The mammalian circadian clock located in the suprachiasmatic nucleus (SCN) produces robust daily rhythms including rest–wake. SCN neurons synthesize and respond to γ-aminobutyric acid (GABA), but its role remains unresolved. We tested the hypothesis that γ2- and δ-subunits of the GABA A receptor in the SCN differ in their regulation of synchrony among circadian cells. We used two approaches: 1) shRNA to knock-down (KD) the expression of either γ2 or δ subunits in the SCN or 2) knock-in mice harboring a point mutation in the M2 domains of the endogenous GABA A γ2 or δ subunits. KD of either γ2 or δ subunits in the SCN increased daytime running and reduced nocturnal running by reducing their circadian amplitude by a third. Similarly, δ subunit knock-in mice showed decreased circadian amplitude, increased duration of daily activity, and decreased total daily activity. Reduction, or mutation of either γ2 or δ subunits halved the synchrony among, and amplitude of, circadian SCN cells as measured by firing rate or expression of the PERIOD2 protein, in vitro. Surprisingly, overexpression of the γ2 subunit rescued these phenotypes following KD or mutation of the δ subunit, and overexpression of the δ subunit rescued deficiencies due to γ2 subunit KD or mutation. We conclude that γ2 and δ GABA A receptor subunits play similar roles in maintaining circadian synchrony in the SCN and amplitude of daily rest–wake rhythms, but that modulation of their relative densities can change the duration and amplitude of daily activities.

中文翻译：

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GABA A 受体亚基组成调节视交叉上核细胞之间静息-觉醒和同步的昼夜节律


位于视交叉上核 （SCN） 的哺乳动物生物钟产生强劲的日常节律，包括休息-觉醒。SCN 神经元合成并响应 γ-氨基丁酸 （GABA），但其作用仍未解决。我们检验了 SCN 中 GABA A 受体的 γ2 亚基和 δ 亚基在昼夜节律细胞间同步调节方面不同的假设。我们使用了两种方法：1） shRNA 敲低 （KD） SCN 中 γ2 或 δ 亚基的表达，或 2） 在内源性 GABA A γ2 或 δ 亚基的 M2 结构域中携带点突变的敲入小鼠。SCN 中 γ 2 或 δ 亚基的 KD 通过将其昼夜节律振幅降低三分之一来增加日间跑步并减少夜间跑步。同样，δ 亚基敲入小鼠表现出昼夜节律振幅降低，日常活动持续时间增加，每日总活动减少。γ2 或 δ 亚基的减少或突变使昼夜节律 SCN 细胞的同步性和振幅减半，通过在体外 PERIOD2 蛋白的放电速率或表达来测量。令人惊讶的是，γ2 亚基的过表达挽救了 KD 或 δ 亚基突变后的这些表型，而 δ 亚基的过表达挽救了由于 γ2 亚基 KD 或突变引起的缺陷。我们得出结论，γ2 和 δ GABA A 受体亚基在维持 SCN 中的昼夜节律同步和每日休息-觉醒节律的振幅方面起着相似的作用，但调节它们的相对密度可以改变日常活动的持续时间和振幅。