Ito Tetsufumi, Atoji Yasuro
Department of Anatomy, Faculty of Medical Sciences, University of Fukui, Eiheiji, Fukui, 910-1193, Japan.
Research and Education Program for Life Science, University of Fukui, Fukui, Fukui, 910-8507, Japan.
J Comp Neurol. 2016 Sep 1;524(13):2604-22. doi: 10.1002/cne.23979. Epub 2016 Feb 29.
Inhibitory feedforward projection is one of key features of the organization of the central auditory system. In mammals, the inferior colliculus (IC) is the origin of a substantial inhibitory feedforward projection as well as an excitatory projection to the auditory thalamus. This inhibitory feedforward projection is provided by large γ-aminobutyric acid (GABA)ergic (LG) neurons, which are characterized by their receipt of dense excitatory axosomatic terminals positive for vesicular glutamate transporter (VGLUT) 2. In the avian torus semicircularis (TS), which is the homolog of the IC, neither the homology of cell types nor the presence of inhibitory feedforward inhibition have been established. In this study, we tested the presence of LG neurons in pigeon and chicken by neuroanatomical techniques. The TS contained two types of GABAergic neurons of different soma size. Of these, larger GABA + cells were encircled by dense VGLUT2 + axosomatic terminals. Ultrastructural analyses revealed that more than 30% of the perimeter of a large GABA+, but not small GABA + or GABA-, soma was covered by presumptive excitatory axosomatic terminals, suggesting that large GABA + cells are the sole recipient of dense excitatory axosomatic synapses. After injection of a retrograde tracer into the auditory thalamus, many retrogradely labeled neurons were found bilaterally in the TS, a few of which were GABA+. Almost all tectothalamic GABA + neurons had large somata, and received dense VGLUT2 + axosomatic terminals. These results clearly demonstrated the presence of LG neurons in birds. The similar morphology of LG neurons implies that the function of tectothalamic inhibition is similar among amniotes. J. Comp. Neurol. 524:2604-2622, 2016. © 2016 Wiley Periodicals, Inc.
抑制性前馈投射是中枢听觉系统组织的关键特征之一。在哺乳动物中，下丘（IC）是大量抑制性前馈投射的起源，也是向听觉丘脑的兴奋性投射的起源。这种抑制性前馈投射由大型γ-氨基丁酸（GABA）能（LG）神经元提供，其特征是接收对囊泡谷氨酸转运体（VGLUT）2呈阳性的密集兴奋性轴突体终末。在与IC同源的鸟类半规管隆起（TS）中，细胞类型的同源性以及抑制性前馈抑制的存在均未得到证实。在本研究中，我们通过神经解剖学技术检测了鸽子和鸡中LG神经元的存在情况。TS包含两种不同胞体大小的GABA能神经元。其中，较大的GABA⁺细胞被密集的VGLUT2⁺轴突体终末环绕。超微结构分析显示，大型GABA⁺细胞（而非小型GABA⁺或GABA⁻细胞）胞体周长的30%以上被推测为兴奋性轴突体终末覆盖，这表明大型GABA⁺细胞是密集兴奋性轴突体突触的唯一接受者。将逆行示踪剂注入听觉丘脑后，在TS双侧发现了许多逆行标记的神经元，其中少数为GABA⁺。几乎所有顶盖丘脑GABA⁺神经元都有大型胞体，并接受密集的VGLUT2⁺轴突体终末。这些结果清楚地证明了鸟类中存在LG神经元。LG神经元的相似形态意味着羊膜动物中顶盖丘脑抑制的功能相似。《比较神经学杂志》524:2604 - 2622，2016年。©2016威利期刊公司
