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The term Cajal–Retzius cells (CR cells) has nowadays been used to identify a heterogeneous population of morphologically and molecularly distinct reelin-producing cell types in the marginal zone/layer I of the developmental cerebral cortex and in the immature hippocampus of different species and at different times during embryogenesis and postnatal life. These cells were discovered by two scientists, Cajal and Retzius, at two different times and in different species. They are originated in the developing brain in multiple sites within the neocortex and hippocampus. From there, CR cells experience migration through the marginal zone, originating the layer I of the cortex. As these cells are involved in the correct organization of the developing brain, there are several studies implicating CR cells in neurodevelopmental disorders, especially Alzheimer’s, schizophrenia, bipolar disorder, autism, lissencephaly and temporal lobe epilepsy. ==History== In 1891 Santiago Ramón y Cajal described slender horizontal bipolar cells he had found in an histological preparation of the developing marginal zone of lagomorphs. These cells were then considered by Gustaf Retzius as homologous to the ones he had found in the marginal zone of human fetuses around mid-gestation in 1893 and 1894. He described those cells as having large, horizontal, sometimes vertically orientated somata located at some distance from the pia. Later on in 1899, Cajal drew the neurons in layer I of the human fetus at term and newborn. The cells laid closer to the pia and displayed smaller, often triangular or pyriform somata, and less complex processes that lacked the ascending branchlets and had a more superficial location than the cells Retzius previously described, The cells' different morphologies and the fact that Cajal and Retzius used different species at different developmental periods led to discussion about the definition of Cajal–Retzius cells. In fact immunohistochemical studies performed at advanced developmental stages in human and macaque cortex visualize cells more similar to the cells Cajal described.〔 In contrast, studies of the human mid-gestation period describe cells closer to the Retzius type. The early descriptions by Cajal and Retzius referred to the neocortex but similar cells were found since 1994 in the marginal zone of the hippocampus.〔〔 Various studies then proved the Cajal–Retzius cells as being responsible for the production of reelin,〔 In 1999 Meyer loosely defined the Cajal–Retzius cells as the family of Reln-immunoreactive neurons in the marginal zone, as so to settle a difference between the pioneer neurons, Reln-negative preplate derivatives that settle in the same area and project to the subcortical area that he had already described in 1998. He also described simpler cells with simpler morphologies in the marginal zone of rodents.〔 In 2005 Bielle suggested that there were distinct subpopulations of Cajal–Retzius cells in different territories of the developing cortex due to the heterogeneity of transcription factors and the discovery of new sites of origin. However, a clear classification scheme as so far not been established. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Cajal–Retzius cell」の詳細全文を読む スポンサード リンク
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