Kuhlman Sandra J, Silver Rae, Le Sauter Joseph, Bult-Ito Abel, McMahon Douglas G
Department of Physiology, University of Kentucky, Lexington, Kentucky 40536-0084, USA.
J Neurosci. 2003 Feb 15;23(4):1441-50. doi: 10.1523/JNEUROSCI.23-04-01441.2003.
The endogenous circadian clock of the mammalian suprachiasmatic nucleus (SCN) can be reset by light to synchronize the biological clock of the brain with the external environment. This process involves induction of immediate-early genes such as the circadian clock gene Period1 (Per1) and results in a stable shift in the timing of behavioral and physiological rhythms on subsequent days. The mechanisms by which gene activation permanently alters the phase of clock neuron activity are unknown. To study the relationship between acute gene activation and persistent changes in the neurophysiology of SCN neurons, we recorded from SCN neurons marked with a dynamic green fluorescent protein (GFP) reporter of Per1 gene activity. Phase-resetting light pulses resulted in Per1 induction in a distinct subset of SCN neurons that also exhibited a persistent increase in action potential frequency 3-5 hr after a light pulse. By simultaneously quantifying Per1 gene activation and spike frequency in individual neurons, we found that the degree of Per1 induction was highly correlated with neuronal spike frequency on a cell-by-cell basis. Increased neuronal activity was mediated by membrane potential depolarization as a result of a reduction in outward potassium current. Double-label immunocytochemistry revealed that vasoactive intestinal peptide (VIP)-expressing cells, but not arginine vasopressin (AVP)-expressing cells, exhibited significant Per1 induction by light pulses. Rhythmic GFP expression occurred in both VIP and AVP neurons. Our results indicate that the steps that link acute molecular events to permanent changes in clock phase involve persistent suppression of potassium current, downstream of Per1 gene induction, in a specific subset of Per1-expressing neurons enriched for VIP.
哺乳动物视交叉上核（SCN）的内源性昼夜节律时钟可被光重置，以使大脑生物钟与外部环境同步。这一过程涉及诱导即刻早期基因，如昼夜节律时钟基因Period1（Per1），并导致后续几天行为和生理节律时间的稳定变化。基因激活永久性改变时钟神经元活动相位的机制尚不清楚。为了研究急性基因激活与SCN神经元神经生理学持续变化之间的关系，我们记录了用Per1基因活性的动态绿色荧光蛋白（GFP）报告基因标记的SCN神经元。相位重置光脉冲导致SCN神经元的一个独特子集中Per1的诱导，这些神经元在光脉冲后3 - 5小时也表现出动作电位频率的持续增加。通过同时量化单个神经元中Per1基因激活和动作电位频率，我们发现Per1诱导程度在逐个细胞基础上与神经元动作电位频率高度相关。神经元活动增加是由于外向钾电流减少导致膜电位去极化介导的。双标记免疫细胞化学显示，表达血管活性肠肽（VIP）的细胞，而非表达精氨酸加压素（AVP）的细胞，在光脉冲作用下表现出显著的Per1诱导。VIP和AVP神经元中均出现有节律的GFP表达。我们的结果表明，将急性分子事件与时钟相位永久变化联系起来的步骤涉及在富含VIP的Per1表达神经元的特定子集中，在Per1基因诱导下游对钾电流的持续抑制。
