García-Magro Nuria, Martin Yasmina B, Palomino-Antolin Alejandra, Egea Javier, Negredo Pilar, Avendaño Carlos
Department of Anatomy, Histology and Neuroscience, Medical School, Autonomous University of Madrid, Madrid, Spain.
Ph.D. Programme in Neuroscience, Doctoral School, Autonomous University of Madrid, Madrid, Spain.
Front Neuroanat. 2020 Jan 22;13:103. doi: 10.3389/fnana.2019.00103. eCollection 2019.
Microglia (MG) are the first cells to react to the abnormal incoming signals that follow an injury of sensory nerves and play a critical role in the development and maintenance of neuropathic pain, a common sequel of nerve injuries. Here we present population data on cell number, soma size, and length of processes of MG in the caudal division of the spinal trigeminal nucleus (Sp5C) in control mice and at the peak of microgliosis (7 days) following unilateral transection of the infraorbital nerve (IoN). The study is performed combining several bias- and assumption-free imaging and stereological approaches with different immunolabeling procedures, with the objective of tackling some hard problems that often hinder proper execution of MG morphometric studies. Our approach may easily be applied to low-density MG populations, but also works, with limited biases, in territories where MG cell bodies and processes form dense meshworks. In controls, and contralaterally to the deafferented side, MG cell body size and shape and branching pattern matched well the descriptions of "resting" or "surveillant" MG described elsewhere, with only moderate intersubject variability. On the superficial laminae of the deafferented side, however, MG displayed on average larger somata and remarkable diversity in shape. The number of cells and the length of MG processes per mm increased 5 and 2.5 times, respectively, indicating a net 50% decrease in the mean length of processes per cell. By using specific immunolabeling and cell sorting of vascular macrophages, we found only a negligible fraction of these cells in Sp5C, with no differences between controls and deafferented animals, suggesting that blood-borne monocytes play at most a very limited role in the microgliosis occurring following sensory nerve deafferentation. In sum, here we present reliable morphometric data on MG in control and deafferented trigeminal nuclei using efficient methods that we propose may equally be applied to any morphometric population analysis of these cells under different physiological or pathological conditions.
小胶质细胞（MG）是对感觉神经损伤后异常传入信号产生反应的首批细胞，在神经性疼痛（神经损伤的常见后遗症）的发生和维持中起关键作用。在此，我们展示了对照小鼠以及眶下神经（IoN）单侧横断后小胶质细胞增生高峰期（7天）时，脊髓三叉神经核尾侧部（Sp5C）中小胶质细胞的细胞数量、胞体大小和突起长度的群体数据。本研究结合了多种无偏差和无假设的成像及体视学方法与不同的免疫标记程序，旨在解决一些常常阻碍小胶质细胞形态计量学研究正确开展的难题。我们的方法可轻松应用于低密度小胶质细胞群体，而且在小胶质细胞胞体和突起形成密集网络的区域也能以有限的偏差发挥作用。在对照组以及与去传入侧相对的对侧，小胶质细胞的胞体大小、形状和分支模式与其他地方描述的“静息”或“监视性”小胶质细胞非常吻合，个体间差异仅为中等程度。然而，在去传入侧的浅层层，小胶质细胞平均显示出更大的胞体和显著的形状多样性。每毫米的细胞数量和小胶质细胞突起长度分别增加了5倍和2.5倍，表明每个细胞的突起平均长度净减少了50%。通过使用血管巨噬细胞的特异性免疫标记和细胞分选，我们在Sp5C中仅发现了可忽略不计的这些细胞比例，对照组和去传入动物之间没有差异，这表明血源性单核细胞在感觉神经去传入后发生的小胶质细胞增生中至多发挥非常有限的作用。总之，我们在此使用高效方法展示了对照和去传入三叉神经核中小胶质细胞可靠的形态计量学数据，我们提出这些方法同样可应用于在不同生理或病理条件下对这些细胞的任何形态计量学群体分析。
