Increased hippocampal fissure width is a sensitive indicator of rat hippocampal atrophy

Volume loss within the hippocampus is known as the most replicated finding of structural brain imaging studies of neuropsychiatric diseases. Although voxel-based auto or semi-auto volumetric measurements are widely used in the determination of the human hippocampus, the detection of hippocampal atrophy in rats is still a dilemma as it relies on a relatively primitive and complex approach. In this study, we aimed to develop a convenient way to measure the atrophy of the hippocampus in rats. Twenty-four male Wistar rats were exposed to chronic unpredictable mild stress (CUMS) and a wheel running test (WRT) to simulate the conditions of hippocampal volume atrophy and improvement. The hippocampal volume and hippocampal fissure (HiF) width were dynamically measured using 7 T structural magnetic resonance imaging (MRI) with the grayscale method at week 0, 2, 4, and 8. The changes in the hippocampal volume and HiF width in rats were compared. In addition, hematoxylin-eosin (HE) staining of the HiF was used to verify the MRI findings. The hippocampal volume and the HiF width presented opposite trends based on the MRI findings and the histology data. The atrophy of the hippocampal subfields was closely related to the corresponding increase in the HiF width. Determination of the HiF width may serve as a sensitive and convenient indicator of rat hippocampal atrophy.