Analysis for the cycle variation of [Cl^-]_i in supraoptic chiasma nucreus neuron

GABA是大脑中最主要的抑制性神经递质。然而，在昼夜节律的调节中，GABA显示出兴奋作用并发挥重要作用。在一个活的有机体中，生理和行为参数是由内源性振荡器控制的，并以大约24小时的周期显示出每日的节律性。振子的位置因物种而异。在哺乳动物中，视交叉上核（SCN）被广泛认为是振荡器的所在地。在视觉系统中，有报道称GABA对视网膜和视觉皮层的未成熟神经元表现出兴奋作用，从而诱导钙内流。因此，GABA在神经元发育过程中可能具有一定的营养作用。本研究采用6-甲氧基- n -乙基喹啉碘化（MEQ）荧光成像技术，比较了GABA对SCN、背外侧展状核（DLG）和视觉皮层（VC）神经元[Cl]_i变化的影响。此外，我们认为这些区域的神经元Cl^-稳态的差异调节过程。因此，我们检测了阳离子-Cl^-共转运蛋白的表达变化，如外向的K^+-Cl^-共转运蛋白KCC2和内向的Na^+、K^+-2Cl^-共转运蛋白NKCC1在SCN、DLG和VC中的表达变化。SCN神经元的[Cl]_i和NKCC1 mRNA的表达在白天高于夜间。抗利尿激素在白天有下调[Cl]_i的趋势。仅在未成熟VC中，GABA的应用引起了[Cl]_i的增加，表明[Cl]_i降低。在P0 DLQ中KCC2 mRNA的表达高于VC。这表明DLG神经元对Cl^-的挤压程度高于VC，因此DLG没有观察到gaba能兴奋效应，因为Cl^-的负平衡电位更大。

GABA is the most principal inhibitory neurotransmitter in the brain. However, in the regulation of circadian rhythm, it is suggested that GABA shows the excitatory effect and plays an important role. In a living organism, physiological and behavioral parameters are known to be controlled by endogenous oscillators and to show a daily rhysmicity with a period of about 24h. The seat of the oscillator differs from species to species. In mammals, the suprachiasmatic nucleus (SCN) is widely accepted as the seat of the oscillator. In the visual system, it has been reported that GABA shows the excitatory effects on immature neurons in the retina and the visual cortex, hence inducing calcium influx. Thus, GABA is expected to have some trophic action in the process of the neuronal development. In this study, using optical imaging of [Cl]_i with 6-methoxy-N-ethylquinolinium iodide (MEQ) fluorescence, we have compared the effects of GABA on neuronal [Cl]_i changes in the SCN, the dorsal lateral geniculate nucleus (DLG), and the visual cortex (VC). In addition, we consider that differential regulational process of neuronal Cl^-homeostasis in those regions. Therefore, we examined the expession changes of cation-Cl^-cotransporters, e.g., outwardly directed K^+-Cl^-cotransporter KCC2 and inwardly directed Na^+,K^+-2Cl^-cotransporter NKCC1, in SCN, DLG and VC. The [Cl]_i and expression of NKCC1 mRNA of SCN neurons was higher in daytime than in nighttime. The application of vasopressin tended to downregulate [Cl]_i in daytime. And only in the immature VC, application of GABA elicited an increase in, indicating a decrease in [Cl]_i. In the P0 DLQ the expression of KCC2 mRNA signals were higher than that in VC. This suggests that extrusion of Cl^-from neuron is higher in the DLG than in the VC, so that GABAergic excitatory effect were not observed in DLG because of more negative equilibrium potential for Cl^-.