van den Pol A N, Romano C, Ghosh P
Section of Neurosurgery, Yale University Medical School, New Haven, Connecticut 06520, USA.
J Comp Neurol. 1995 Nov 6;362(1):134-50. doi: 10.1002/cne.903620108.
The metabotropic glutamate receptor mGluR5 is a G-protein coupled receptor that plays a key role in release of Ca2+ from internal stores via inositol triphosphate mobilization. Western and Northern blot analyses revealed a greatly enhanced expression of mGluR5 in rats during early stages of hypothalamic development compared with the adult. This enhanced developmental expression provides an explanation for the dramatic physiological response of developing neurons to metabotropic glutamate receptor activation and supports the argument that metabotropic glutamate receptors may play an important role in hypothalamic development. During development, expression of the mGluR5 gene was reduced, not only in the hypothalamus but also in other regions of the brain. A differential decrease in mGluR5 protein was found in different brain regions with Western blot analysis. The hypothalamus showed a sixfold decrease in mGluR5 with development, whereas the cortex showed only a threefold decrease. Immunocytochemistry with an affinity-purified antibody against a peptide deduced from the cloned mGluR5 gene revealed selective expression in some regions in the adult hypothalamus. In the adult and developing (postnatal day 10) brain, immunoreactive neurons were found in the suprachiasmatic nucleus, preoptic area, lateral hypothalamus, and mammillary region, areas where the related metabotropic glutamate receptor mGluR1 is also found. In contrast, the ventromedial nucleus, an area critically involved in the regulation of food intake and metabolic balances, showed strong mGluR5 immunoreactivity but no mGluR1 immunoreactivity. Little or no mGluR5 staining was found in the neurosecretory neurons of the paraventricular, supraoptic, and arcuate nuclei. Ultrastructurally, mGluR5 was associated with the cytoplasmic face of the plasmalemma on hypothalamic dendrites, dendritic spines, and neuronal perikarya in the adult. The strongest immunoreactivity was found in patches on the membrane, sometimes associated with the postsynaptic side of synapses and sometimes associated with nonsynaptic dendritic or perikaryal membrane. Intense immunostaining was found on some astrocyte processes surrounding synaptic complexes containing asymmetrical synapses. These astrocytes would be in an ideal position to receive excitatory signals from glutamatergic axons. Unlike the punctate appearance of immunolabeling on neuronal membranes, astrocytes showed continuous staining along the plasma membrane.
代谢型谷氨酸受体mGluR5是一种G蛋白偶联受体，通过肌醇三磷酸动员在从内部储存中释放Ca2+方面发挥关键作用。蛋白质免疫印迹法（Western blot）和RNA印迹法（Northern blot）分析显示，与成年大鼠相比，在大鼠下丘脑发育早期mGluR5的表达大幅增强。这种发育过程中增强的表达为发育中的神经元对代谢型谷氨酸受体激活的显著生理反应提供了解释，并支持了代谢型谷氨酸受体可能在下丘脑发育中起重要作用的观点。在发育过程中，mGluR5基因的表达不仅在下丘脑中减少，在大脑的其他区域也减少。蛋白质免疫印迹分析发现在不同脑区mGluR5蛋白有差异地减少。随着发育，下丘脑的mGluR5减少了六倍，而皮质仅减少了三倍。用针对从克隆的mGluR5基因推导的肽段的亲和纯化抗体进行免疫细胞化学分析，揭示了在成年下丘脑的一些区域有选择性表达。在成年和发育中的（出生后第10天）大脑中，在视交叉上核、视前区、下丘脑外侧区和乳头体区域发现了免疫反应性神经元，这些区域也发现了相关的代谢型谷氨酸受体mGluR1。相反，腹内侧核，一个在食物摄入和代谢平衡调节中起关键作用的区域，显示出强烈的mGluR5免疫反应性，但没有mGluR1免疫反应性。在室旁核、视上核和弓状核的神经分泌神经元中几乎没有发现mGluR5染色。在超微结构上，在成年大鼠中，mGluR5与下丘脑树突、树突棘和神经元胞体的质膜胞质面相关。在膜上的斑块中发现最强的免疫反应性，有时与突触的突触后侧相关，有时与非突触性树突或胞体膜相关。在含有不对称突触的突触复合体周围的一些星形胶质细胞突起上发现强烈的免疫染色。这些星形胶质细胞处于接收来自谷氨酸能轴突的兴奋性信号的理想位置。与神经元膜上免疫标记的点状外观不同，星形胶质细胞沿着质膜显示连续染色。
