Department of Anatomy, Faculty of Medical Sciences, University of Fukui Eiheiji, Japan.
Front Neural Circuits. 2012 Jul 26;6:48. doi: 10.3389/fncir.2012.00048. eCollection 2012.
The inferior colliculus (IC) in the midbrain of the auditory system uses a unique basic circuit to organize the inputs from virtually all of the lower auditory brainstem and transmit this information to the medial geniculate body (MGB) in the thalamus. Here, we review the basic circuit of the IC, the neuronal types, the organization of their inputs and outputs. We specifically discuss the large GABAergic (LG) neurons and how they differ from the small GABAergic (SG) and the more numerous glutamatergic neurons. The somata and dendrites of LG neurons are identified by axosomatic glutamatergic synapses that are lacking in the other cell types and exclusively contain the glutamate transporter VGLUT2. Although LG neurons are most numerous in the central nucleus of the IC (ICC), an analysis of their distribution suggests that they are not specifically associated with one set of ascending inputs. The inputs to ICC may be organized into functional zones with different subsets of brainstem inputs, but each zone may contain the same three neuron types. However, the sources of VGLUT2 axosomatic terminals on the LG neuron are not known. Neurons in the dorsal cochlear nucleus, superior olivary complex, intermediate nucleus of the lateral lemniscus, and IC itself that express the gene for VGLUT2 only are the likely origin of the dense VGLUT2 axosomatic terminals on LG tectothalamic neurons. The IC is unique since LG neurons are GABAergic tectothalamic neurons in addition to the numerous glutamatergic tectothalamic neurons. SG neurons evidently target other auditory structures. The basic circuit of the IC and the LG neurons in particular, has implications for the transmission of information about sound through the midbrain to the MGB.
中脑的下丘（IC）在听觉系统中使用独特的基本回路来组织来自几乎所有低级听觉脑干的输入，并将此信息传输到丘脑的内侧膝状体（MGB）。在这里，我们回顾了 IC 的基本回路、神经元类型、它们的输入和输出的组织。我们特别讨论了大型 GABA 能（LG）神经元以及它们与小型 GABA 能（SG）和更多数量的谷氨酸能神经元的区别。LG 神经元的胞体和树突通过轴突-体谷氨酸能突触来识别，而这些突触在其他细胞类型中不存在，并且仅包含谷氨酸转运体 VGLUT2。尽管 LG 神经元在 IC 的中央核（ICC）中数量最多，但对其分布的分析表明，它们与一组特定的上行输入无关。ICC 的输入可能组织成具有不同的脑干输入子集的功能区，但每个区可能包含相同的三种神经元类型。然而，LG 神经元上的 VGLUT2 轴突-体末端的来源尚不清楚。表达 VGLUT2 基因的耳蜗核、上橄榄复合体、外侧丘系中间核和 IC 本身的神经元可能是 LG 听觉丘脑神经元上密集的 VGLUT2 轴突-体末端的来源。IC 是独特的，因为除了众多的谷氨酸能听觉丘脑神经元之外，LG 神经元还是 GABA 能听觉丘脑神经元。SG 神经元显然靶向其他听觉结构。IC 的基本回路和 LG 神经元，特别是，对通过中脑将声音信息传输到 MGB 具有重要意义。
