Claiborne B J, Amaral D G, Cowan W M
J Comp Neurol. 1986 Apr 22;246(4):435-58. doi: 10.1002/cne.902460403.
The axon collaterals of dentate granule cells have been analyzed with the aid of a computerized microscope, following intracellular injections of horseradish peroxidase in hippocampal slice preparations. The axon of each granule cell gives rise to approximately seven primary collaterals; these collaterals usually divide into secondary and tertiary branches, which form an extensive plexus within the hilar region of the dentate gyrus. Individual axon collaterals vary greatly in length, but most have been found to be between 100 and 300 microns long. On average, the summed lengths of the collaterals (exclusive of the parent mossy fiber) are approximately 2,300 microns. Except for an occasional collateral that is given off by a mossy fiber in the proximal part of field CA3 of the hippocampus, the collaterals of the granule cell axons are confined to the hilar region; they are rarely seen in the granule cell layer itself and have never been observed in the molecular layer. In the longitudinal dimension of the dentate gyrus, most of the collaterals are contained within a zone about 400 microns wide. The distribution of the collaterals within the hilar region is correlated with the location of the granule cell body. Those that arise from cells near the tip of the suprapyramidal blade tend to be confined to the region above field CA3; those from cells nearer the crest and from the infrapyramidal blade ramify widely throughout the hilus. Two types of varicosities are present on the collaterals. Numerous small (approximately 2 microns), round varicosities are distributed unevenly along the collaterals; in electron micrographs these varicosities can be seen to make asymmetric synaptic contacts with dendritic shafts. On average, each granule cell collateral plexus has about 160 of these varicosities. The second type of varicosity is irregular in shape and ranges from 2 to 4 microns in diameter; there is usually only one such varicosity per collateral. In all respects except size, these varicosities resemble the expansions found on the parent mossy fibers. Mossy fiber trajectories in the proximal part of field CA3 were studied after extracellular injections of HRP into localized regions of the granule cell layer. Granule cells at different locations around the blade send their mossy fibers to different depths within the pyramidal cell layer in the proximal part of field CA3. However, further distally, mossy fibers from all parts of the granule cell layer contribute to the suprapyramidal bundle that occupies the stratum lucidum.
在海马切片标本中对齿状颗粒细胞的轴突侧支进行了分析，方法是在细胞内注射辣根过氧化物酶后借助计算机显微镜观察。每个颗粒细胞的轴突大约发出7条初级侧支；这些侧支通常会分成次级和三级分支，在齿状回的门区形成一个广泛的神经丛。单个轴突侧支的长度差异很大，但大多数已发现其长度在100至300微米之间。平均而言，侧支（不包括母苔藓纤维）的总长度约为2300微米。除了海马CA3区近端偶尔有一条由苔藓纤维发出的侧支外，颗粒细胞轴突的侧支都局限于门区；在颗粒细胞层本身很少见到它们，在分子层从未观察到。在齿状回的纵向维度上，大多数侧支包含在一个约400微米宽的区域内。侧支在门区内的分布与颗粒细胞体的位置相关。那些起源于上锥体叶片尖端附近细胞的侧支往往局限于CA3区上方的区域；那些来自靠近嵴和下锥体叶片细胞的侧支在整个门区内广泛分支。侧支上有两种类型的曲张。许多小的（约2微米）圆形曲张沿侧支不均匀分布；在电子显微镜照片中，可以看到这些曲张与树突轴形成不对称突触接触。平均而言，每个颗粒细胞侧支神经丛约有160个这样的曲张。第二种曲张形状不规则，直径在2至4微米之间；每个侧支通常只有一个这样的曲张。除了大小外，这些曲张在各方面都类似于母苔藓纤维上的膨大部。在颗粒细胞层的局部区域进行细胞外注射HRP后，研究了CA3区近端的苔藓纤维轨迹。围绕叶片不同位置的颗粒细胞将其苔藓纤维发送到CA3区近端锥体细胞层内的不同深度。然而，在更远端，来自颗粒细胞层所有部分的苔藓纤维都汇入占据透明层的上锥体束。
