Martínez A, Lübke J, Del Río J A, Soriano E, Frotscher M
Department of Animal and Plant Cell Biology, Faculty of Biology, University of Barcelona, Spain.
J Comp Neurol. 1996 Dec 2;376(1):28-44. doi: 10.1002/(SICI)1096-9861(19961202)376:1<28::AID-CNE2>3.0.CO;2-Q.
Chandelier cells are specialized cortical GABAergic neurons that establish synaptic contacts exclusively with the axon initial segments of principal neurons. They are found in all regions of the hippocampal formation. Here we describe their morphological features in the hilus and in regions CA1 and CA3 by using Golgi/electron microscopy. Attempts were also made to identify the target neurons of chandelier cells in the hilus and entorhinal cortex. Golgi-impregnated chandelier cells display a complex axonal arbor in CA1, with many collaterals forming strings of boutons. The axon plexuses of such cells are less developed in CA3, whereas those in the hilus cover the entire region, although single collaterals are rather simple, with only a few boutons. The dendrites of chandelier cells in CA1 and CA3 have an orientation similar to that of pyramidal cell dendrites and are thus likely to be activated by the same afferent fiber systems. The hilar chandelier cells do not give rise to dendrites invading the molecular layer. Thus, these cells may not receive a dense input from the entorhinal cortex but may be driven by the abundant mossy fiber collaterals in the hilar region. In the CA1 and CA3 regions, the axons of chandelier cells contact the axon initial segments of pyramidal cells. In the hilar region, gold-toned boutons were found to impinge on the initial segments of neurons displaying characteristics of mossy cells. This notion was substantiated by electron microscopic analysis of mossy cells identified by intracellular injection of Lucifer yellow. Those cells regularly showed numerous symmetric synapses on their axon initial segments. Entorhinohippocampal projection cells, identified by injection of horseradish peroxidase into the hippocampus, were found to be preferential targets of chandelier cells in the entorhinal cortex. Our data point to regional variations in chandelier cell morphology and connectivity and indicate that chandelier cells are a principal component of inhibitory mechanisms in all stations of the main excitatory pathway of the hippocampal formation.
吊灯细胞是特殊的皮质γ-氨基丁酸能神经元，仅与主神经元的轴突起始段建立突触联系。它们存在于海马结构的所有区域。在这里，我们通过高尔基/电子显微镜描述了它们在海马齿状回以及CA1和CA3区域的形态特征。我们还尝试识别海马齿状回和内嗅皮质中吊灯细胞的靶神经元。高尔基浸染的吊灯细胞在CA1区显示出复杂的轴突分支，许多侧支形成一连串的终扣。这类细胞的轴突丛在CA3区发育较差，而在海马齿状回中则覆盖整个区域，尽管单个侧支相当简单，只有少数终扣。CA1和CA3区吊灯细胞的树突与锥体细胞树突的方向相似，因此可能被相同的传入纤维系统激活。海马齿状回的吊灯细胞不会产生侵入分子层的树突。因此，这些细胞可能不会从内嗅皮质接收密集的输入，但可能由海马齿状回区域丰富的苔藓纤维侧支驱动。在CA1和CA3区，吊灯细胞的轴突与锥体细胞的轴突起始段接触。在海马齿状回区域，发现金色终扣作用于显示苔藓细胞特征的神经元的起始段。通过对经细胞内注射路西法黄鉴定的苔藓细胞进行电子显微镜分析，证实了这一观点。这些细胞在其轴突起始段经常显示出许多对称突触。通过将辣根过氧化物酶注入海马体鉴定出的内嗅-海马投射细胞，被发现是内嗅皮质中吊灯细胞的优先靶标。我们的数据表明吊灯细胞的形态和连接存在区域差异，并表明吊灯细胞是海马结构主要兴奋性通路所有部位抑制机制的主要组成部分。
