CIHR Group in Sensory-Motor Integration, Department of Biomedical and Molecular Sciences and Center for Neuroscience Studies, Queen's University, Kingston, ON K7L 3N6, Canada.
J Comp Neurol. 2013 Feb 15;521(3):638-56. doi: 10.1002/cne.23196.
The input-output properties of motoneurons are dynamically regulated. This regulation depends, in part, on the relative location of excitatory and inhibitory synapses, voltage-dependent and -independent channels, and neuromodulatory synapses on the dendritic tree. The goal of the present study was to quantify the number and distribution of synapses from two powerful neuromodulatory systems that originate from noradrenergic (NA) and serotonergic (5-HT) neurons. Here we show that the dendritic trees of motoneurons innervating a dorsal neck extensor muscle, splenius, in the adult cat are densely, but not uniformly innervated by both NA and 5-HT boutons. Identified splenius motoneurons were intracellularly stained with Neurobiotin. Using 3D reconstruction techniques we mapped the distributions of contacts formed by NA and 5-HT boutons on the reconstructed dendritic trees of these motoneurons. Splenius motoneurons received an average of 1,230 NA contacts (range = 647-1,507) and 1,582 5-HT contacts (range = 1,234-2,143). The densities of these contacts were 10 (NA) to 6 (5-HT)-fold higher on small compared to large-diameter dendrites. This relationship largely accounts for the bias of NA and 5-HT contacts on distal dendrites and is partially responsible for the higher density of NA contacts on dendrites located more than 200 μm dorsal to the soma. These results suggest that the neuromodulatory actions of NA and 5-HT are compartmentalized and regulate the input-output properties of motoneurons according to precisely arranged interactions with voltage-dependent and -independent channels that are primarily located on small-diameter dendrites.
运动神经元的输入-输出特性是动态调节的。这种调节部分依赖于兴奋性和抑制性突触、电压依赖性和非依赖性通道以及树突上的神经调质突触的相对位置。本研究的目的是量化源自去甲肾上腺素（NA）和 5-羟色胺（5-HT）神经元的两个强大的神经调质系统的突触数量和分布。在这里，我们展示了支配成年猫背颈伸肌（splenius）的运动神经元的树突被 NA 和 5-HT 末梢密集但不均匀地支配。用 Neurobiotin 对识别出的 splenius 运动神经元进行细胞内染色。使用 3D 重建技术，我们绘制了 NA 和 5-HT 末梢在这些运动神经元重建的树突上形成的接触分布。splenius 运动神经元平均接收 1230 个 NA 接触点（范围为 647-1507）和 1582 个 5-HT 接触点（范围为 1234-2143）。与大直径树突相比，这些接触点在小直径树突上的密度高 10（NA）到 6（5-HT）倍。这种关系在很大程度上解释了 NA 和 5-HT 接触点在远端树突上的偏向性，并且部分解释了位于距体细胞 200 μm 以上的树突上 NA 接触点密度更高的原因。这些结果表明，NA 和 5-HT 的神经调质作用是分区的，并根据主要位于小直径树突上的电压依赖性和非依赖性通道的精确排列相互作用来调节运动神经元的输入-输出特性。
