Wong Peiyan, Kaas Jon H
Department of Psychology, Vanderbilt University, Nashville, Tennessee, USA.
Anat Rec (Hoboken). 2008 Oct;291(10):1301-33. doi: 10.1002/ar.20758.
Squirrels are highly visual mammals with an expanded cortical visual system and a number of well-differentiated architectonic fields. To describe and delimit cortical fields, subdivisions of cortex were reconstructed from serial brain sections cut in the coronal, sagittal, or horizontal planes. Architectonic characteristics of cortical areas were visualized after brain sections were processed with immunohistochemical and histochemical procedures for revealing parvalbumin, calbindin, neurofilament protein, vesicle glutamate transporter 2, limbic-associated membrane protein, synaptic zinc, cytochrome oxidase, myelin or Nissl substance. In general, these different procedures revealed similar boundaries between areas, suggesting that functionally relevant borders were being detected. The results allowed a more precise demarcation of previously identified areas as well as the identification of areas that had not been previously described. Primary sensory cortical areas were characterized by sparse zinc staining of layer 4, as thalamocortical terminations lack zinc, as well as by layer 4 terminations rich in parvalbumin and vesicle glutamate transporter 2. Primary areas also expressed higher levels of cytochrome oxidase and myelin. Primary motor cortex was associated with large SMI-32 labeled pyramidal cells in layers 3 and 5. Our proposed organization of cortex in gray squirrels includes both similarities and differences to the proposed of cortex in other rodents such as mice and rats. The presence of a number of well-differentiated cortical areas in squirrels may serve as a guide to the identification of homologous fields in other rodents, as well as a useful guide in further studies of cortical organization and function.
松鼠是高度依赖视觉的哺乳动物，具有扩展的皮质视觉系统和许多分化良好的结构区域。为了描述和界定皮质区域，从冠状、矢状或水平平面切割的连续脑切片中重建皮质的细分区域。在用免疫组织化学和组织化学方法处理脑切片以显示小白蛋白、钙结合蛋白、神经丝蛋白、囊泡谷氨酸转运体2、边缘相关膜蛋白、突触锌、细胞色素氧化酶、髓磷脂或尼氏物质后，皮质区域的结构特征得以显现。一般来说，这些不同的方法揭示了区域之间相似的边界，这表明检测到了功能相关的边界。这些结果使得能够更精确地划分先前确定的区域，并识别出先前未描述的区域。初级感觉皮质区域的特征是第4层锌染色稀疏，因为丘脑皮质终末缺乏锌，以及富含小白蛋白和囊泡谷氨酸转运体2的第4层终末。初级区域还表达较高水平的细胞色素氧化酶和髓磷脂。初级运动皮质与第3层和第5层中被SMI-32标记的大锥体细胞相关。我们提出的灰松鼠皮质组织与其他啮齿动物（如小鼠和大鼠）皮质组织既有相似之处，也有不同之处。松鼠中存在许多分化良好的皮质区域，这可能有助于识别其他啮齿动物中的同源区域，也为进一步研究皮质组织和功能提供有用的指导。
