Department of Anatomy and Neurobiology, University of California, Irvine, CA 92697, USA.
Proc Natl Acad Sci U S A. 2012 Oct 2;109(40):E2726-34. doi: 10.1073/pnas.1210929109. Epub 2012 Sep 10.
Endogenous brain rhythms occurring at various frequencies and associated with distinct behavioral states provide multiscale temporal windows that enable cells to time their spiking activity with high precision, which is thought to be important for the coding of information in neuronal circuits. However, although the selective timing of GABAergic inputs to specific spatial domains of principal cells are known to play key roles in network oscillations, the in vivo firing patterns of distinct hippocampal interneurons in awake animals are not known. Here we used a combination of juxtacellular labeling techniques with recordings from anesthesia-free, head-fixed mice running or resting on a spherical treadmill to study the oscillation-dependent discharges by two major interneuronal subtypes, the perisomatically projecting parvalbumin-positive basket cells (PVBCs) and distal dendritically projecting oriens lacunosum moleculare (OLM) cells. Recordings of the spiking activity of post hoc-identified CA1 interneurons during theta (5-10 Hz), gamma (25-90Hz), epsilon ("high-gamma"; 90-130 Hz), and ripple (130-200 Hz) oscillations revealed both cell type- and behavioral state-dependent entrainments of PVBC and OLM cell discharges in awake mice. Our results in awake mice differed in several respects from previous data on interneuronal discharge patterns in anesthetized animals. In addition, our results demonstrate a form of frequency-invariant, cell type-specific temporal ordering of inhibitory inputs in which PVBC-derived perisomatic inhibition is followed by OLM cell-generated distal dendritic inhibition during each of the network oscillation bands studied, spanning more than an order of magnitude in frequencies.
内源性脑节律以各种频率发生，并与不同的行为状态相关联，提供了多尺度的时间窗口，使细胞能够以高精度调整其尖峰活动的时间，这被认为对于神经元回路中的信息编码很重要。然而，尽管已知 GABA 能输入到主细胞的特定空间域的选择性定时在网络振荡中起着关键作用，但在清醒动物中不同海马中间神经元的在体放电模式尚不清楚。在这里，我们使用细胞外标记技术与无麻醉、头部固定的小鼠在球形跑步机上跑步或休息时的记录相结合，研究了两种主要中间神经元亚型（PVBC 和 OLM 细胞）的振荡依赖性放电。在 theta（5-10 Hz）、gamma（25-90 Hz）、epsilon（“高 gamma”；90-130 Hz）和 ripple（130-200 Hz）振荡期间，对事后鉴定的 CA1 中间神经元的尖峰活动进行记录，揭示了在清醒小鼠中，PVBC 和 OLM 细胞放电的细胞类型和行为状态依赖性同步。我们在清醒小鼠中的结果在几个方面与麻醉动物中中间神经元放电模式的先前数据不同。此外，我们的结果表明，在研究的每个网络振荡带中，PVBC 衍生的胞体抑制紧随 OLM 细胞产生的远端树突抑制，存在一种频率不变的、细胞类型特异性的抑制输入时间顺序，其跨越了一个多数量级的频率。
