White Rachel S, Spencer Robert M, Nusbaum Michael P, Blitz Dawn M
Department of Neuroscience, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania.
Department of Biology, Miami University, Oxford, Ohio; and.
J Neurophysiol. 2017 Nov 1;118(5):2806-2818. doi: 10.1152/jn.00420.2017. Epub 2017 Aug 16.
Sensory feedback influences motor circuits and/or their projection neuron inputs to adjust ongoing motor activity, but its efficacy varies. Currently, less is known about regulation of sensory feedback onto projection neurons that control downstream motor circuits than about sensory regulation of the motor circuit neurons themselves. In this study, we tested whether sensory feedback onto projection neurons is sensitive only to activation of a motor system, or also to the modulatory state underlying that activation, using the crab stomatogastric nervous system. We examined how proprioceptor neurons (gastropyloric receptors, GPRs) influence the gastric mill (chewing) circuit neurons and the projection neurons (MCN1, CPN2) that drive the gastric mill rhythm. During gastric mill rhythms triggered by the mechanosensory ventral cardiac neurons (VCNs), GPR was shown previously to influence gastric mill circuit neurons, but its excitation of MCN1/CPN2 was absent. In this study, we tested whether GPR effects on MCN1/CPN2 are also absent during gastric mill rhythms triggered by the peptidergic postoesophageal commissure (POC) neurons. The VCN and POC pathways both trigger lasting MCN1/CPN2 activation, but their distinct influence on circuit feedback to these neurons produces different gastric mill motor patterns. We show that GPR excites MCN1 and CPN2 during the POC-gastric mill rhythm, altering their firing rates and activity patterns. This action changes both phases of the POC-gastric mill rhythm, whereas GPR only alters one phase of the VCN-gastric mill rhythm. Thus sensory feedback to projection neurons can be gated as a function of the modulatory state of an active motor system, not simply switched on/off with the onset of motor activity. Sensory feedback influences motor systems (i.e., motor circuits and their projection neuron inputs). However, whether regulation of sensory feedback to these projection neurons is consistent across different versions of the same motor pattern driven by the same motor system was not known. We found that gating of sensory feedback to projection neurons is determined by the modulatory state of the motor system, and not simply by whether the system is active or inactive.
感觉反馈会影响运动回路和/或其投射神经元输入，以调整正在进行的运动活动，但其效果各不相同。目前，相较于对运动回路神经元本身的感觉调节，我们对控制下游运动回路的投射神经元上的感觉反馈调节了解较少。在本研究中，我们利用蟹的口胃神经系统，测试了投射神经元上的感觉反馈是否仅对运动系统的激活敏感，还是也对该激活背后的调节状态敏感。我们研究了本体感受器神经元（胃幽门感受器，GPRs）如何影响胃磨（咀嚼）回路神经元以及驱动胃磨节律的投射神经元（MCN1、CPN2）。在由机械感觉性腹侧心神经元（VCNs）触发的胃磨节律期间，先前已表明GPR会影响胃磨回路神经元，但它对MCN1/CPN2没有兴奋作用。在本研究中，我们测试了在由肽能性食管后连合（POC）神经元触发的胃磨节律期间，GPR对MCN1/CPN2的作用是否也不存在。VCN和POC通路都会触发MCN1/CPN2的持续激活，但它们对这些神经元的回路反馈有不同影响，从而产生不同的胃磨运动模式。我们发现，在POC - 胃磨节律期间，GPR会兴奋MCN1和CPN2，改变它们的放电频率和活动模式。这一作用改变了POC - 胃磨节律的两个阶段，而GPR仅改变VCN - 胃磨节律的一个阶段。因此，对投射神经元的感觉反馈可以根据活跃运动系统的调节状态进行门控，而不仅仅是随着运动活动的开始而开启/关闭。感觉反馈会影响运动系统（即运动回路及其投射神经元输入）。然而，对于由同一运动系统驱动的相同运动模式的不同版本，对这些投射神经元的感觉反馈调节是否一致尚不清楚。我们发现，对投射神经元的感觉反馈门控是由运动系统的调节状态决定的，而不仅仅取决于该系统是否活跃。
