Happe H K, Morley B J
Neurochemistry Laboratory, Boys Town National Research Hospital, Omaha, Nebraska 68131, USA.
J Comp Neurol. 1998 Jul 27;397(2):163-80. doi: 10.1002/(sici)1096-9861(19980727)397:2<163::aid-cne2>3.0.co;2-z.
The cochlear nucleus (CN) is the first site in the central nervous system (CNS) for processing auditory information. Acetylcholine in the CN is primarily extrinsic and is an important neurotransmitter in efferent pathways thought to provide CNS modulation of afferent signal processing. Although muscarinic acetylcholine receptors have been studied in the CN, the role of nicotinic receptors has not. We examined the distribution of one nicotinic acetylcholine receptor subtype, the alpha-bungarotoxin receptor (alpha Bgt), in the CN. Quantitative autoradiography was used to localize receptors and in situ hybridization was used to localize alpha 7 mRNA in CN neurons that express the alpha Bgt receptor. Binding sites for alpha Bgt are abundant in the anterior ventral, posterior ventral, and dorsal divisions of the CN, and receptor density is low in the granule cell layer and interstitial nucleus. Heterogeneity in CN subregions is described. Four distinct patterns of alpha Bgt binding were observed: (1) binding over and around neuronal cell bodies, (2) receptors locally surrounding neurons, (3) dense punctate binding in the dorsal CN (DCN) not associated with neuronal cell bodies, and (4) diffuse fields of alpha Bgt receptors prominent in the DCN molecular layer, a field underlying the granule cell layer and in the medial sheet. The perikaryial receptors are abundant in the ventral CN (VCN) and are always associated with neurons expressing mRNA for the receptor. Other neurons in the VCN also express alpha 7 mRNA, but without alpha Bgt receptor expression associated with the cell body. In general, alpha Bgt receptor distribution parallels cholinergic terminal distribution, except in granule cell regions rich in cholinergic markers but low in alpha Bgt receptors. The findings indicate that alpha Bgt receptors are widespread in the CN but are selectively localized on somata, proximal dendrites, or distal dendrites depending on the specific CN subregion. The data are consistent with the hypothesis that descending cholinergic fibers modulate afferent auditory signals by regulating intracellular Ca2+ through alpha Bgt receptors.
耳蜗核（CN）是中枢神经系统（CNS）中处理听觉信息的首个部位。CN中的乙酰胆碱主要是外源性的，并且是传出通路中的一种重要神经递质，被认为可对传入信号处理提供中枢神经系统调节。尽管已经对CN中的毒蕈碱型乙酰胆碱受体进行了研究，但烟碱型受体的作用尚未得到研究。我们研究了一种烟碱型乙酰胆碱受体亚型——α-银环蛇毒素受体（αBgt）在CN中的分布。采用定量放射自显影法定位受体，并用原位杂交法在表达αBgt受体的CN神经元中定位α7 mRNA。αBgt的结合位点在CN的前腹侧、后腹侧和背侧区丰富，而在颗粒细胞层和间质核中受体密度较低。描述了CN亚区的异质性。观察到四种不同的αBgt结合模式：（1）在神经元细胞体及其周围的结合；（2）局部围绕神经元的受体；（3）在背侧CN（DCN）中与神经元细胞体无关的密集点状结合；（4）αBgt受体的弥漫性区域在DCN分子层中突出，该区域位于颗粒细胞层下方和内侧片层。胞周受体在腹侧CN（VCN）中丰富，并且总是与表达该受体mRNA的神经元相关。VCN中的其他神经元也表达α7 mRNA，但细胞体没有αBgt受体表达。一般来说，αBgt受体分布与胆碱能终末分布平行，除了在富含胆碱能标记物但αBgt受体较少的颗粒细胞区域。这些发现表明，αBgt受体在CN中广泛分布，但根据特定的CN亚区选择性地定位于胞体、近端树突或远端树突上。这些数据与以下假设一致，即下行胆碱能纤维通过αBgt受体调节细胞内Ca2+来调节传入听觉信号。
