Cavazos José E, Zhang Peisu, Qazi Romena, Sutula Thomas P
Department of Medicine (Neurology), University of Texas Health Science Center, San Antonio, Texas 78229-3900, USA.
J Comp Neurol. 2003 Apr 7;458(3):272-92. doi: 10.1002/cne.10581.
The mossy fiber pathway in the dentate gyrus undergoes sprouting and synaptic reorganization in response to seizures. The types of new synapses, their location and number, and the identity of their postsynaptic targets determine the functional properties of the reorganized circuitry. The goal of this study was to characterize the types and proportions of sprouted mossy fiber synapses in kindled and kainic acid-treated rats. In normal rats, synapses labeled by Timm histochemistry or dynorphin immunohistochemistry were rarely observed in the supragranular region of the inner molecular layer when examined by electron microscopy. In epileptic rats, sprouted mossy fiber synaptic terminals were frequently observed. The ultrastructural analysis of the types of sprouted synapses revealed that 1) in the supragranular region, labeled synaptic profiles were more frequently axospinous than axodendritic, and many axospinous synapses were perforated; 2) sprouted mossy fiber synaptic terminals formed exclusively asymmetric, putatively excitatory synapses with dendritic spines and shafts in the supragranular region and with the soma of granule cells in the granule cell layer; 3) in contrast to the large sprouted mossy fiber synapses in resected human epileptic hippocampus, the synapses formed by sprouted mossy fibers in rats were smaller; and 4) in several cases, the postsynaptic targets of sprouted synapses were identified as granule cells, but, in one case, a sprouted synaptic terminal formed a synapse with an inhibitory interneuron. The results demonstrate that axospinous asymmetric synapses are the most common type of synapse formed by sprouted mossy fiber terminals, supporting the viewpoint that most sprouted mossy fibers contribute to recurrent excitation in epilepsy.
齿状回中的苔藓纤维通路会因癫痫发作而发生发芽和突触重组。新突触的类型、其位置和数量以及突触后靶点的身份决定了重组电路的功能特性。本研究的目的是表征点燃和 kainic 酸处理大鼠中发芽的苔藓纤维突触的类型和比例。在正常大鼠中，通过电子显微镜检查时，在内分子层的颗粒上层区域很少观察到用 Timm 组织化学或强啡肽免疫组织化学标记的突触。在癫痫大鼠中，经常观察到发芽的苔藓纤维突触终末。对发芽突触类型的超微结构分析表明：1）在颗粒上层区域，标记的突触形态更多是轴棘突触而非轴树突触，并且许多轴棘突触是穿孔的；2）发芽的苔藓纤维突触终末仅与颗粒上层区域的树突棘和树突干以及颗粒细胞层中的颗粒细胞胞体形成不对称的、推测为兴奋性的突触；3）与切除的人类癫痫海马中较大的发芽苔藓纤维突触不同，大鼠中发芽的苔藓纤维形成的突触较小；4）在一些情况下，发芽突触的突触后靶点被确定为颗粒细胞，但在一个案例中，一个发芽的突触终末与一个抑制性中间神经元形成了突触。结果表明轴棘不对称突触是发芽的苔藓纤维终末形成的最常见突触类型，支持了大多数发芽的苔藓纤维在癫痫中促成反复兴奋的观点。
