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Neurogenesis, Magnetic resonance imaging, Voxel-based morphometry, exercise, hippocampus, histology
Abstract:
Growing evidence indicates that physical exercise increases hippocampal
volume. This has consistently been shown in mice and men using magnetic
resonance imaging. On the other hand, histological studies have reported
profound alterations on a cellular level including increased adult
hippocampal neurogenesis after exercise. A combined investigation of
both phenomena has not been documented so far although a causal role of
adult neurogenesis for increased hippocampal volume has been suggested
before. We investigated 20 voluntary wheel running and 20 sedentary mice
after a period of 2 month voluntary wheel running. Half of each group
received focalized hippocampal irradiation to inhibit neurogenesis prior
to wheel running. Structural MRI and histological investigations
concerning newborn neurons (DCX), glial cells (GFAP), microglia,
proliferating and pyknotic cells, neuronal activation, as well as blood
vessel density and arborisation were performed. In a regression model,
neurogenesis was the marker best explaining hippocampal gray matter
volume. Individual analyses showed a positive correlation of gray matter
volume with DCX-positive newborn neurons in the subgroups, too.
GFAP-positive cells significantly interacted with gray matter volume
with a positive correlation in sham-irradiated mice and no correlation
in irradiated mice. Although neurogenesis appears to be an important
marker of higher hippocampal gray matter volume, a monocausal
relationship was not indicated, requesting further investigations.
