Institute of Neuroscience and Psychology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK.
Department of Oral Anatomy and Neurobiology, Graduate School of Dentistry, Osaka University, 1-8 Yamada-Oka, Suita, Osaka 565-0871, Japan.
Neuroscience. 2019 Feb 1;398:171-181. doi: 10.1016/j.neuroscience.2018.12.009. Epub 2018 Dec 13.
Around 75% of neurons in laminae I-II of the mouse dorsal horn are excitatory interneurons, and these are required for normal pain perception. We have shown that four largely non-overlapping excitatory interneuron populations can be defined by expression of the neuropeptides neurotensin, neurokinin B (NKB), gastrin-releasing peptide (GRP) and substance P. In addition, we recently identified a population of excitatory interneurons in glabrous skin territory that express dynorphin. The calcium-binding protein calretinin is present in many excitatory neurons in this region, but we know little about its relation to these neuropeptide markers. Here we show that calretinin is differentially expressed, being present in the majority of substance P-, GRP- and NKB-expressing cells, but not in the neurotensin or dynorphin cells. Calretinin-positive cells have been implicated in detection of noxious mechanical stimuli, but are not required for tactile allodynia after neuropathic pain. Our findings are therefore consistent with the suggestion that neuropathic allodynia involves the neurotensin and/or dynorphin excitatory interneuron populations. Around a quarter of inhibitory interneurons in lamina I-II contain calretinin, and recent transcriptomic studies suggest that these co-express substance P. We confirm this, by showing that inhibitory Cre-expressing cells in a Tac1 knock-in mouse are calretinin-immunoreactive. Interestingly, there is evidence that these cells express low levels of peptidylglycine alpha-amidating monooxygenase, an enzyme required for maturation of neuropeptides. This may explain our previous finding that although the substance P precursor preprotachykinin A can be detected in some inhibitory interneurons, very few inhibitory axonal boutons are immunoreactive for substance P.
大约 75%的小鼠背角 I-II 层神经元为兴奋性中间神经元，这些神经元对于正常的疼痛感知是必需的。我们已经表明，可以通过神经降压素、神经激肽 B (NKB)、胃泌素释放肽 (GRP) 和 P 物质的表达来定义四个基本不重叠的兴奋性中间神经元群体。此外，我们最近在无毛皮肤区域鉴定出一群表达强啡肽的兴奋性中间神经元。钙结合蛋白 calretinin 存在于该区域的许多兴奋性神经元中，但我们对其与这些神经肽标记物的关系知之甚少。在这里，我们表明 calretinin 表达不同，存在于大多数 P 物质、GRP 和 NKB 表达细胞中，但不存在于神经降压素或强啡肽细胞中。 calretinin 阳性细胞已被牵连到检测有害机械刺激，但在神经病理性疼痛后的触觉过敏中并非必需。因此，我们的发现与神经病理性痛涉及神经降压素和/或强啡肽兴奋性中间神经元群体的观点一致。 I-II 层约四分之一的抑制性中间神经元含有 calretinin，最近的转录组研究表明这些细胞共表达 P 物质。我们通过显示 Tac1 敲入小鼠中的抑制性 Cre 表达细胞为 calretinin 免疫反应性来证实这一点。有趣的是，有证据表明这些细胞表达低水平的肽基甘氨酸 α-酰胺化单加氧酶，这是神经肽成熟所必需的酶。这可以解释我们之前的发现，即尽管 P 物质前体前强啡肽 A 可以在一些抑制性中间神经元中检测到，但很少有抑制性轴突末梢对 P 物质呈免疫反应性。
