Centre de Recherche en Neurobiologie et Neurophysiologie de Marseille (CRN2M), CNRS-UMR 6231, Université de la Méditerranée, Faculté de Médecine Nord, Marseille, France.
Eur J Neurosci. 2010 Jan;31(2):359-70. doi: 10.1111/j.1460-9568.2009.07071.x. Epub 2010 Jan 13.
The daily temporal organization of rhythmic functions in mammals, which requires synchronization of the circadian clock to the 24-h light-dark cycle, is believed to involve adjustments of the mutual phasing of the cellular oscillators that comprise the time-keeper within the suprachiasmatic nucleus of the hypothalamus (SCN). Following from a previous study showing that the SCN undergoes day/night rearrangements of its neuronal-glial network that may be crucial for intercellular phasing, we investigated the contribution of glutamatergic synapses, known to play major roles in SCN functioning, to such rhythmic plastic events. Neither expression levels of the vesicular glutamate transporters nor numbers of glutamatergic terminals showed nycthemeral variations in the SCN. However, using quantitative imaging after combined immunolabelling, the density of synapses on neurons expressing vasoactive intestinal peptide, known as targets of the retinal input, increased during the day and both glutamatergic and non-glutamatergic synapses contributed to the increase (+36%). This was not the case for synapses made on vasopressin-containing neurons, the other major source of SCN efferents in the non-retinorecipient region. Together with electron microscope observations showing no differences in the morphometric features of glutamatergic terminals during the day and night, these data show that the light synchronization process in the SCN involves a selective remodelling of synapses at sites of photic integration. They provide a further illustration of how the adult brain may rapidly and reversibly adapt its synaptic architecture to functional needs.
哺乳动物的节律功能的日常时间组织，要求生物钟与 24 小时光暗周期同步，这被认为涉及到组成下丘脑视交叉上核（SCN）时间keeper 的细胞振荡器的相互相位调整。基于先前的一项研究表明，SCN 经历了昼夜神经元-神经胶质网络的重新排列，这可能对细胞间的相位至关重要，我们研究了谷氨酸能突触的贡献，已知谷氨酸能突触在 SCN 功能中发挥主要作用。在 SCN 中，囊泡谷氨酸转运体的表达水平或谷氨酸能末梢的数量均未显示出昼夜节律变化。然而，通过联合免疫标记后的定量成像，表达血管活性肠肽（已知是视网膜输入的靶标）的神经元上的突触密度在白天增加，谷氨酸能和非谷氨酸能突触都有助于增加（增加 36%）。对于在非视网膜接受区域中 SCN 传出的另一个主要来源——含有加压素的神经元上的突触则并非如此。与显示白天和夜间谷氨酸能末梢的形态特征没有差异的电子显微镜观察结果一起，这些数据表明 SCN 中的光同步过程涉及到光整合部位突触的选择性重塑。它们进一步说明了成年大脑如何快速和可逆地适应其突触结构以满足功能需求。
