Ceranik K, Bender R, Geiger J R, Monyer H, Jonas P, Frotscher M, Lübke J
Anatomisches Institut I,Albert-Ludwigs-Universität Freiburg, D-79104 Freiburg, Germany.
J Neurosci. 1997 Jul 15;17(14):5380-94. doi: 10.1523/JNEUROSCI.17-14-05380.1997.
The main excitatory pathway of the hippocampal formation is controlled by a network of morphologically distinct populations of GABAergic interneurons. Here we describe a novel type of GABAergic interneuron located in the outer molecular layer (OML) of the rat dentate gyrus with a long-range forward projection from the dentate gyrus to the subiculum across the hippocampal fissure. OML interneurons were recorded in hippocampal slices by using the whole-cell patch-clamp configuration. During recording, cells were filled with biocytin for subsequent light and electron microscopic analysis. Neurons projecting to the subiculum were distributed throughout the entire OML. They had round or ovoid somata and a multipolar dendritic morphology. Two axonal domains could be distinguished: an extensive, tangential distribution within the OML and a long-range vertical and tangential projection to layer 1 and stratum pyramidale of the subiculum. Symmetric synaptic contacts were established by these interneurons on dendritic shafts in the OML and subiculum. OML interneurons were characterized physiologically by short action potential duration and marked afterhyperpolarization that followed the spike. On sustained current injection, they generated high-frequency (up to 130 Hz, 34 degrees C) trains of action potentials with only little adaptation. In situ hybridization and single-cell RT-PCR analysis for GAD67 mRNA confirmed the GABAergic nature of OML interneurons. GABAergic interneurons in the OML projecting to the subiculum connect the input and output regions of the hippocampus. Hence, they could mediate long-range feed-forward inhibition and may participate in an oscillating cross-regional interneuron network that may synchronize the activity of spatially distributed principal neurons in the dentate gyrus and the subiculum.
海马结构的主要兴奋性通路受形态各异的γ-氨基丁酸（GABA）能中间神经元网络控制。在此，我们描述了一种新型的GABA能中间神经元，它位于大鼠齿状回的外分子层（OML），具有从齿状回跨越海马裂向海马下脚的长程前向投射。通过全细胞膜片钳记录配置在海马切片中记录OML中间神经元。记录过程中，细胞用生物胞素填充，以便随后进行光镜和电镜分析。投射到海马下脚的神经元分布于整个OML。它们具有圆形或椭圆形的胞体以及多极树突形态。可区分出两个轴突区域：在OML内广泛的切线分布以及向海马下脚第1层和锥体层的长程垂直和切线投射。这些中间神经元在OML和海马下脚的树突干上建立对称突触联系。OML中间神经元在生理上的特征为动作电位时程短以及动作电位后显著的超极化。持续电流注入时，它们产生高频（高达130 Hz，34℃）的动作电位串，且仅有轻微适应。原位杂交和GAD67 mRNA的单细胞逆转录-聚合酶链反应分析证实了OML中间神经元的GABA能性质。投射到海马下脚的OML中的GABA能中间神经元连接海马的输入和输出区域。因此，它们可能介导长程前馈抑制，并可能参与一个振荡性的跨区域中间神经元网络，该网络可能使齿状回和海马下脚中空间分布的主神经元的活动同步。
