Blasco-Ibáñez J M, Martínez-Guijarro F J, Freund T F
Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary.
Eur J Neurosci. 1998 May;10(5):1784-95. doi: 10.1046/j.1460-9568.1998.00190.x.
Enkephalins are known to have a profound effect on hippocampal inhibition, but the possible endogenous source of these neuropeptides, and their relationship to inhibitory interneurons is still to be identified. In the present study we analysed the morphological characteristics of met-enkephalin-immunoreactive cells in the CA1 region of the rat and guinea-pig hippocampus, their coexistence with other neuronal markers and their target selectivity at the light and electron microscopic levels. Several interneurons in all subfields of the hippocampus were found to be immunoreactive for met-enkephalin. In the guinea-pig, fibres arising from immunoreactive interneurons were seen to form a plexus in the stratum oriens/alveus border zone, and basket-like arrays of boutons on both enkephalin-immunoreactive and immunonegative cell bodies in all strata. Immunoreactive boutons always established symmetric synaptic contacts on somata and dendritic shafts. Enkephalin-immunoreactive cells co-localized GABA, vasoactive intestinal polypeptide and calretinin. Postembedding immunogold staining for GABA showed that all the analysed enkephalin-immunoreactive boutons contacted GABAergic postsynaptic structures. In double-immunostained sections, enkephalin-positive axons were seen to innervate calbindin D28k-, somatostatin-, calretinin- and vasoactive intestinal polypeptideimmunoreactive cells with multiple contacts. Based on these characteristics, enkephalin-containing cells in the hippocampus are classified as interneurons specialized to innervate other interneurons, and represent a subset of vasoactive intestinal polypeptide- and calretinin-containing cells. The striking match of ligand and receptor distribution in the case of enkephalin-mediated interneuronal communication suggests that this neuropeptide may play an important role in the synchronization and timing of inhibition involved in rhythmic network activities of the hippocampus.
脑啡肽对海马抑制作用具有深远影响，但其这些神经肽的内源性来源及其与抑制性中间神经元的关系仍有待确定。在本研究中，我们分析了大鼠和豚鼠海马CA1区甲硫氨酸脑啡肽免疫反应性细胞的形态特征、它们与其他神经元标志物的共存情况以及在光镜和电镜水平上的靶标选择性。发现在海马所有亚区的几个中间神经元对甲硫氨酸脑啡肽呈免疫反应性。在豚鼠中，来自免疫反应性中间神经元的纤维在原层/肺泡边界区形成一个丛，并在所有层的脑啡肽免疫反应性和免疫阴性细胞体上形成篮状的终扣阵列。免疫反应性终扣总是在胞体和树突轴上建立对称的突触联系。脑啡肽免疫反应性细胞共定位有γ-氨基丁酸（GABA）、血管活性肠肽和钙视网膜蛋白。对GABA进行包埋后免疫金染色显示，所有分析的脑啡肽免疫反应性终扣均与GABA能突触后结构接触。在双重免疫染色切片中，可见脑啡肽阳性轴突以多个接触点支配钙结合蛋白D28k、生长抑素、钙视网膜蛋白和血管活性肠肽免疫反应性细胞。基于这些特征，海马中含脑啡肽的细胞被归类为专门支配其他中间神经元的中间神经元，并代表含血管活性肠肽和钙视网膜蛋白细胞的一个子集。在脑啡肽介导的中间神经元通讯中，配体和受体分布的显著匹配表明，这种神经肽可能在海马节律性网络活动中参与的抑制同步和定时中发挥重要作用。
