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While it has been known that physical activity can improve cognitive function and protect against neurodegeneration, the underlying mechanisms for these protective effects are yet to be fully elucidated. There is a large body of evidence indicating that physical exercise improves neurogenesis and maintenance of neurons. Yet, its possible effects on glial cells remain poorly understood. Here, we tested whether physical exercise in mice alters the expression of trophic factor-related genes and the status of astrocytes in the dentate gyrus of the hippocampus. In addition to a significant increase in Bdnf mRNA and protein levels, we found that 4 weeks of treadmill and running wheel exercise in mice, led to (1) a significant increase in synaptic load in the dentate gyrus, (2) alterations in astrocytic morphology, and (3) orientation of astrocytic projections towards dentate granule cells. Importantly, these changes were possibly linked to increased TrkB receptor levels in astrocytes. Our study suggests that astrocytes actively respond and could indeed mediate the positive effects of physical exercise on the central nervous system and potentially counter degenerative processes during aging and neurodegenerative disorders.

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It has been suggested that increased GABAergic innervation in the hippocampus plays a significant role in cognitive dysfunction in Down syndrome (DS). Bolstering this notion, are studies linking hyper-innervation of the dentate gyrus (DG) by GABAergic terminals to failure in LTP induction in the Ts65Dn mouse model of DS. Here, we used extensive morphometrical methods to assess the status of GABAergic interneurons in the DG of young and old Ts65Dn mice and their 2N controls. We detected an age-dependent increase in GABAergic innervation of dentate granule cells (DGCs) in Ts65Dn mice. The primary source of GABAergic terminals to DGCs somata is basket cells (BCs). For this reason, we assessed the status of these cells and found a significant increase in the number of BCs in Ts65Dn mice compared with controls. Then we aimed to identify the gene/s whose overexpression could be linked to increased number of BCs in Ts65Dn and found that deleting the third copy of App gene in Ts65Dn mice led to normalization of the number of BCs in these mice. Our data suggest that App overexpression plays a major role in the pathophysiology of GABAergic hyperinnervation of the DG in Ts65Dn mice. © 2016 Wiley Periodicals, Inc.

Hippocampal structural and functional alterations in Alzheimer's disease (AD), detected by advanced imaging methods, have been linked to significant abnormalities in multiple internal and external networks in this critical brain region. Uncovering the temporal and anatomical pattern of these network alterations would provide important clues into understanding the pathophysiology of AD and suggest new therapeutic strategies for this multi-system and prevalent disorder. Over the last decade, we have focused on studying brain structures that provide major projections to the hippocampus (HC) and the pattern of de-afferentation of this area in mouse models of AD and a related neurodegenerative disorder, i.e. Down syndrome (DS). Our studies have revealed that major inputs into the hippocampal structure undergo significant age-dependent alterations. Studying locus coeruleus (LC), the sole source of noradrenergic terminals for the HC, it has been shown that these neurons show significant age-dependent degeneration in both mouse models of DS and AD. Furthermore, increasing noradrenergic signaling was able to restore cognitive function by improving synaptic plasticity, and possibly promoting microglia recruitment, and amyloid β (Aβ) clearance in transgenic (tg) mouse models of AD. Here, we re-examine the effects of alterations in major inputs to the hippocampal region and their structural and functional consequences in mouse models of neurodegenerative disorders. We will conclude that improving the function of major hippocampal inputs could lead to a significant improvement in cognitive function in both AD and DS.