Analysis of the hippocampal neural network activity <i>in vivo</i> by miniature fluorescence microscopy in neurological pathologies

Abstract

Miniature fluorescent microscopy is a method that enables neurobiologists to visualize and record neuronal activity of a specific brain region in vivo in freely moving mice [1]. The use of miniscope presents a novel approach for acquiring extensive data on the structure, function, and organization of the neuronal network in the region of interest at the in vivo level [2, 3]. In this way, the use of miniscope could also identify changes caused by pathological conditions, such as seizures, neurodegenerative diseases, and neurological complications resulting from past viral infections, like influenza virus. Data obtained through miniature fluorescent microscopy contains information on the functioning properties and original connections of hundreds of simultaneously recorded neurons. Our group developed an open-source toolbox to move from qualitative to quantitative analysis of recorded data, providing neurobiologists with statistical metrics from miniscope processed recordings through “Minian” [4]. Neuronal network state was defined in open-field test conditions under normal circumstances using a self-developed toolbox in the current study. In this study, 5-month-old wild B6SJL mice were injected with AAV-GCaMP6f virus in the hippocampus. After 3 weeks, a gradient lens was implanted over the hippocampus with baseplate fixation. Changes in calcium levels were measured using Miniscope v3 in the “open field” test. A software package was created for quantitative analysis of the neuron activity data. As a result, the study concluded that the most consistent data over the course of five days were the Pearson correlation coefficient for the active spike method (based on binary results from active phase segmentation) and the network degree level (the ratio of interconnected neurons depending on the presence of a connection). These measures displayed a high level of stability throughout the recordings. Furthermore, the PCA method applied to the calculated statistics indicated a close relationship between the coordinates that described the activity of the hippocampal neuronal network during the five-day testing period. The miniscope technique appears to be an effective tool for identifying shifts in neuronal networks during the progression of neurodegenerative diseases, such as Alzheimer’s disease [5]. It may also aid in detecting possible changes following neurological complications related to viral infections.