Le Ray D, Clarac F, Cattaert D
Laboratoire de Neurobiologie et Mouvements, Centre National de la Recherche Scientifique, Marseille Cedex 20, France.
J Neurophysiol. 1997 Dec;78(6):3144-53. doi: 10.1152/jn.1997.78.6.3144.
The in vitro preparation of the fifth thoracic ganglion of the crayfish was used to analyze the connections supporting the monosynaptic reflex responses recorded from the depressor motor neurons (Dep MNs). Dep MNs are directly connected by the release-sensitive afferents from a proprioceptor, the coxo-basipodite chordotonal organ (CBCO), which is released by upward movements of the leg. Sine-wave movements, applied to the CBCO strand from the most released position, allowed us to stimulate the greatest part of release-sensitive CBCO fibers. Systematic intracellular recordings from all Dep MNs performed in high divalent cation saline allowed us to determine the connections between CBCO afferents and their postsynaptic Dep MNs: it highlighted the sequential activation of the different Dep MNs involved in the monosynaptic reflex. The convergence of different sensory afferents onto a given Dep MN, and the divergence of a given sensory afferent onto several Dep MNs illustrates the complexity of the sensory-motor reflex loops involved in the control of locomotion and posture. Electrophysiological experiments and simulations were performed to analyze the mechanisms by which Dep MNs integrate the large amount of sensory input that they receive. Paired intracellular recording experiments demonstrated that postsynaptic response shapes characteristic of both phasic and phaso-tonic afferents could be induced by varying the presynaptic firing frequency, whatever the postsynaptic Dep MN. Compartment model simulations were used to analyze the role of the sensory-motor synapse characteristics in the summation properties of postsynaptic MN. They demonstrated the importance of the postsynaptic compartment geometry, because large postsynaptic compartments allowed to generate greater excitatory postsynaptic potential (EPSP) summations than small ones. The results presented show that velocity information is the most effective to elicit large compound EPSPs in MNs. We therefore suggest that the negative feedback reflex is mainly based on the detection of leg movements.
利用小龙虾第五胸神经节的体外制备物，分析支持从降压运动神经元（Dep MNs）记录到的单突触反射反应的连接。Dep MNs通过来自本体感受器——基节-底节弦音器（CBCO）的释放敏感传入纤维直接相连，腿部向上运动时会释放该感受器。从最释放位置向CBCO束施加正弦波运动，使我们能够刺激大部分释放敏感的CBCO纤维。在高双价阳离子盐溶液中对所有Dep MNs进行系统的细胞内记录，使我们能够确定CBCO传入纤维与其突触后Dep MNs之间的连接：它突出了参与单突触反射的不同Dep MNs的顺序激活。不同感觉传入纤维汇聚到给定的Dep MN上，以及给定的感觉传入纤维发散到多个Dep MN上，说明了参与运动和姿势控制的感觉运动反射回路的复杂性。进行了电生理实验和模拟，以分析Dep MNs整合它们所接收的大量感觉输入的机制。配对细胞内记录实验表明，无论突触后Dep MN如何，通过改变突触前放电频率，可以诱导出相位性和相位-紧张性传入纤维特有的突触后反应形状。利用房室模型模拟来分析感觉运动突触特性在突触后运动神经元总和特性中的作用。它们证明了突触后房室几何形状的重要性，因为大的突触后房室比小的房室能产生更大的兴奋性突触后电位（EPSP）总和。所呈现的结果表明，速度信息最有效地在运动神经元中引发大的复合EPSP。因此，我们认为负反馈反射主要基于对腿部运动的检测。
