Fukuda T, Aika Y, Heizmann C W, Kosaka T
Department of Anatomy and Neurobiology, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Neurosci Res. 1996 Oct;26(2):181-94. doi: 10.1016/s0168-0102(96)01102-9.
GABAergic neurons in the hippocampus proper are greatly diverse in their morphological and physiological features. In the present study we examined whether or not they are also diverse regarding the density of GABAergic input on their somata. GABAergic neurons were immunocytochemically identified with antibodies against glutamic acid decarboxylase (GAD), and the densities of GAD-immunoreactive (GAD-IR) boutons that abutted on GAD-IR somata were estimated by conventional light microscopic, combined light and electron microscopic, and confocal laser scanning microscopic analyses. GAD-IR somata were apparently diverse regarding the density of GABAergic input on them, and those surrounded by higher densities of GAD-IR boutons were distributed mainly in the strata pyramidale and oriens of the CA3 and CA1 regions and could be correlated to a parvalbumin (PV)-IR subpopulation of GABAergic neurons. Quantitative analysis clearly revealed the statistically significant difference between PV-positive and PV-negative GAD-IR neurons in the densities of their somatic GAD-IR boutons. Particularly, most of PV-IR neurons in the CA3 stratum pyramidale as well as some in other layers are characterized by an exceedingly high density of perisomatic GAD-IR boutons. Furthermore, the majority of GAD-IR boutons on PV-IR somata in the stratum pyramidale were also PV-IR. Bilateral transection of the fimbria-fornix, which was supposed to remove GABAergic afferents from the septum, had only partial effects on the densities of PV-IR boutons on PV-IR somata, indicating these PV-IR boutons mainly originated from intrinsic PV-IR neurons. These observations indicate the dense mutual connection between PV-IR GABAergic neurons through perisomatic synaptic contacts, particularly in the stratum pyramidale.
海马体中真正的γ-氨基丁酸能神经元在形态和生理特征上具有极大的多样性。在本研究中，我们检测了这些神经元在其胞体上γ-氨基丁酸能输入的密度方面是否也存在差异。通过使用抗谷氨酸脱羧酶（GAD）的抗体对γ-氨基丁酸能神经元进行免疫细胞化学鉴定，并通过传统光学显微镜、光学和电子显微镜联合以及共聚焦激光扫描显微镜分析，估计了与γ-氨基丁酸能免疫反应性（GAD-IR）胞体相邻的GAD-IR终扣的密度。GAD-IR胞体在其γ-氨基丁酸能输入密度方面显然存在差异，那些被更高密度的GAD-IR终扣包围的胞体主要分布在CA3和CA1区的锥体层和海马层，并且可能与γ-氨基丁酸能神经元的小白蛋白（PV）-IR亚群相关。定量分析清楚地揭示了PV阳性和PV阴性GAD-IR神经元在其胞体GAD-IR终扣密度上的统计学显著差异。特别是，CA3锥体层中的大多数PV-IR神经元以及其他层中的一些神经元的特征是其胞体周围GAD-IR终扣的密度极高。此外，锥体层中PV-IR胞体上的大多数GAD-IR终扣也是PV-IR。穹窿海马伞的双侧横断，这被认为会去除来自隔区的γ-氨基丁酸能传入纤维，对PV-IR胞体上PV-IR终扣的密度只有部分影响，表明这些PV-IR终扣主要起源于内在的PV-IR神经元。这些观察结果表明PV-IRγ-氨基丁酸能神经元之间通过胞体周围突触联系存在紧密的相互连接，特别是在锥体层。
