Blitz Dawn M
Department of Biology and Center for Neuroscience, Miami University, Oxford, OH, United States.
Front Neurosci. 2023 Mar 17;17:1154769. doi: 10.3389/fnins.2023.1154769. eCollection 2023.
Rhythmic behaviors (e.g., walking, breathing, and chewing) are produced by central pattern generator (CPG) circuits. These circuits are highly dynamic due to a multitude of input they receive from hormones, sensory neurons, and modulatory projection neurons. Such inputs not only turn CPG circuits on and off, but they adjust their synaptic and cellular properties to select behaviorally relevant outputs that last from seconds to hours. Similar to the contributions of fully identified connectomes to establishing general principles of circuit function and flexibility, identified modulatory neurons have enabled key insights into neural circuit modulation. For instance, while bath-applying neuromodulators continues to be an important approach to studying neural circuit modulation, this approach does not always mimic the neural circuit response to neuronal release of the same modulator. There is additional complexity in the actions of neuronally-released modulators due to: (1) the prevalence of co-transmitters, (2) local- and long-distance feedback regulating the timing of (co-)release, and (3) differential regulation of co-transmitter release. Identifying the physiological stimuli (e.g., identified sensory neurons) that activate modulatory projection neurons has demonstrated multiple "modulatory codes" for selecting particular circuit outputs. In some cases, population coding occurs, and in others circuit output is determined by the firing pattern and rate of the modulatory projection neurons. The ability to perform electrophysiological recordings and manipulations of small populations of identified neurons at multiple levels of rhythmic motor systems remains an important approach for determining the cellular and synaptic mechanisms underlying the rapid adaptability of rhythmic neural circuits.
节律性行为（如行走、呼吸和咀嚼）由中枢模式发生器（CPG）电路产生。这些电路高度动态，因为它们从激素、感觉神经元和调制投射神经元接收大量输入。此类输入不仅开启和关闭CPG电路，还会调整其突触和细胞特性，以选择持续数秒至数小时的行为相关输出。与完全确定的连接体对建立电路功能和灵活性的一般原则的贡献类似，已确定的调制神经元使人们对神经电路调制有了关键的认识。例如，虽然浴用神经调节剂仍然是研究神经电路调制的重要方法，但这种方法并不总是模拟神经电路对相同调节剂神经元释放的反应。神经元释放的调节剂的作用还存在额外的复杂性，原因如下：（1）共递质的普遍存在；（2）调节（共）释放时间的局部和长距离反馈；（3）共递质释放的差异调节。识别激活调制投射神经元的生理刺激（如已确定的感觉神经元）已证明存在多种用于选择特定电路输出的“调制代码”。在某些情况下，会发生群体编码，而在其他情况下，电路输出由调制投射神经元的放电模式和速率决定。在节律性运动系统的多个层面上对少量已确定神经元进行电生理记录和操作的能力，仍然是确定节律性神经电路快速适应性背后的细胞和突触机制的重要方法。
