Browsing by Author "Greer, Kisha"

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    Aberrant hippocampal neurogenesis contributes to learning and memory deficits in a mouse model of repetitive mild traumatic brain injury
    Greer, Kisha (Virginia Tech, 2019-10-02)
    Adult hippocampal neurogenesis, or the process of creating new neurons in the dentate gyrus (DG) of the hippocampus, underlies learning and memory capacity. This cognitive ability is essential for humans to operate in their everyday lives, but cognitive disruption can occur in response to traumatic insult such as brain injury. Previous findings in rodent models have characterized the effect of moderate traumatic brain injury (TBI) on neurogenesis and found learning and memory shortfalls correlated with limited neurogenic capacity. While there are no substantial changes after one mild TBI, research has yet to determine if neurogenesis contributes to the worsened cognitive outcomes of repetitive mild TBI. Here, we examined the effect of neurogenesis on cognitive decline following repetitive mild TBI by utilizing AraC to limit the neurogenic capacity of the DG. Utilizing a BrdU fate-labeling strategy, we found a significant increase in the number of immature neurons that correlate learning and memory impairment. These changes were attenuated in AraC-treated animals. We further identified endothelial cell (EC)-specific EphA4 receptor as a key mediator of aberrant neurogenesis. Taken together, we conclude that increased aberrant neurogenesis contributes to learning and memory deficits after repetitive mild TBI.
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    Abrogation of atypical neurogenesis and vascular-derived EphA4 prevents repeated mild TBI-induced learning and memory impairments
    Greer, Kisha; Gudenschwager-Basso, Erwin K.; Kelly, Colin; Cash, Alison; Kowalski, Elizabeth A.; Cerna, Steven; Ocampo, Collin Tanchanco; Wang, Xia; Theus, Michelle H. (2020-09-21)
    Brain injury resulting from repeated mild traumatic insult is associated with cognitive dysfunction and other chronic co-morbidities. The current study tested the effects of aberrant neurogenesis in a mouse model of repeated mild traumatic brain injury (rmTBI). Using Barnes Maze analysis, we found a significant reduction in spatial learning and memory at 24 days post-rmTBI compared to repeated sham (rSham) injury. Cell fate analysis showed a greater number of BrdU-labeled cells which co-expressed Prox-1 in the DG of rmTBI-injured mice which coincided with enhanced cFos expression for neuronal activity. We then selectively ablated dividing neural progenitor cells using a 7-day continuous infusion of Ara-C prior to rSham or rmTBI. This resulted in attenuation of cFos and BrdU-labeled cell changes and prevented associated learning and memory deficits. We further showed this phenotype was ameliorated in EphA4f.(/f)/Tie2-Cre knockout compared to EphA4f.(/f) wild type mice, which coincided with altered mRNA transcript levels of MCP-1, Cx43 and TGF beta. These findings demonstrate that cognitive decline is associated with an increased presence of immature neurons and gene expression changes in the DG following rmTBI. Our data also suggests that vascular EphA4-mediated neurogenic remodeling adversely affects learning and memory behavior in response to repeated insult.
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    Modulation of gap junction-associated Cx43 in neural stem/progenitor cells following traumatic brain injury
    Greer, Kisha; Chen, Jiang; Brickler, Thomas; Gourdie, Robert G.; Theus, Michelle H. (2017-09)
    Restoration of learning and memory deficits following traumatic brain injury (TBI) is attributed, in part, to enhanced neural stem/progenitor cell (NSPCs) function. Recent findings suggest gap junction (GJ)-associated connexin 43 (Cx43) plays a key role in the cell cycle regulation and function of NSPCs and is modulated following TBI. Here, we demonstrate that Cx43 is up-regulated in the dentate gyrus following TBI and is expressed on vimentin-positive cells in the subgranular zone. To test the role of Cx43 on NSPCs, we exposed primary cultures to the alpha-connexin Carboxyl Terminal (alpha CT1) peptide which selectively modulates GJ-associated Cx43. Treatment with alpha CT1 substantially reduced proliferation and increased caspase 3/7 expression on NSPCs in a dose-dependent manner. alpha CT1 exposure also reduced overall expression of Cx43 and phospho (p)-Serine368. These findings demonstrate that Cx43 positively regulates adult NPSCs; the modulation of which may influence changes in the dentate gyrus following TBI.