Mechanisms of GABAergic Signaling in the Suprachiasmatic Nucleus Network

摘要 相当多的美国人的工作时间不同于传统的作息时间，并遭受着 打乱了昼夜节律计时系统。哺乳动物的主生物钟，位于视交叉上 细胞核(SCN)始终维持着位于组织中的生物钟之间的适当的相位关系 并将昼夜节律系统带入环境。SCN由单个神经元组成 振荡器通过细胞间通信耦合到神经网络中，从而产生健壮和精确的 节奏。我们研究的长期目标是了解耦合的细胞间信号机制 将SCN神经元转化为产生昼夜节律的神经网络。GABA能神经传递是一种 SCN神经网络的基本成分与突触后强度和极性的改变 GABA的反应改变了SCN的活性，最终改变了昼夜节律。GABA作为一种 均衡条件下的去同步信号和同步信号时的SCN神经网络 已经被环境光改变了。GABA作用于突触GABA(A)受体介导快速信号传递 在SCN神经元和突触外GABA(A)受体之间激活紧张性GABA(A)电流，该电流 调节单个SCN神经元的活动，并将网络活动的水平传达给相邻的 突触。我们推测，两个膜转运蛋白家族在细胞周期调控中起关键作用。 脊髓核内GABA神经传递的昼夜节律活动。GABA转运蛋白GAT-1和GAT-3的调节 神经递质GABA在突触外间隙的数量和时程与强直的大小 电流。在SCN中，GABA转运体只在星形胶质细胞中表达，这表明星形胶质细胞在 在调节GABA在SCN网络中的生理作用方面至关重要，但还没有确定的作用。在 成年SCN，GABA既是抑制性神经递质，也是兴奋性神经递质，尽管生理上 GABA神经传递的这种极性变化的意义尚不清楚。氯化物 钠-氯化钾(NKCC)和氯化钾(KCC)家族的共转运蛋白控制着 细胞内氯离子浓度和GABA(A)受体介导的电流的极性和幅度。我们 提出生物钟使用细胞内第二信使系统WNK-Spak激酶、钙离子- 激活的激酶和环状AMP激活的激酶来调节氯离子转运体的活性。的目标是 这一应用是为了更好地理解GABA能信号的调节机制，以及GABA是如何- 介导的信号转导有助于在SCN中产生昼夜节律定时信号。要做到这一点 目标，我们将使用单细胞电生理和成像技术与转基因小鼠一起 研究已识别的SCN神经元中GABA能神经传递的模型。增强了对 由GABA介导的细胞间信号机制将增强我们操纵生物钟的能力 并减少基于昼夜节律紊乱的患者所经历的症状。

Summary A significant number of Americans work non-traditional schedules and suffer the adverse health effects of a disrupted circadian timing system. The master mammalian circadian clock, located in the suprachiasmatic nucleus (SCN) maintains the proper phase relationship between circadian clocks located in tissues throughout the body and entrains the circadian system to the environment. The SCN is composed of individual neuronal oscillators coupled by intercellular communication into a neural network that generates a robust and precise rhythm. The long-term goal of our research is to understand the intercellular signaling mechanisms that couple SCN neurons into a neural network that generates circadian rhythms. GABAergic neurotransmission is a fundamental component of the SCN neural network and changing the strength and polarity of postsynaptic GABA responses modifies the activity of the SCN, and ultimately circadian rhythmicity. GABA serves as a desynchronizing signal under equilibrium conditions and a synchronizing signal when the SCN neural network has been modified by environmental light. GABA acts on synaptic GABA(A) receptors to mediate fast signaling between SCN neurons and on extrasynaptic GABA(A) receptors to activate a tonic GABA(A) current that modulates the activity of individual SCN neurons and communicates the level of network activity to adjacent synapses. We hypothesize that two membrane transporter families play critical roles in the regulation of the circadian activity of GABA neurotransmission in the SCN. The GABA transporters GAT-1 and GAT-3 regulate the amount and duration of neurotransmitter GABA in the extrasynaptic space and the magnitude of the tonic current. In the SCN, the GABA transporters are only expressed in astrocytes suggesting that astrocytes play a vital, but as of yet undetermined role in regulating the physiological actions of GABA in the SCN network. In the adult SCN, GABA serves as both an inhibitory and excitatory neurotransmitter although the physiological significance of this change in the polarity of GABA neurotransmission remains unknown. The chloride cotransporters of the sodium-potassium-chloride (NKCC) and potassium-chloride (KCC) families control the intracellular Cl- concentration and the polarity and magnitude of the GABA(A) receptor-mediated currents. We propose that the circadian clock uses the intracellular second messenger systems WNK-SPAK kinases, Ca2+- activated kinases, and cyclic AMP-activated kinases to regulate the activity of the Cl- transporters. The goal of this application is to understand better the mechanisms regulating GABAergic signaling and how GABA- mediated signaling contributes to the generation of circadian timing signals in the SCN. To accomplish this goal, we will use single cell electrophysiological and imaging techniques together with transgenic mouse models to study GABAergic neurotransmission in identified SCN neurons. Enhanced knowledge of the intercellular signaling mechanisms mediated by GABA will increase our ability to manipulate the circadian clock and reduce the symptoms experienced by patients with circadian-based disorders.