Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts, USA.
Department of Neuroscience, Peter O'Donnell Jr. Brain Institute, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
J Comp Neurol. 2024 Jun;532(6):e25624. doi: 10.1002/cne.25624.
The hypothalamic suprachiasmatic nucleus (SCN) is the central pacemaker for mammalian circadian rhythms. As such, this ensemble of cell-autonomous neuronal oscillators with divergent periods must maintain coordinated oscillations. To investigate ultrastructural features enabling such synchronization, 805 coronal ultrathin sections of mouse SCN tissue were imaged with electron microscopy and aligned into a volumetric stack, from which selected neurons within the SCN core were reconstructed in silico. We found that clustered SCN core neurons were physically connected to each other via multiple large soma-to-soma plate-like contacts. In some cases, a sliver of a glial process was interleaved. These contacts were large, covering on average ∼21% of apposing neuronal somata. It is possible that contacts may be the electrophysiological substrate for synchronization between SCN neurons. Such plate-like contacts may explain why the synchronization of SCN neurons is maintained even when chemical synaptic transmission or electrical synaptic transmission via gap junctions is blocked. Such ephaptic contact-mediated synchronization among nearby neurons may therefore contribute to the wave-like oscillations of circadian core clock genes and calcium signals observed in the SCN.
下丘脑视交叉上核（SCN）是哺乳动物昼夜节律的中央起搏器。作为这样一个具有不同周期的自主神经元振荡器的集合体，必须保持协调的振荡。为了研究实现这种同步的超微结构特征，用电子显微镜对 805 张小鼠 SCN 组织的冠状超薄切片进行成像，并将其排列成体积堆栈，从中选择 SCN 核心内的选定神经元进行计算机重建。我们发现，簇状 SCN 核心神经元通过多个大型体-体板状接触彼此物理连接。在某些情况下，一个神经胶质过程的薄片被交错。这些接触很大，平均覆盖约 21%的相邻神经元体。这些接触可能是 SCN 神经元之间同步的电生理基础。这种板状接触可能解释了为什么即使阻断化学突触传递或通过缝隙连接的电突触传递，SCN 神经元的同步仍然得以维持。因此，这种附近神经元之间的电突触接触介导的同步可能有助于 SCN 中观察到的生物钟核心基因和钙信号的波浪状振荡。
