Paquet M, Tremblay M, Soghomonian J J, Smith Y
Centre de Recherche en Neurobiologie, Hôpital de l'Enfant-Jésus, Université Laval, Québec, Canada G1J 1Z4.
J Neurosci. 1997 Feb 15;17(4):1377-96. doi: 10.1523/JNEUROSCI.17-04-01377.1997.
The objective of the present study was to analyze the cellular and subcellular localization of ionotropic glutamate receptor subunits in midbrain dopaminergic neurons in the squirrel monkey. This was achieved by means of immunohistochemistry at light and electron microscopic levels and in situ hybridization histochemistry. Colocalization studies show that nearly all dopaminergic neurons in both the ventral and dorsal tiers of the substantia nigra compacta (SNc-v, SNc-d) and the ventral tegmental area (VTA) are immunoreactive for AMPA (GluR1, GluR2/3, and GluR4) and NMDAR1 receptor subunits, but not for NMDAR2A/B subunits. The immunoreactivity of the receptor subunits is associated mainly with perikarya and dendritic shafts. Apart from the intensity of immunolabeling for the GluR4 subunit, which is quite similar for the different groups of midbrain dopaminergic neurons, the overall intensity of immunostaining for the other subunits is higher in the SNc-v and SNc-d than in the VTA. In line with these observations, in situ hybridization shows that the average level of labeling for the GluR2 and NMDAR1 subunit mRNAs is significantly higher in the SNc-v than in the VTA, and for the NMDAR1 subunit, higher in the SNc-v than in the SNc-d. In contrast, no significant difference was found for the level of GluR1 mRNA labeling among the three groups of midbrain dopaminergic neurons. At the subcellular level in the SNc-v, AMPA (GluR1 and GluR2/3) and NMDAR1 receptor subunit immunoreactivity is preferentially associated with the postsynaptic densities of asymmetric synapses, but occasionally some immunoreactivity is found along nonsynaptic portions of plasma membranes of dendrites. A small number of preterminal axons, axon terminals, and glial cell processes are also immunoreactive. Our observations indicate that the different groups of midbrain dopaminergic neurons in primates exhibit a certain degree of heterogeneity with regard to the level of expression of some ionotropic glutamate receptor subunits. The widespread neuronal and glial localization of glutamate receptor subunits suggests that excitatory amino acids may act at different levels to control the basal activity and, possibly, to participate in the degeneration of midbrain dopaminergic neurons in Parkinson's disease.
本研究的目的是分析松鼠猴中脑多巴胺能神经元中离子型谷氨酸受体亚基的细胞和亚细胞定位。这是通过光镜和电镜水平的免疫组织化学以及原位杂交组织化学来实现的。共定位研究表明，黑质致密部腹侧层和背侧层（SNc-v、SNc-d）以及腹侧被盖区（VTA）中几乎所有的多巴胺能神经元对AMPA（GluR1、GluR2/3和GluR4）和NMDAR1受体亚基呈免疫反应，但对NMDAR2A/B亚基无免疫反应。受体亚基的免疫反应性主要与胞体和树突干相关。除了GluR4亚基的免疫标记强度在不同组的中脑多巴胺能神经元中相当相似外，SNc-v和SNc-d中其他亚基的免疫染色总体强度高于VTA。与这些观察结果一致，原位杂交显示，SNc-v中GluR2和NMDAR1亚基mRNA的平均标记水平显著高于VTA，对于NMDAR1亚基，SNc-v高于SNc-d。相比之下，在三组中脑多巴胺能神经元中，GluR1 mRNA标记水平未发现显著差异。在SNc-v的亚细胞水平上，AMPA（GluR1和GluR2/3）和NMDAR1受体亚基的免疫反应性优先与不对称突触的突触后密度相关，但偶尔在树突质膜的非突触部分也发现一些免疫反应性。少数终末前轴突、轴突终末和胶质细胞突起也呈免疫反应性。我们的观察结果表明，灵长类动物中不同组的中脑多巴胺能神经元在某些离子型谷氨酸受体亚基的表达水平上表现出一定程度的异质性。谷氨酸受体亚基在神经元和胶质细胞中的广泛定位表明，兴奋性氨基酸可能在不同水平起作用，以控制基础活动，并可能参与帕金森病中脑多巴胺能神经元的变性。
