Li W-C, Soffe S R, Roberts Alan
School of Biological Sciences, University of Bristol, Bristol, BS8 1UG, United Kingdom.
J Neurosci. 2002 Dec 15;22(24):10924-34. doi: 10.1523/JNEUROSCI.22-24-10924.2002.
During locomotion, reflex responses to sensory stimulation are usually modulated and may even be reversed. This is thought to be the result of phased inhibition, but the neurons responsible are usually not known. When the hatchling Xenopus tadpole swims, responses to cutaneous stimulation are modulated. This occurs because sensory pathway interneurons receive rhythmic glycinergic inhibition broadly in phase with the motor discharge on the same side of the trunk. We now describe a new whole-cell recording preparation of the Xenopus tadpole CNS. This has been used with neurobiotin injection to define the passive and firing properties of spinal ascending interneurons and their detailed anatomy. Paired recordings show that they make direct, glycinergic synapses onto spinal sensory pathway interneurons, and the site of contact can be seen anatomically. During swimming, ascending interneurons fire rhythmically. Analysis shows that their firing is more variable and not as reliable as other interneurons, but the temporal pattern of their impulse activity is suitable to produce the main peak of gating inhibition in sensory pathway interneurons. Ascending interneurons are not excited at short latency after skin stimulation but are strongly active after repetitive skin stimulation, which evokes vigorous and slower struggling movements. We conclude that ascending interneurons are a major class of modulatory neurons producing inhibitory gating of cutaneous sensory pathways during swimming and struggling.
在运动过程中，对感觉刺激的反射反应通常会受到调节，甚至可能会反转。这被认为是阶段性抑制的结果，但通常不清楚负责的神经元。当非洲爪蟾幼体蝌蚪游泳时，对皮肤刺激的反应会受到调节。这是因为感觉通路中间神经元在躯干同一侧与运动放电大致同步地接受节律性甘氨酸能抑制。我们现在描述一种新的非洲爪蟾蝌蚪中枢神经系统的全细胞记录制备方法。它已与神经生物素注射一起用于确定脊髓上行中间神经元的被动和放电特性及其详细解剖结构。配对记录显示，它们在脊髓感觉通路中间神经元上形成直接的甘氨酸能突触，并且接触部位在解剖学上可见。在游泳过程中，上行中间神经元有节律地放电。分析表明，它们的放电比其他中间神经元更具变异性且不太可靠，但它们冲动活动的时间模式适合在感觉通路中间神经元中产生门控抑制的主要峰值。皮肤刺激后短潜伏期内，上行中间神经元不会被兴奋，但在重复性皮肤刺激后会强烈激活，重复性皮肤刺激会引发剧烈且较慢的挣扎动作。我们得出结论，上行中间神经元是一类主要的调节性神经元，在游泳和挣扎过程中对皮肤感觉通路产生抑制性门控作用。
