Spinal Cord Group, Institute of Neuroscience and Psychology, College of Medicine, Veterinary Medicine and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK.
J Physiol. 2010 Nov 1;588(Pt 21):4217-33. doi: 10.1113/jphysiol.2010.192211. Epub 2010 Sep 13.
The intermediate zone of the spinal grey matter contains premotor interneurons mediating reflex actions of group I and II muscle afferents. However, limited information is available on how activity of inhibitory versus excitatory interneurons in this population are modulated and how they contribute to motor networks. There were three aims of this study: (1) to characterize excitatory axonal contacts on interneurons; (2) to determine if contact patterns on excitatory and inhibitory interneurons are different; (3) to determine if there are differences in presynaptic inhibitory control of excitatory and inhibitory interneurons. We used intracellular labelling of electrophysiologically identified cells along with immunochemistry to characterise contacts formed by axons that contain vesicular glutamate transporters (VGLUT1 and VGLUT2) and contacts formed by VGLUT1 terminals which in turn were contacted by GABAergic terminals on cells that were characterised according to their transmitter phenotype. All 17 cells investigated were associated with numerous VGLUT1 contacts originating from primary afferents, and similar contact densities were found on excitatory and inhibitory cells, but VGLUT2-immunoreactive terminals originating from intraspinal neurons were less frequent, or were practically absent, especially on excitatory cells. Similar numbers of VGLUT1 contacts with associated GABAergic terminals were found on excitatory and inhibitory cells indicating a similar extent of presynaptic GABAergic control. However, scarce VGLUT2 terminals on intermediate zone excitatory premotor interneurons with input from muscle afferents suggest that they are not significantly excited by other spinal neurons but are under direct excitatory control of supraspinal neurons and, principally inhibitory, control of spinal neurons.
脊髓灰质的中间区包含介导 I 类和 II 类肌传入反射活动的运动前中间神经元。然而，关于该群体中抑制性和兴奋性中间神经元的活动如何被调节以及它们如何对运动网络做出贡献，信息有限。本研究有三个目的：（1）描述中间神经元上的兴奋性轴突接触；（2）确定兴奋性和抑制性中间神经元上的接触模式是否不同；（3）确定兴奋性和抑制性中间神经元的突触前抑制控制是否存在差异。我们使用电生理鉴定的细胞的细胞内标记以及免疫化学来描述包含囊泡谷氨酸转运体（VGLUT1 和 VGLUT2）的轴突形成的接触，以及由 GABA 能末梢形成的接触，这些末梢反过来又与根据其递质表型进行了特征化的细胞上的 VGLUT1 末梢接触。研究的 17 个细胞都与来自初级传入的大量 VGLUT1 接触有关，兴奋性和抑制性细胞上的接触密度相似，但来自脊髓内神经元的 VGLUT2-免疫反应性末梢较少，或者实际上不存在，尤其是在兴奋性细胞上。在兴奋性和抑制性细胞上发现了数量相似的具有相关 GABA 能末梢的 VGLUT1 接触，表明存在相似程度的突触前 GABA 能控制。然而，来自肌肉传入的中间区兴奋性运动前中间神经元上的 VGLUT2 末梢稀少，这表明它们不是由其他脊髓神经元显著兴奋，而是受脊髓上神经元的直接兴奋控制，主要是由脊髓神经元的抑制控制。
