Institute of Neuroscience and Psychology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK.
Department of Morphological Brain Science, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan.
Neuroscience. 2017 Nov 5;363:120-133. doi: 10.1016/j.neuroscience.2017.08.044. Epub 2017 Aug 30.
Around a quarter of neurons in laminae I-II of the dorsal horn are inhibitory interneurons. These play an important role in modulating somatosensory information, including that perceived as pain or itch. Previous studies in rat identified four largely non-overlapping neurochemical populations among these cells, defined by expression of galanin, neuropeptide Y (NPY), neuronal nitric oxide synthase (nNOS) or parvalbumin. The galanin cells were subsequently shown to coexpress dynorphin. Several recent studies have used genetically modified mice to investigate the function of different interneuron populations, and it is therefore important to determine whether the same pattern applies in mouse, and to estimate the relative sizes of these populations. We show that the neurochemical organization of inhibitory interneurons in mouse superficial dorsal horn is similar to that in the rat, although a larger proportion of these neurons (33%) express NPY. Between them, these four populations account for ∼75% of inhibitory cells in laminae I-II. Since ∼25% of inhibitory interneurons in this region belong to a novel calretinin-expressing type, our results suggest that virtually all inhibitory interneurons in superficial dorsal horn can be assigned to one of these five neurochemical populations. Although our main focus was inhibitory neurons, we also identified a population of excitatory dynorphin-expressing cells in laminae I-II that are largely restricted to the medial part of the mid-lumbar dorsal horn, corresponding to glabrous skin territory. These findings are important for interpretation of studies using molecular-genetic techniques to manipulate the functions of interneuron populations to investigate their roles in somatosensory processing.
背角浅层 I-II 层中约四分之一的神经元为抑制性中间神经元。这些神经元在调节躯体感觉信息（包括被感知为疼痛或瘙痒的信息）方面发挥着重要作用。先前在大鼠中的研究确定了这些细胞中存在四种基本不重叠的神经化学群体，它们的特征是甘丙肽、神经肽 Y（NPY）、神经元型一氧化氮合酶（nNOS）或钙结合蛋白 Parvalbumin 的表达。随后的研究表明，甘丙肽细胞共同表达强啡肽。最近的几项研究使用基因修饰小鼠来研究不同中间神经元群体的功能，因此，确定这种模式是否适用于小鼠并估计这些群体的相对大小非常重要。我们的研究表明，小鼠背角浅层抑制性中间神经元的神经化学组织与大鼠相似，尽管这些神经元中更大比例（33%）表达 NPY。这四种群体共同构成了 I-II 层中约 75%的抑制性细胞。由于该区域中约 25%的抑制性中间神经元属于新型钙结合蛋白 Calretinin 表达类型，因此我们的结果表明，浅层背角中的几乎所有抑制性中间神经元都可以归属于这五个神经化学群体之一。尽管我们的主要关注点是抑制性神经元，但我们还在 I-II 层中鉴定出了一群表达强啡肽的兴奋性神经元，这些神经元主要局限于中腰背部背角的内侧部分，对应于无毛皮肤区域。这些发现对于解释使用分子遗传技术来操纵中间神经元群体的功能以研究它们在躯体感觉处理中的作用的研究非常重要。
