Dashtipour K, Tran P H, Okazaki M M, Nadler J V, Ribak C E
Department of Anatomy and Neurobiology, University of California at Irvine, College of Medicine, Irvine, CA 92697-1275, USA.
Brain Res. 2001 Feb 2;890(2):261-71. doi: 10.1016/s0006-8993(00)03119-x.
Several investigators have shown the existence of dentate granule cells in ectopic locations within the hilus and molecular layer using both Golgi and retrograde tracing studies but the ultrastructural features and synaptic connections of ectopic granule cells were not previously examined. In the present study, the biocytin retrograde tracing technique was used to label ectopic granule cells following injections into stratum lucidum of CA3b of hippocampal slices obtained from epileptic rats. Electron microscopy was used to study hilar ectopic granule cells that were located 20-40 microm from the granule cell layer (GCL). They had ultrastructural features similar to those of granule cells in the GCL but showed differences, including nuclei that often displayed infoldings and thicker apical dendrites. At their origin, these dendrites were 6 microm in diameter and they tapered down to 2 microm at the border with the GCL. Both biocytin-labeled and unlabeled axon terminals formed exclusively asymmetric synapses with the somata and proximal dendrites of hilar ectopic granule cells. The mean number of axosomatic synapses for these cells was three times that for granule cells in the GCL. Together, these data indicate that hilar ectopic granule cells are postsynaptic to mossy fibers and have less inhibitory input on their somata and proximal dendrites than granule cells in the GCL. This finding is consistent with recent physiological results showing that hilar ectopic granule cells from epileptic rats are more hyperexcitable than granule cells in the GCL.
几位研究者利用高尔基染色法和逆行示踪研究，证实了在海马体门区和分子层的异位位置存在齿状颗粒细胞，但此前尚未对异位颗粒细胞的超微结构特征和突触连接进行研究。在本研究中，采用生物素逆行示踪技术，对取自癫痫大鼠的海马切片CA3b区透明层注射后标记异位颗粒细胞。利用电子显微镜研究距颗粒细胞层（GCL）20 - 40微米的门区异位颗粒细胞。它们具有与GCL中颗粒细胞相似的超微结构特征，但也存在差异，包括细胞核常出现褶皱以及顶端树突更粗。这些树突起始处直径为6微米，在与GCL交界处逐渐变细至2微米。生物素标记和未标记的轴突终末均仅与门区异位颗粒细胞的胞体和近端树突形成不对称突触。这些细胞的轴体突触平均数量是GCL中颗粒细胞的三倍。这些数据共同表明，门区异位颗粒细胞是苔藓纤维的突触后神经元，其胞体和近端树突上的抑制性输入比GCL中的颗粒细胞少。这一发现与最近的生理学结果一致，即癫痫大鼠的门区异位颗粒细胞比GCL中的颗粒细胞更易兴奋。
