Mick G, Yoshimura R, Ohno K, Kiyama H, Tohyama M
Unité 94, Institute National de la Santé de la Recherche Médicale, France.
Neuroscience. 1995 May;66(1):161-73. doi: 10.1016/0306-4522(95)00003-2.
Glutamate is the principal transmitter of retinal projections to the rodent suprachiasmatic nucleus, a circadian clock synchronized with the light-dark cycle through the activation of glutamate receptors of the ionotropic type. In vitro, an intracellular mobilization of calcium can be induced by glutamate within cells of the suprachiasmatic nucleus maintained in a calcium-free medium, suggesting a participation of metabotropic glutamate receptors coupled to phospholipase C. Using in situ hybridization histochemistry, we examined the expression of messenger RNAs encoding the mGluR1 and mGluR5 subtypes of metabotropic glutamate receptors in the suprachiasmatic nucleus of the adult rat and during postnatal development. In the adult, mGluR1 was expressed in a small subset of neurons segregated caudally within the ventrolateral subdivision of the nucleus, while mGluR5 was mainly expressed in ventrolateral neurons within the middle third of the nucleus. Both subtypes were expressed in morphologically similar small cells, but mGluR5 was also solely expressed in a small population of larger neurons located at the dorsalmost aspect of the ventrolateral subdivision. In addition, with mGluR1 probe silver grain clusters exhibiting a grain density close but below the significant level were observed throughout the ventrolateral subdivision of the nucleus. At birth, mGluR1 and mGluR5 were similarly expressed throughout the caudal half of the nucleus. The expression of mGluR1 increased during early postnatal development and exhibited an adult pattern at postnatal day 21. The expression of mGluR5 increased from postnatal day 7 and reached the adult pattern at postnatal day 45. These observations suggest that each subtype of metabotropic glutamate receptor coupled to phospholipase C underlies specific roles within the rat suprachiasmatic nucleus during postnatal development and in the adult. In the adult, ionotropic and metabotropic receptors likely co-expressed within neuronal subsets located in the retinal terminal field may have interactive and/or additive effects on intracellular calcium concentration. Metabotropic receptors may thus participate in the mediation of photic information conveyed to a subset of neurons. During postnatal development, metabotropic receptors may play a role in the maturation of glutamatergic synapses associated with the retinal input.
谷氨酸是视网膜向啮齿动物视交叉上核投射的主要神经递质，视交叉上核是一个昼夜节律时钟，通过激活离子型谷氨酸受体与明暗周期同步。在体外，在无钙培养基中培养的视交叉上核细胞内，谷氨酸可诱导细胞内钙的动员，这表明与磷脂酶C偶联的代谢型谷氨酸受体参与其中。我们使用原位杂交组织化学方法，检测了成年大鼠和出生后发育过程中视交叉上核中编码代谢型谷氨酸受体mGluR1和mGluR5亚型的信使核糖核酸的表达。在成年大鼠中，mGluR1在核腹外侧亚区尾侧分离的一小部分神经元中表达，而mGluR5主要在核中间三分之一的腹外侧神经元中表达。两种亚型均在形态相似的小细胞中表达，但mGluR5也单独表达于腹外侧亚区最背侧的一小群较大神经元中。此外，用mGluR1探针在整个核的腹外侧亚区观察到银粒簇，其颗粒密度接近但低于显著水平。出生时，mGluR1和mGluR5在核尾侧半部分的表达相似。mGluR1的表达在出生后早期发育过程中增加，并在出生后第21天呈现成年模式。mGluR5的表达从出生后第7天开始增加，并在出生后第45天达到成年模式。这些观察结果表明，与磷脂酶C偶联的代谢型谷氨酸受体的每种亚型在大鼠视交叉上核的出生后发育和成年期发挥特定作用。在成年大鼠中，位于视网膜终末场的神经元亚群内可能共表达的离子型和代谢型受体，可能对细胞内钙浓度产生相互作用和/或累加效应。因此，代谢型受体可能参与介导传递给一部分神经元的光信息。在出生后发育过程中，代谢型受体可能在与视网膜输入相关的谷氨酸能突触成熟中发挥作用。
