Cellular Electrophysiology of the Suprachiasmatic Nuclei

描述（由申请人提供）：哺乳动物大脑中的视交叉上核（SCN）包含主生物钟。单个SCN神经元是称职的昼夜节律振荡器，并构成一个稳定和增强昼夜节律定时信号产生的神经网络。3-氨基丁酸（3-Aminobutyric acid， GABA）可以改变生物钟的相位，抑制光引起的相移，同步SCN背侧和腹侧神经元的活动，调节单个SCN神经元的动作电位放电频率。我们研究的长期目标是了解gaba介导的神经传递在昼夜节律信号产生中的作用。gaba能神经传递的强度和功能后果受细胞内Cl-浓度的调节。在成人大脑中，GABAA受体的激活在白天抑制大多数SCN神经元，而在夜间，大多数GABAA反应是兴奋性的。GABAA受体介导的突触活性的昼夜差异源于昼夜周期中细胞内Cl-浓度的动态调节。负责增加细胞内Cl-的氯化钠-钾（NKCC1）共转运体和减少细胞内Cl-的氯化钾（KCC）共转运体家族在整个SCN中异质表达。我们假设GABA神经传递的昼夜变化取决于单个SCN神经元中表达的共转运体的类型和活性。本应用程序的目的是确定生物钟调节SCN中gaba介导的信号强度和极性的机制，以及这在调节SCN神经回路中所起的作用。我们将结合电生理和成像技术来确定NKCC1和KCC家族共转运蛋白在介导SCN中gaba能传递的强度和多样性中的作用。该提案的具体目的是：1)确定，在单个SCN神经元中，GABA激活的氯离子电流的方向是否在昼夜周期中GABA反应从抑制性到兴奋性的转变中起基础作用。2)研究NKCC1和KCC共转运蛋白在调节SCN神经网络活性中的作用。3)在表型鉴定的SCN神经元中，研究NKCC1共转运蛋白在决定抑制性和兴奋性GABAA受体介导电流平衡中的作用。4)研究由KCC共转运体调节的Cl-外排在GABAA受体介导的突触传递的大小和极性中的作用。

DESCRIPTION (provided by applicant): The suprachiasmatic nucleus (SCN) in the mammalian brain contains the master circadian clock. Individual SCN neurons are competent circadian oscillators and constitute a neural network that stabilizes and enhances the generation of circadian timing signals. 3-Aminobutyric acid (GABA) shifts the phase of the circadian clock, inhibits light-induced phase shifts, synchronizes the activity of dorsal and ventral SCN neurons, and modulates the action potential firing frequency of individual SCN neurons. The long-term goal of our research is to understand the role of GABA-mediated neurotransmission in the generation of circadian timing signals. The strength and functional consequences of GABAergic neurotransmission are regulated by the intracellular Cl- concentration. In the adult brain, activation of GABAA receptors inhibits a majority of SCN neurons during the day, while at night the majority of GABAA responses are excitatory. The day-night difference in GABAA receptor-mediated synaptic activity results from dynamic regulation of the intracellular Cl- concentration during the circadian cycle. The sodium-potassium-chloride (NKCC1) cotransporter responsible for increasing intracellular Cl- and the potassium-chloride (KCC) family of cotransporters that reduce intracellular Cl- are heterogeneously expressed throughout the SCN. We hypothesize that the circadian variation in GABA neurotransmission depends on the type and activity of the cotransporters expressed in individual SCN neurons. The goal of this application is to identify the mechanisms by which the circadian clock regulates the strength and polarity of GABA-mediated signaling in the SCN and the role this plays in regulating the SCN neural circuit. We will use a combination of electrophysiological and imaging techniques to determine the role of NKCC1 and the KCC family of cotransporters in mediating the magnitude and diversity of GABAergic transmission in the SCN. The Specific Aims of the proposal are: 1) Determine, in individual SCN neurons, whether the direction of the GABA-activated chloride current underlies the shift in GABA response from inhibitory to excitatory during a circadian cycle. 2) Investigate the role of the NKCC1 and KCC cotransporters in regulating the activity of the SCN neural network. 3) Examine the contribution of the NKCC1 cotransporter in determining the balance between inhibitory and excitatory GABAA receptor- mediated currents in phenotypically identified SCN neurons. 4) Examine the role of Cl- efflux as regulated by KCC cotransporters in modulating the magnitude and polarity of GABAA receptor-mediated synaptic transmission.