicine, Philadelphia, United States of America.
Cellular and Systems Neurobiology Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States of America.
PLoS Comput Biol. 2018 Apr 26;14(4):e1006148. doi: 10.1371/journal.pcbi.1006148. eCollection 2018 Apr.
The circuit organization within the mammalian brainstem respiratory network, specifically within and between the pre-Bötzinger (pre-BötC) and Bötzinger (BötC) complexes, and the roles of these circuits in respiratory pattern generation are continuously debated. We address these issues with a combination of optogenetic experiments and modeling studies. We used transgenic mice expressing channelrhodopsin-2 under the VGAT-promoter to investigate perturbations of respiratory circuit activity by site-specific photostimulation of inhibitory neurons within the pre-BötC or BötC. The stimulation effects were dependent on the intensity and phase of the photostimulation. Specifically: (1) Low intensity (≤ 1.0 mW) pulses delivered to the pre-BötC during inspiration did not terminate activity, whereas stronger stimulations (≥ 2.0 mW) terminated inspiration. (2) When the pre-BötC stimulation ended in or was applied during expiration, rebound activation of inspiration occurred after a fixed latency. (3) Relatively weak sustained stimulation (20 Hz, 0.5-2.0 mW) of pre-BötC inhibitory neurons increased respiratory frequency, while a further increase of stimulus intensity (> 3.0 mW) reduced frequency and finally (≥ 5.0 mW) terminated respiratory oscillations. (4) Single pulses (0.2-5.0 s) applied to the BötC inhibited rhythmic activity for the duration of the stimulation. (5) Sustained stimulation (20 Hz, 0.5-3.0 mW) of the BötC reduced respiratory frequency and finally led to apnea. We have revised our computational model of pre-BötC and BötC microcircuits by incorporating an additional population of post-inspiratory inhibitory neurons in the pre-BötC that interacts with other neurons in the network. This model was able to reproduce the above experimental findings as well as previously published results of optogenetic activation of pre-BötC or BötC neurons obtained by other laboratories. The proposed organization of pre-BötC and BötC circuits leads to testable predictions about their specific roles in respiratory pattern generation and provides important insights into key circuit interactions operating within brainstem respiratory networks.
哺乳动物脑干呼吸网络中的回路组织，特别是在 Pre-Bötzinger (pre-BötC) 和 Bötzinger (BötC) 复合体内部和之间，以及这些回路在呼吸模式产生中的作用，一直存在争议。我们通过光遗传学实验和建模研究来解决这些问题。我们使用表达通道视紫红质-2 的转基因小鼠，通过在 Pre-BötC 或 BötC 内的抑制性神经元的位置特异性光刺激来研究呼吸回路活动的干扰。刺激效果取决于光刺激的强度和相位。具体来说：(1) 在吸气时，传递到 Pre-BötC 的低强度（≤ 1.0 mW）脉冲不会终止活动，而更强的刺激（≥ 2.0 mW）则会终止吸气。(2) 当 Pre-BötC 刺激在呼气中结束或应用时，在固定潜伏期后会出现吸气的反弹激活。(3) 相对较弱的持续刺激（20 Hz，0.5-2.0 mW）可以增加呼吸频率，而进一步增加刺激强度（> 3.0 mW）会降低频率，最终（≥ 5.0 mW）终止呼吸振荡。(4) 施加到 BötC 的单个脉冲（0.2-5.0 s）会抑制节律性活动，持续时间与刺激时间相同。(5) 持续刺激（20 Hz，0.5-3.0 mW）BötC 会降低呼吸频率，最终导致呼吸暂停。我们通过在 Pre-BötC 中引入一个额外的吸气后抑制性神经元群体，对 Pre-BötC 和 BötC 微电路的计算模型进行了修订，该群体与网络中的其他神经元相互作用。该模型能够重现上述实验结果，以及其他实验室通过光遗传学激活 Pre-BötC 或 BötC 神经元获得的先前发表的结果。所提出的 Pre-BötC 和 BötC 电路的组织导致了对其在呼吸模式产生中的特定作用的可测试预测，并为脑干呼吸网络中关键回路相互作用提供了重要的见解。
