Cagampang F R, Rattray M, Powell J F, Chong N W, Campbell I C, Coen C W
Division of Biomedical Sciences, King's College London, UK.
Brain Res Mol Brain Res. 1996 Jan;35(1-2):190-6. doi: 10.1016/0169-328x(95)00203-5.
Using in situ hybridization, we examined temporal changes of the EAAC1 glutamate transporter mRNA within the suprachiasmatic nuclei (SCN) of rats in constant darkness. Film autoradiographs showed that the SCN and supraoptic nuclei (SON) contained a marked density of hybridization signal. Analysis of silver grains per cell in emulsion-dipped sections indicated that cellular expression of EAAC1 mRNA in the SCN was elevated during the latter part of the subjective night and at the beginning of the subjective day, with a peak at circadian time 23.1 as determined by cosinor analysis. The times at which EAAC1 mRNA is highest correspond to the time points at which extracellular glutamate, a neurotransmitter that putatively mediates photic entrainment, has been reported to be low within the SCN. The presence of EAAC1 mRNA in the SCN and SON may partially explain the resistance of these nuclei to glutamate receptor-mediated excitotoxins; furthermore, the raised level preceding subjective dawn in the SCN may ensure sub-toxic levels of extracellular glutamate at the onset of photic stimulation during the LD cycle. In contrast, cellular expression of EAAC1 mRNA in the cingulate cortex and reticular thalamus remained constant at all time points studied. These results suggest that there is circadian control of the EAAC1 mRNA by the clock intrinsic to the SCN.
我们利用原位杂交技术，研究了处于持续黑暗环境中的大鼠视交叉上核（SCN）内EAAC1谷氨酸转运体mRNA的时间变化。放射自显影片显示，SCN和视上核（SON）含有显著密度的杂交信号。对浸有乳胶的切片中每个细胞的银颗粒进行分析表明，SCN中EAAC1 mRNA的细胞表达在主观夜间后期和主观白天开始时升高，经余弦分析确定，在昼夜节律时间23.1时达到峰值。EAAC1 mRNA最高的时间点与据报道SCN内细胞外谷氨酸（一种据推测介导光同步化的神经递质）水平较低的时间点相对应。SCN和SON中存在EAAC1 mRNA可能部分解释了这些核团对谷氨酸受体介导的兴奋性毒素的抗性；此外，SCN中主观黎明前水平升高可能确保在明暗周期中光刺激开始时细胞外谷氨酸处于亚毒性水平。相比之下，在研究的所有时间点，扣带回皮质和丘脑网状核中EAAC1 mRNA的细胞表达保持恒定。这些结果表明，SCN内的生物钟对EAAC1 mRNA存在昼夜节律控制。
