Department of Neurology, Geisel School of Medicine at Dartmouth Lebanon, NH, USA ; Program in Experimental and Molecular Medicine, Geisel School of Medicine at Dartmouth Lebanon, NH, USA.
Department of Physiology and Pharmacology, State University of New York, Downstate Medical Center Brooklyn, NY, USA ; The Robert F. Furchgott Center for Neural and Behavioral Science, State University of New York, Downstate Medical Center Brooklyn, NY, USA.
Front Neural Circuits. 2013 Nov 18;7:181. doi: 10.3389/fncir.2013.00181. eCollection 2013.
While extracellular somatic action potentials from freely moving rats have been well characterized, axonal activity has not. We report direct extracellular tetrode recordings of putative axons whose principal feature is a short duration waveform (SDW) with an average peak-trough length less than 179 μs. While SDW recordings using tetrodes have previously been treated as questionable or classified as cells, we hypothesize that they are representative of axonal activity. These waveforms have significantly shorter duration than somatic action potentials, are triphasic and are therefore similar to classic descriptions of microelectrode recordings in white matter and of in vitro action potential propagation along axons. We describe SDWs recorded from pure white-matter tracts including the alveus and corpus callosum. Recordings of several SDWs in the alveus exhibit grid-like firing patterns suggesting these axons carry spatial information from entorhinal cortical neurons. Finally, we locally injected the GABAA agonist Muscimol into layer CA1 of the hippocampus while simultaneously recording somatic activity and SDWs on the same tetrodes. The persistent activity of SDWs during Muscimol inactivation of somatic action potentials indicates that SDWs are representative of action potential propagation along axons projecting from more distal somata. This characterization is important as it illustrates the dangers of exclusively using spike duration as the sole determinant of unit type, particularly in the case of interneurons whose peak-trough times overlap with SDWs. It may also allow future studies to explore how axonal projections from disparate brain regions integrate spatial information in the hippocampus, and provide a basis for studying the effects of pharmaceutical agents on signal transmission in axons, and ultimately to aid in defining the potential role of axons in cognition.
虽然已经很好地描述了来自自由移动的大鼠的细胞外躯体动作电位，但轴突活动尚未得到描述。我们报告了直接细胞外四极管记录的假定轴突，其主要特征是具有短持续时间波形 (SDW) 的活动，平均峰谷长度小于 179 μs。虽然以前使用四极管记录的 SDW 被视为可疑或归类为细胞，但我们假设它们代表轴突活动。这些波形的持续时间明显短于躯体动作电位，是三相的，因此与经典描述的白质中的微电极记录和体外沿轴突传播的动作电位相似。我们描述了从纯白质束（包括齿状回和胼胝体）中记录的 SDW。在齿状回中记录的几个 SDW 表现出网格状发射模式，表明这些轴突携带来自内嗅皮质神经元的空间信息。最后，我们在海马体 CA1 层局部注射 GABA A 激动剂 Muscimol 的同时，在相同的四极管上记录躯体活动和 SDW。在 Muscimol 使躯体动作电位失活期间持续的 SDW 活动表明，SDW 代表从更远端的胞体沿轴突传播的动作电位。这种特征很重要，因为它说明了仅使用脉冲持续时间作为单元类型的唯一决定因素的危险，特别是在峰谷时间与 SDW 重叠的中间神经元的情况下。它还可能允许未来的研究探索来自不同脑区的轴突投射如何在海马体中整合空间信息，并为研究药物对轴突中信号传输的影响提供基础，并最终有助于确定轴突在认知中的潜在作用。
