Soffe S R, Zhao F Y, Roberts A
School of Biological Sciences, University of Bristol, Woodland Road, Bristol, BS8 1UG, UK.
Eur J Neurosci. 2001 Feb;13(3):617-27. doi: 10.1046/j.1460-9568.2001.01419.x.
The basis for longitudinal coordination among spinal neurons during locomotion is still poorly understood. We have now examined the functional projection distances for the longitudinal axons of reciprocal inhibitory 'commissural interneurons' in the spinal cord of young Xenopus tadpoles. In quiescent animals, glycinergic inhibitory postsynaptic potentials (IPSPs) were evoked in ventral spinal neurons by stimulating small rostral and caudal groups of commissural interneuron somata at different distances on the opposite side of the hindbrain and spinal cord. Unitary IPSPs, produced by single synaptic contacts, could be distinguished from background noise. Local cord stimulation at different distances revealed maximum functional projection distances up to approximately 0.5 mm for both descending and ascending axons, but with the probability of recording connections falling steeply over this distance. These maximum longitudinal projection distances are smaller than predicted by axonal anatomy (approximately 1.2 mm). We then measured functional projection distances during swimming by examining the synaptic output of a surgically isolated group of rostral commissural interneurons, mapping the occurrence of the mid-cycle, reciprocal IPSPs they produced in more caudal neurons. IPSPs occurred with high probability up to 0.9 mm away, nearly twice the projection distance found in quiescent tadpoles. These results show that synaptic contacts from commissural interneurons could influence longitudinal coupling during swimming at distances of up to 0.9 mm (approximately 4-5 myotome segments or approximately 25% of the spinal cord). They provide direct evidence for functional projection distances of a characterized class of interneurons belonging to a spinal locomotor pattern generator.
运动过程中脊髓神经元之间纵向协调的基础仍知之甚少。我们现在研究了非洲爪蟾幼体脊髓中相互抑制性“连合中间神经元”纵向轴突的功能投射距离。在静止的动物中，通过刺激后脑和脊髓对侧不同距离处的小群连合中间神经元胞体，在脊髓腹侧神经元中诱发甘氨酸能抑制性突触后电位（IPSPs）。由单个突触接触产生的单一IPSPs可以与背景噪声区分开来。在不同距离进行局部脊髓刺激显示，下行和上行轴突的最大功能投射距离均可达约0.5毫米，但在此距离上记录到连接的概率急剧下降。这些最大纵向投射距离比轴突解剖学预测的要小（约1.2毫米）。然后，我们通过检查一组手术分离的吻侧连合中间神经元的突触输出，测量了游泳过程中的功能投射距离，绘制了它们在更尾侧神经元中产生的周期中期相互IPSPs的出现情况。IPSPs在距离达0.9毫米处出现的概率很高，几乎是静止蝌蚪中发现的投射距离的两倍。这些结果表明，连合中间神经元的突触接触在游泳过程中可在长达0.9毫米（约4 - 5个肌节段或约脊髓的25%）的距离上影响纵向耦合。它们为属于脊髓运动模式发生器的一类特定中间神经元的功能投射距离提供了直接证据。
