Calcium imaging using GCaMP indicators and miniature microscopes has been used to image cellular populations during long timescales and in different task phases, as well as to determine neuronal circuit topology and organization. Because the hippocampus (HPC) is essential for tasks of memory, spatial navigation, and learning, calcium imaging of large populations of HPC neurons can provide new insight on cell changes over time during these tasks. All reported HPC in vivo calcium imaging experiments have been done in mouse. However, rats have many behavioral and physiological experimental advantages over mice. In this paper, we present the first (to our knowledge) in vivo calcium imaging from CA1 HPC in freely moving male rats. Using the UCLA Miniscope, we demonstrate that, in rat, hundreds of cells can be visualized and held across weeks. We show that calcium events in these cells are highly correlated with periods of movement, with few calcium events occurring during periods without movement. We additionally show that an extremely large percent of cells recorded during a navigational task are place cells (77.3 ± 5.0%, surpassing the percent seen during mouse calcium imaging), and that these cells enable accurate decoding of animal position and can be held over days with consistent place fields in a consistent spatial map. A detailed protocol is included, and implications of these advancements on in vivo imaging and place field literature are discussed.

SIGNIFICANCE STATEMENT In vivo calcium imaging in freely moving animals allows the visualization of cellular activity across days. In this paper, we present the first in vivo Ca2+ recording from CA1 hippocampus (HPC) in freely moving rats. We demonstrate that hundreds of cells can be visualized and held across weeks, and that calcium activity corresponds to periods of movement. We show that a high percentage (77.3 ± 5.0%) of imaged cells are place cells, and that these place cells enable accurate decoding and can be held stably over days with little change in field location. Because the HPC is essential for many tasks involving memory, navigation, and learning, imaging of large populations of HPC neurons can shed new insight on cellular activity changes and organization.

使用 GCaMP 指示器和微型显微镜的钙成像已用于在长时间尺度和不同任务阶段对细胞群进行成像，以及确定神经元回路拓扑和组织。由于海马 (HPC) 对于记忆、空间导航和学习任务至关重要，因此对大量 HPC 神经元进行钙成像可以提供有关这些任务期间细胞随时间变化的新见解。所有报道的 HPC体内钙成像实验都是在小鼠身上进行的。然而，与小鼠相比，大鼠具有许多行为和生理实验优势。在本文中，我们首次（据我们所知）在自由活动的雄性大鼠的 CA1 HPC 中进行体内钙成像。使用加州大学洛杉矶分校微型显微镜，我们证明，在大鼠中，数百个细胞可以被可视化并保持数周。我们发现这些细胞中的钙事件与运动周期高度相关，在不运动期间很少发生钙事件。我们还表明，在导航任务期间记录的细胞中有很大一部分是位置细胞（77.3 ± 5.0%，超过了小鼠钙成像期间看到的百分比），并且这些细胞能够准确解码动物位置，并且可以保持数天在一致的空间地图中具有一致的地点字段。其中包括详细的协议，并讨论了这些进展对体内成像和现场文献的影响。

意义声明自由活动的动物体内钙成像可以使细胞活动在几天内可视化。在本文中，我们首次展示了自由活动大鼠 CA1 海马 (HPC) 的体内Ca2+ 记录。我们证明数百个细胞可以被可视化并保持数周，并且钙活性与运动周期相对应。我们发现，成像细胞中很大一部分（77.3 ± 5.0%）是位置细胞，这些位置细胞能够实现准确解码，并且可以稳定保持数天，现场位置几乎没有变化。由于 HPC 对于涉及记忆、导航和学习的许多任务至关重要，因此对大量 HPC 神经元进行成像可以为细胞活动变化和组织提供新的见解。