Department of Physiology and Center for Neuroscience, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin 53706, USA.
J Neurosci. 2011 Mar 30;31(13):4821-33. doi: 10.1523/JNEUROSCI.4764-10.2011.
Commissural inhibitory interneurons (INs) are integral components of the locomotor circuitry that coordinate left-right motor activity during movements. We have shown that GABA-mediated synaptic transmission plays a key role in generating alternating locomotor-like activity in the mouse spinal cord (Hinckley et al., 2005a). The primary objective of our study was to determine whether properties of lamina VIII (LVIII) GABAergic INs in the spinal cord of GAD67::GFP transgenic mice fit the classification of rhythm-coordinating neurons in the locomotor circuitry. The relatively large green fluorescent protein-expressing (GFP(+)) INs had comparable morphological and electrophysiological properties, suggesting that they comprised a homogenous neuronal population. They displayed multipolar and complex dendritic arbors in ipsilateral LVII-LVIII, and their axonal projections crossed the ventral commissure and branched into contralateral ventral, medial, and dorsal laminae. Putative synaptic contacts evident as bouton-like varicosities were detected in close apposition to lateral motoneurons, Renshaw cells, other GFP(+) INs, and unidentified neurons. Exposure to a rhythmogenic mixture triggered locomotor-like rhythmic firing in the majority of LVIII GFP(+) INs. Their induced oscillatory activity was out-of-phase with bursts of contralateral motoneurons and in-phase with bouts of ipsilateral motor activity. Membrane voltage oscillations were elicited by rhythmic increases in excitatory synaptic drive and might have been augmented by three types of voltage-activated cationic currents known to increase neuronal excitability. Based on their axonal projections and activity pattern, we propose that this population of GABAergic INs forms a class of local commissural inhibitory interneurons that are integral component of the locomotor circuitry.
联络性抑制性中间神经元（INs）是协调运动过程中左右运动活动的运动回路的组成部分。我们已经表明，GABA 介导的突触传递在产生小鼠脊髓中的交替运动样活动中起着关键作用（Hinckley 等人，2005a）。我们研究的主要目的是确定 GAD67::GFP 转基因小鼠脊髓中VIII 层（LVIII）GABA 能 INs 的特性是否符合运动回路中协调神经元的分类。相对较大的绿色荧光蛋白表达（GFP(+））INs 具有可比的形态和电生理特性，表明它们构成了同质神经元群体。它们在同侧 LVII-LVIII 中显示出多极和复杂的树突状树突，其轴突投射穿过腹侧联合，并分支到对侧腹侧、内侧和背侧层。作为突状小泡的假定突触接触被检测到与外侧运动神经元、Renshaw 细胞、其他 GFP(+)INs 和未识别神经元紧密毗邻。暴露于节律生成混合物中会引发大多数 LVIII GFP(+)INs 的运动样节律性放电。它们诱导的振荡活动与对侧运动神经元的爆发不同步，与同侧运动活动的爆发同步。膜电压振荡是由兴奋性突触驱动的节律性增加引起的，并且可能会被三种已知增加神经元兴奋性的电压激活阳离子电流增强。基于它们的轴突投射和活动模式，我们提出该群 GABA 能 INs 形成了一类局部联络性抑制性中间神经元，是运动回路的组成部分。
