Bilak M M, Bilak S R, Morest D K
Department of Anatomy, University of Connecticut Health Center, Farmington 06030, USA.
Neuroscience. 1996 Dec;75(4):1075-97. doi: 10.1016/0306-4522(96)00197-2.
Glutamate is used in the cochlear nucleus as a neurotransmitter by cochlear nerve synapses and by local circuits of granule cell axons. In the present study, immunocytochemistry and in situ hybridization were used to identify different types of neurons expressing N-methyl-D-aspartate receptor subunit I (NMDAR1) in the mouse cochlear nucleus. N-Methyl-D-aspartate receptor subunit 1 was expressed in most neuronal types, but granule cells in the dorsal cochlear nucleus had little, if any, expression, unlike their heavily labeled counterparts in the small cell shell and cerebellum. The findings do not support an analogy between the dorsal cochlear nucleus and the cerebellar cortex. In the cochlear nucleus the most heavily labeled structures were dendrites in the small cell shell and superficial dorsal cochlear nucleus, including the fusiform cell apical dendrites, which are targets of granule cell axons. However, fusiform cell basal dendrites, which are the synaptic sites of cochlear nerve fibers, did not express N-methyl-D-aspartate receptor subunit 1. Thus different parts of the fusiform cells can have different subunits in their glutamate receptors. Also branches of the same cochlear nerve axons projecting to the octopus, stellate, and bushy cells of the ventral cochlear nucleus can use N-methyl-D-aspartate receptor, while their branches to fusiform cells cannot. Each cochlear nucleus neuron type has a characteristic level of N-methyl-D-aspartate receptor subunit 1 expression. Each type differs in its auditory response properties, which may depend on synaptic activities requiring different glutamate subunit patterns.
谷氨酸在耳蜗核中被用作耳蜗神经突触以及颗粒细胞轴突局部回路的神经递质。在本研究中，采用免疫细胞化学和原位杂交技术来鉴定小鼠耳蜗核中表达N-甲基-D-天冬氨酸受体亚基I（NMDAR1）的不同类型神经元。N-甲基-D-天冬氨酸受体亚基1在大多数神经元类型中都有表达，但耳蜗背核中的颗粒细胞即使有表达也很少，这与它们在小细胞壳层和小脑中有大量标记的对应细胞不同。这些发现不支持耳蜗背核与小脑皮质之间存在类比关系。在耳蜗核中，标记最强烈的结构是小细胞壳层和耳蜗背核浅层的树突，包括梭形细胞的顶端树突，它们是颗粒细胞轴突的靶点。然而，作为耳蜗神经纤维突触部位的梭形细胞基底树突不表达N-甲基-D-天冬氨酸受体亚基1。因此，梭形细胞的不同部分在其谷氨酸受体中可以有不同的亚基。同样，投射到耳蜗腹核的章鱼形细胞、星形细胞和球形细胞的同一耳蜗神经轴突分支可以使用N-甲基-D-天冬氨酸受体，而它们投射到梭形细胞的分支则不能。每种耳蜗核神经元类型都有其特征性的N-甲基-D-天冬氨酸受体亚基1表达水平。每种类型在其听觉反应特性上有所不同，这可能取决于需要不同谷氨酸亚基模式的突触活动。
