Department of Biomedical Engineering, Washington University, St. Louis, Missouri 63110.
Department of Medicine, Cardiovascular Division.
J Neurosci. 2023 Jul 12;43(28):5132-5141. doi: 10.1523/JNEUROSCI.0182-23.2023. Epub 2023 Jun 20.
Neurons in the suprachiasmatic nucleus (SCN) generate circadian changes in the rates of spontaneous action potential firing that regulate and synchronize daily rhythms in physiology and behavior. Considerable evidence suggests that daily rhythms in the repetitive firing rates (higher during the day than at night) of SCN neurons are mediated by changes in subthreshold potassium (K) conductance(s). An alternative "bicycle" model for circadian regulation of membrane excitability in clock neurons, however, suggests that an increase in NALCN-encoded sodium (Na) leak conductance underlies daytime increases in firing rates. The experiments reported here explored the role of Na leak currents in regulating daytime and nighttime repetitive firing rates in identified adult male and female mouse SCN neurons: vasoactive intestinal peptide-expressing (VIP), neuromedin S-expressing (NMS) and gastrin-releasing peptide-expressing (GRP) cells. Whole-cell recordings from VIP, NMS, and GRP neurons in acute SCN slices revealed that Na leak current amplitudes/densities are similar during the day and at night, but have a larger impact on membrane potentials in daytime neurons. Additional experiments, using an conditional knockout approach, demonstrated that NALCN-encoded Na currents selectively regulate daytime repetitive firing rates of adult SCN neurons. Dynamic clamp-mediated manipulation revealed that the effects of NALCN-encoded Na currents on the repetitive firing rates of SCN neurons depend on K current-driven changes in input resistances. Together, these findings demonstrate that NALCN-encoded Na leak channels contribute to regulating daily rhythms in the excitability of SCN neurons by a mechanism that depends on K current-mediated rhythmic changes in intrinsic membrane properties. Elucidating the ionic mechanisms responsible for generating daily rhythms in the rates of spontaneous action potential firing of neurons in the suprachiasmatic nucleus (SCN), the master circadian pacemaker in mammals, is an important step toward understanding how the molecular clock controls circadian rhythms in physiology and behavior. While numerous studies have focused on identifying subthreshold K channel(s) that mediate day-night changes in the firing rates of SCN neurons, a role for Na leak currents has also been suggested. The results of the experiments presented here demonstrate that NALCN-encoded Na leak currents differentially modulate daily rhythms in the daytime/nighttime repetitive firing rates of SCN neurons as a consequence of rhythmic changes in subthreshold K currents.
视交叉上核（SCN）中的神经元会产生自发性动作电位放电率的昼夜变化，从而调节和同步生理和行为的日常节律。大量证据表明，SCN 神经元重复放电率（白天高于夜间）的昼夜节律是由亚阈值钾（K）电导变化介导的。然而，时钟神经元膜兴奋性的昼夜调节的另一种“自行车”模型表明，NALCN 编码的钠（Na）渗漏电导的增加是白天放电率增加的基础。这里报道的实验探讨了 Na 渗漏电流在调节成年雄性和雌性小鼠 SCN 神经元的日间和夜间重复放电率中的作用：血管活性肠肽表达（VIP）、神经调节素 S 表达（NMS）和胃泌素释放肽表达（GRP）细胞。急性 SCN 切片中 VIP、NMS 和 GRP 神经元的全细胞记录显示，Na 渗漏电流幅度/密度在白天和夜间相似，但对白天神经元的膜电位影响更大。使用条件性敲除方法的额外实验表明，NALCN 编码的 Na 电流选择性调节成年 SCN 神经元的日间重复放电率。动态钳位介导的操作表明，NALCN 编码的 Na 电流对 SCN 神经元重复放电率的影响取决于 K 电流驱动的输入电阻变化。总之，这些发现表明，NALCN 编码的 Na 渗漏通道通过一种依赖于 K 电流介导的内在膜特性节律变化的机制，有助于调节 SCN 神经元兴奋性的日常节律。阐明负责产生视交叉上核（SCN）神经元自发性动作电位放电率的昼夜节律的离子机制，是理解分子钟如何控制生理和行为中的昼夜节律的重要步骤。虽然许多研究都集中在确定介导 SCN 神经元昼夜放电率变化的亚阈值 K 通道上，但也有人提出了 Na 渗漏电流的作用。这里提出的实验结果表明，NALCN 编码的 Na 渗漏电流通过亚阈值 K 电流的节律变化，差异调节 SCN 神经元的日间/夜间重复放电率的昼夜节律。
