Departments of Medical Neuroscience, and Mathematics and Statistics, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada, and Molecular Neurobiology Laboratory, the Salk Institute for Biological Studies, La Jolla, California 92037.
J Neurosci. 2013 Nov 20;33(47):18553-65. doi: 10.1523/JNEUROSCI.2005-13.2013.
V3 interneurons (INs) are a major group of excitatory commissural interneurons in the spinal cord, and they are essential for producing a stable and robust locomotor rhythm. V3 INs are generated from the ventral-most progenitor domain, p3, but migrate dorsally and laterally during postmitotic development. At birth, they are located in distinctive clusters in the ventral horn and deep dorsal horn. To assess the heterogeneity of this genetically identified group of spinal INs, we combined patch-clamp recording and anatomical tracing with cluster analysis. We examined electrophysiological and morphological properties of mature V3 INs identified by their expression of tdTomato fluorescent proteins in Sim1(Cre/+); Rosa(floxstop26TdTom) mice. We identified two V3 subpopulations with distinct intrinsic properties and spatial distribution patterns. Ventral V3 INs, primarily located in lamina VIII, possess a few branching processes and were capable of generating rapid tonic firing spikes. By contrast, dorsal V3 INs exhibited a more complex morphology and relatively slow average spike frequency with strong adaptation, and they also displayed large sag voltages and post-inhibitory rebound potentials. Our data suggested that hyperpolarization-activated cation channel currents and T-type calcium channel currents may account for some of the membrane properties of V3 INs. Finally, we observed that ventral and dorsal V3 INs were active in different ways during running and swimming, indicating that ventral V3 INs may act as premotor neurons and dorsal V3 INs as relay neurons mediating sensory inputs. Together, we detected two physiologically and topographically distinct subgroups of V3 INs, each likely playing different roles in locomotor activities.
V3 中间神经元（INs）是脊髓中兴奋性连合中间神经元的主要群体，对于产生稳定而有力的运动节律至关重要。V3 INs 由最腹侧的祖细胞区 p3 产生，但在出生后有丝分裂后发育过程中向背侧和外侧迁移。出生时，它们位于腹角和深部背角的独特簇中。为了评估这群遗传鉴定的脊髓 INs 的异质性，我们将膜片钳记录和解剖追踪与聚类分析相结合。我们检查了 Sim1(Cre/+); Rosa(floxstop26TdTom) 小鼠中表达 tdTomato 荧光蛋白的成熟 V3 INs 的电生理和形态特性。我们鉴定了两个具有不同内在特性和空间分布模式的 V3 亚群。腹侧 V3 INs 主要位于 VIII 层，具有几个分支过程，能够产生快速的紧张性放电尖峰。相比之下，背侧 V3 INs 表现出更复杂的形态和相对较慢的平均尖峰频率，具有强烈的适应性，并且它们还显示出较大的 sag 电压和抑制后反弹电位。我们的数据表明，超极化激活阳离子通道电流和 T 型钙通道电流可能解释了 V3 INs 的一些膜特性。最后，我们观察到腹侧和背侧 V3 INs 在跑步和游泳时以不同的方式活跃，表明腹侧 V3 INs 可能作为运动前神经元，而背侧 V3 INs 作为介导感觉输入的中继神经元发挥作用。总之，我们检测到两种生理和地形上明显不同的 V3 INs 亚群，每种亚群在运动活动中可能发挥不同的作用。
