Voluntary running and environmental enrichment restores impaired hippocampal neurogenesis in a triple transgenic mouse model of Alzheimer's disease

Alzheimer's disease (AD) affects memory and neurogenesis. Adult neurogenesis plays an important role in memory function and impaired neurogenesis contributes to cognitive deficits associated with AD. Increased physical/cognitive activity is associated with both reduced risk of dementia and increased neurogenesis. Previous attempts to restore hippocampal neurogenesis in transgenic mice by voluntary running (RUN) and environmental enrichment (ENR) provided controversial results due to lack of non-transgenic (non-Tg) control and inclusion of social isolation as "standard" housing environment. Here, we determine the effect of RUN and ENR upon hippocampal neurogenesis in a triple transgenic (3xTg-AD) mouse model of AD, which mimics AD pathology in humans. We used single and double immunohistochemistry to determine the area density of hippocampal proliferating cells, measured by the presence of phosphorylated Histone H3 (HH3), and their potential neuronal and glial phenotype by co-localizing the proliferating cells with the immature neuronal marker doublecortin (DCX), mature neuronal marker (NeuN) and specific astroglial marker (GFAP). Our results show that 3xTg-AD mice in control environment exhibit impaired hippocampal neurogenesis compared to non-Tg animals at 9 months of age. Exposure to RUN and ENR housing restores hippocampal neurogenesis in 3xTg-AD animals to non-Tg control levels. Differentiation into neurones and glial cells is affected neither by transgenic status nor by housing environment. These results suggest that hippocampus of 3xTg-AD animals maintains the potential for cellular plasticity. Increase in physical activity and/or cognitive experience enhances neurogenesis and provides a potential for stimulation of cognitive function in AD.