Ábrahám Hajnalka, Vincze András, Veszprémi Béla, Kravják András, Gömöri Éva, Kovács Gábor G, Seress László
Central Electron Microscopic Laboratory, University of Pécs, Medical School, 7643 Pécs, Szigeti str. 12, Hungary.
Int J Dev Neurosci. 2012 Apr;30(2):147-58. doi: 10.1016/j.ijdevneu.2011.11.005. Epub 2011 Dec 6.
Myelination is considered as one of the last steps of neuronal development and is essential to the physiologically matured function of afferent and efferent pathways. In the present study, myelin formation was examined in the human fetal, postnatal and adult hippocampal formation in Down syndrome and in age-matched controls with immunohistochemistry detecting a protein component of the myelin sheath, the myelin basic protein synthesized by oligodendroglial cells. Myelination is mainly a postnatal event in the hippocampal formation of both healthy controls and in patients with Down syndrome. In patients with Down syndrome the sequence of myelination of the hippocampal formation followed a similar developmental pattern to that in controls. However, myelin formation was generally delayed in Down syndrome compared to age-matched controls. In addition, in the hilus of the dentate gyrus a decreased density of myelinated axons was detected from the start of myelination until adulthood. The majority of local axons (mossy fibers) are not myelinated in the hilar region and myelinated fibers arriving in the hilus come mainly from the subcortical septal nuclei. Since intact septo-hippocampal connections are necessary for memory formation, we hypothesize that decreased myelination in the hilus may contribute to the mental retardation of Down syndrome patients.
髓鞘形成被认为是神经元发育的最后步骤之一，对于传入和传出通路的生理成熟功能至关重要。在本研究中，采用免疫组织化学方法检测髓鞘的一种蛋白质成分，即少突胶质细胞合成的髓鞘碱性蛋白，对唐氏综合征患者以及年龄匹配的对照者的人类胎儿期、出生后及成年期海马结构中的髓鞘形成进行了检测。在健康对照者和唐氏综合征患者的海马结构中，髓鞘形成主要是出生后的事件。在唐氏综合征患者中，海马结构的髓鞘形成顺序遵循与对照者相似的发育模式。然而，与年龄匹配的对照者相比，唐氏综合征患者的髓鞘形成普遍延迟。此外，在齿状回的门区，从髓鞘形成开始直至成年期，均检测到有髓轴突密度降低。门区的大多数局部轴突（苔藓纤维）未被髓鞘化，到达门区的有髓纤维主要来自皮质下隔核。由于完整的隔 - 海马连接对于记忆形成是必要的，我们推测门区髓鞘形成减少可能导致唐氏综合征患者智力发育迟缓。
