Cellular Electrophysiology of the Suprachiasmatic Nuclei

描述(申请人提供)：哺乳动物大脑中的视交叉上核(SCN)含有主生物钟。单个SCN神经元是有能力的昼夜节律振荡器，并构成一个神经网络，稳定和增强昼夜节律信号的产生。3-氨基丁酸(GABA)可使昼夜节律发生移位，抑制光诱导的相移，使背侧和腹侧SCN神经元的活动同步，并调节单个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氯离子浓度的调节。在成人大脑中，GABAA受体的激活在白天抑制大多数SCN神经元，而在晚上大多数GABAA反应是兴奋性的。GABAA受体介导的突触活动的昼夜差异是昼夜节律中细胞内氯离子浓度动态调节的结果。负责增加细胞内氯离子含量的钠-钾转运体(NKCC1)和减少细胞内氯离子含量的氯化钾(KCC)共转运体家族在整个SCN中异质性表达。我们假设GABA神经传递的昼夜变化依赖于单个SCN神经元中表达的辅转运体的类型和活性。这项应用的目的是确定生物钟调节SCN中GABA介导的信号的强度和极性的机制，以及这种机制在调节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家族在调节SCN中GABA能传递的大小和多样性中的作用。该提案的具体目的是：1)确定在单个SCN神经元中，GABA激活的氯电流的方向是否在昼夜周期中支持GABA反应从抑制到兴奋的转变。2)研究NKCC1和KCC共转运蛋白在调节SCN神经网络活动中的作用。3)研究NKCC1共转运体在确定表型识别的SCN神经元抑制性和兴奋性GABAA受体介导的电流之间的平衡中的作用。4)研究受KCC共转运体调控的氯离子外流在调节GABAA受体介导的突触传递的幅度和极性中的作用。

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.