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Development of the Hippocampal Formation in the Prenatal Rat

Xi Gangming;Wang Huaqiao;Tang Tingyong;Zhou Lihua (Department of Anatomy,Sun Yat-sen University of Medical Science,Guangzhou 510089) (Research Unit of Neurology of Taihc Hospital,Yunyang Medical College,Shiyan 442000)  
For investigation the development of the hippocampal formation in embryonic rats. The immersion-fixed,paraffin section and Nissl stain methods, were used to observe the embryonic hippocampal formation of E14 to E22 days rat. The results showed: The hippocampal rudiment might be distinguished from the dorsomedial wall of the telencephalon as early as E14. On day E16, the hippocampal rudiment was continuous with the subicular neuroepithelium dorsally,and with the septal neuroepithelium and stroma of the choroid plexus ventrally. At this time,three components of the hippocampal rudiment could be identified,namly the Ammonic neuroepithelium dorsally,the primary dentate neruoepithelium beneath it,and the fimbral glioepithelium ventrally. On day E18,the formation of the hippocampal fissure divided the dentate matrix from the Ammonic neuroepithelium. At this stage, the pyramidal layer of CA1 region and the fimbria began to appear;The external limb of the dentate granular layer and the dentate hilus were also beginnig to become morphologically distinct and the cells of the first dentate migration was traceable to the dentate gyrus. On day E22,the hippocampal fissare disappeared and the Ammonic molecular layer fused with the dentate molecular layer; the pyramidal layer of the CA1 region became thickening and expansion;the curved portion of the CA3 region had formed and the leading tip of which was penetrating the parenchyma of the dentate hilus;the Ammonic neuroepithelium and intermediate layer became thinning; the alveus appeared;the external dentate limb became longer and more distinct,and the internal dentate limb began to form ; A large number of cells surrounding the CA3 region were migrating to hilus of the dentate gyrus. It was concluded that the structure of the Ammon's horn had basically formed before birth, but the structure of dentate gyrns was completely formed,only the skeleton of two dentate limb appeared,its larger complement would be produced after birth.
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