Sillar K T, Roberts A
Department of Zoology, University of Bristol, UK.
Nature. 1988 Jan 21;331(6153):262-5. doi: 10.1038/331262a0.
The response of the foot to touch during walking depends on whether it is in the air or on the ground. In most animals, reflex responses to external stimuli are similarly adapted to their timing in the locomotor cycle, but there is only fragmentary information about the neural mechanisms involved. In arthropods, reflex modulation can occur in the sensory receptors themselves and in neurons that discharge during locomotion. By recording with dye-filled microelectrodes from neurons in the spinal cord of frog embryos, we describe reflex modulation at the level of sensory interneurons. Sensory inputs from skin receptors excite a specific class of spinal sensory interneuron whose activity leads to reflex bending of the body away from the stimulus. During swimming, these inputs are gated by rhythmic postsynaptic inhibition, so that sensory drive reaches motor neurons only at phases in the locomotor cycle when the resulting contraction would likewise turn the embryo away from the stimulated side. Such gating of sensory pathways could be a general feature of all locomotor systems where responses to sensory stimuli need to be adapted to the phase of locomotion.
行走过程中足部对触碰的反应取决于其是在空中还是在地面上。在大多数动物中，对外部刺激的反射反应同样会根据其在运动周期中的时间进行调整，但关于其中涉及的神经机制只有零散的信息。在节肢动物中，反射调制可发生在感觉受体本身以及运动过程中放电的神经元中。通过用染料填充的微电极记录青蛙胚胎脊髓中的神经元，我们描述了感觉中间神经元水平的反射调制。来自皮肤感受器的感觉输入会激发一类特定的脊髓感觉中间神经元，其活动会导致身体向远离刺激的方向反射性弯曲。在游泳过程中，这些输入通过有节奏的突触后抑制进行门控，这样感觉驱动仅在运动周期的特定阶段到达运动神经元，此时产生的收缩同样会使胚胎转向远离受刺激的一侧。这种感觉通路的门控可能是所有运动系统的一个普遍特征，在这些系统中，对感觉刺激的反应需要根据运动阶段进行调整。
