Dalmau I, Finsen B, Zimmer J, González B, Castellano B
Department of Cell Biology and Physiology, Universitat Autònoma de Barcelona, Spain.
Hippocampus. 1998;8(5):458-74. doi: 10.1002/(SICI)1098-1063(1998)8:5<458::AID-HIPO6>3.0.CO;2-N.
During the prenatal development of the hippocampus, microglial cell precursors progressively occur in all subfields in accordance with known ontogenetic gradients of the region (Dalmau et al., J. Comp. Neurol. 1997a;377:70-84). The present study follows the regional distribution of these microglial cell precursors and their morphological differentiation in the rat hippocampus from birth to postnatal (P) day 18. The results demonstrate that the cellular differentiation and the subregional distribution of microglia follow the specific developmental gradients of the different parts of Ammon's horn and the dentate gyrus. Microglial cell distribution in the dentate gyrus is thus delayed compared with that in Ammon's horn. The appearance of microglia in the hippocampal subregions and differentiation of cell precursors into adult microglia occur earlier at temporal levels than at septal levels. Distribution of microglial cells follows an outside-to-inside pattern from the hippocampal fissure to the main cell layers in either Ammon's horn or the dentate gyrus. Meanwhile, the resident microglial cells located in the stratum oriens and dentate hilus at birth also increase in number and gradually disperse throughout the whole tissue of the two layers with age. In Ammon's horn, microglial differentiation occurs earlier in CA3 than in CA1. In the dentate gyrus, microglia appear earlier in relation to the external limb than to the internal limb, largely following a lateral-to-medial gradient. The differentiation and appearance of microglia in the various hippocampal and dentate subregions often correspond to the developmental stage of intrinsic and extrinsic afferent nerve fiber projections. Finally, in both Ammon's horn and the dentate gyrus, cells resembling reactive microglia are also observed and, in particular, in the perforant path projections from P9 to P18, suggesting their participation not only in phagocytosis of dead cells but also in axonal elimination and/or fiber reorganization.
在海马体的产前发育过程中，小胶质细胞前体根据该区域已知的个体发生梯度逐渐出现在所有亚区（Dalmau等人，《比较神经学杂志》1997a；377：70 - 84）。本研究追踪了大鼠海马体中这些小胶质细胞前体从出生到出生后（P）第18天的区域分布及其形态分化。结果表明，小胶质细胞的细胞分化和亚区分布遵循海马角和齿状回不同部分的特定发育梯度。因此，齿状回中小胶质细胞的分布比海马角中的延迟。海马亚区中小胶质细胞的出现以及细胞前体向成年小胶质细胞的分化在颞叶水平比在隔区水平更早发生。小胶质细胞的分布从海马裂到海马角或齿状回的主要细胞层遵循由外向内的模式。同时，出生时位于海马体原层和齿状回门区的常驻小胶质细胞数量也随着年龄增长而增加，并逐渐散布到这两层的整个组织中。在海马角中，CA3区的小胶质细胞分化比CA1区更早。在齿状回中，相对于内肢，小胶质细胞在外肢出现得更早，大致遵循从外侧到内侧的梯度。海马体和齿状回各个亚区中小胶质细胞的分化和出现通常与内在和外在传入神经纤维投射的发育阶段相对应。最后，在海马角和齿状回中，也观察到了类似反应性小胶质细胞的细胞，特别是在从出生后第9天到第18天的穿通通路投射中，这表明它们不仅参与死细胞的吞噬作用，还参与轴突消除和/或纤维重组。
