Differential nuclear architecture of striatal neuron populations

<strong>Background:</strong> The striatum is composed by five different neuronal populations of which the MSNs constitute the major cell type (~95%). The remaining ~5% of the striatal neurons comprise aspiny interneurons, which have been classified on the basis of their morphology, protein content and electrophysiological properties as large cholinergic interneurons and somatostatin-, parvalbumin- and calretinin-expressing GABAergic interneurons. In addition to these discriminative features, we showed that nuclear morphology is also particular for each striatal cell type (Matamales/Bertran-Gonzalez et al., 2009). Indeed, the characteristic nuclear architecture of striatal populations is evident on DNA staining with TO-PRO-3, which reveals differences regarding the nuclear diameter, the nuclear shape and the pattern of heterochromatin distribution. Thus, nuclear staining with TO-PRO-3 provides a simple means for the identification of MSNs in the absence of other markers. In addition, the other striatal neurons also have distinct nuclear staining patterns, which allow a good prediction of their nature. This method may be useful to identify striatal neurons in tissue sections and potentially in living tissue, using vital DNA fluorescent dyes. With this simple method we carefully quantified striatal neuronal populations and we clearly showed that all MSNs express either D1R or D2R or both. It will be worth to test whether nuclear architecture in striatal neurons is linked to differences in rates of transcriptional activity. In addition, it will be interesting to analyze whether a correlation between the organization of the nucleus of striatal neurons and their characteristic neuronal activity exists. <strong>Figure Legend: </strong> (A-E) Schematic view of striatal neurons nuclear morphology: (A), MSNs; (B), Parvalbumin interneurons; (C), Calretinin interneurons; (D), Somatostatin interneurons; (E), Cholinergic interneurons. The three different features that allow the identification of striatal neuronal populations based on their nuclear architecture are represented: blue line designates nuclear shape; dashed green line and numbers indicate average nuclear diameter (μm); red dots are DNA chromocenters; red line represents heterochromatin rim. For details, see Matamales/Bertran-Gonzalez et al., 2009.

背景：纹状体（striatum）由五种不同的神经元群体构成，其中中等多棘神经元（MSNs）为主要细胞类型，占比约95%。剩余约5%的纹状体神经元为无棘中间神经元，这类神经元可根据其形态、蛋白质表达谱及电生理特性分为大型胆碱能中间神经元，以及表达生长抑素、小白蛋白和钙视网膜蛋白的γ-氨基丁酸能（GABAergic）中间神经元。除上述鉴别特征外，本研究证实细胞核形态亦是区分不同纹状体细胞类型的特有标志（Matamales/Bertran-Gonzalez等，2009）。事实上，纹状体神经元群体的特征性核结构在经TO-PRO-3进行DNA染色后可清晰显现，该染色可展示细胞核直径、核形态及异染色质分布模式的差异。因此，在缺乏其他标记物的情况下，采用TO-PRO-3进行核染色是鉴定中等多棘神经元的简便方法。此外，其他纹状体神经元也具有独特的核染色模式，可较为准确地预判其细胞类型。该方法可借助活性DNA荧光染料，用于组织切片乃至活组织内的纹状体神经元鉴定。本研究通过该简便方法对纹状体神经元群体进行了精准定量，并明确证实所有中等多棘神经元均表达D1R、D2R，或共表达二者。探究纹状体神经元的核结构是否与转录活性速率差异存在关联，具备重要研究价值。此外，分析纹状体神经元的核组织与其特征性神经元活动之间是否存在相关性，亦是一项颇具意义的研究方向。
图注：(A-E) 纹状体神经元核形态示意图：(A) 中等多棘神经元（MSNs）；(B) 小白蛋白中间神经元；(C) 钙视网膜蛋白中间神经元；(D) 生长抑素中间神经元；(E) 胆碱能中间神经元。本图展示了基于核结构鉴定纹状体神经元群体的三项特征：蓝色线条标示核形态；绿色虚线及数字代表平均细胞核直径（μm）；红色圆点为DNA染色质中心；红色线条表示异染色质边缘。详细信息参见Matamales/Bertran-Gonzalez等，2009年的研究。