Sørensen T, Zimmer J
Institute of Anatomy B (Neurobiology), University of Aarhus, Denmark.
J Comp Neurol. 1988 Jan 1;267(1):43-54. doi: 10.1002/cne.902670104.
As part of an ultrastructural analysis of the normal rat fascia dentata and intracerebral and intraocular dentate transplants the synapses in the dentate molecular layer were quantified. Hippocampal and dentate tissue from 21-day-old rat embryos were grafted into the brain of developing and adult rats and to the anterior eye chamber of adult rats. After 100 or 200 days of survival the recipient rat brains and the recipient eyes were processed for electron microscopy, and the graft dentate molecular layer with the adjacent granule cell layer selected for ultrastructural analysis. Tissue from the dentate molecular layer of normal adult rats served as controls. The dentate synapses were classified as asymmetric (Gray's type 1) or symmetric (Gray's type 2), and according to the postsynaptic element (cell body, dendritic shaft, dendritic spine). The spine synapses were further classified into simple and complex types according to the spine-terminal configuration. Also, the length of synaptic contacts of the individual synaptic types was measured in some grafts, just as the percentage of the cross sectional area of the neuropil covered by blood vessels. The results showed that the synaptic density, expressed as number per unit area of neuropil, to a large extent was the same within the different parts of the normal dentate molecular layer. Compared with this the synaptic density was reduced with 16.4% in dentate molecular layer of the intracerebral graft, primarily because of a 17.6% reduction of simple synapses on dendritic spines and almost halving of the symmetric synapses on dendritic shafts. The synaptic density was independent of the age of the recipient, the intracerebral location of the graft, and the survival time. Although the synaptic length of some of the individual synaptic types increased, this did not compensate for the loss of synapses. In the intraocular grafts the synaptic density was lower than in the intracerebral grafts. Despite the reduced synaptic density, which mainly involved two synaptic types, we conclude that grafted dentate granule cells can develop a remarkably normal, ultrastructural synaptic organization even in the absence of major afferent inputs. This outcome must accordingly be achieved by reorganization of the available intrinsic afferents.
作为对正常大鼠齿状回以及脑内和眼内齿状移植体进行超微结构分析的一部分，对齿状分子层中的突触进行了定量分析。将21日龄大鼠胚胎的海马和齿状组织移植到发育中和成年大鼠的脑内以及成年大鼠的眼前房。存活100或200天后，对受体大鼠的脑和眼进行电子显微镜处理，并选择移植的齿状分子层及其相邻的颗粒细胞层进行超微结构分析。正常成年大鼠齿状分子层的组织用作对照。齿状突触分为不对称（格雷I型）或对称（格雷II型），并根据突触后成分（细胞体、树突干、树突棘）进行分类。根据棘突-终末结构，棘突突触进一步分为简单型和复杂型。此外，在一些移植体中测量了各个突触类型的突触接触长度，以及神经毡横截面积中被血管覆盖的百分比。结果表明，以每单位神经毡面积的数量表示的突触密度在正常齿状分子层的不同部分在很大程度上是相同的。与此相比，脑内移植体的齿状分子层中突触密度降低了16.4%，主要是因为树突棘上的简单突触减少了17.6%，树突干上的对称突触几乎减半。突触密度与受体年龄、移植体在脑内的位置以及存活时间无关。尽管某些个别突触类型的突触长度增加了，但这并不能弥补突触的损失。眼内移植体中的突触密度低于脑内移植体。尽管突触密度降低，主要涉及两种突触类型，但我们得出结论，即使在没有主要传入输入的情况下，移植的齿状颗粒细胞也能形成明显正常的超微结构突触组织。因此，这一结果必定是通过对可用的固有传入纤维进行重组而实现的。
