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The role of microglia and neuropeptides in regulating hippocampal neurogenesis.

Sivasathiaseelan H, Nunan R, Zaben M, Shtaya A, Gray WP (2009) The role of microglia and neuropeptides in regulating hippocampal neurogenesis. Neuroscience 2009 Abstracts 31.26/B52. Society for Neuroscience, Chicago, IL.

Summary: Adult mammalian neurogenesis is evident in the hippocampal dentate gyrus where it plays a role in learning and memory and is implicated in the pathophysiology of several brain disorders. Microglia, the innate immune cells of the brain, have recently emerged as an important component of the neurogenic niche, however their role in the regulation of neurogenesis under physiological and pathophysiological conditions is a matter of debate. The aim of this study is to investigate the effect of microglia on hippocampal neurogenesis and to look at how vasoactive intestinal peptide (VIP), a potent immunomodulatory neuropeptide found in dentate gyrus interneurons, modulates the effects microglia have on neurogenesis. In this study, we have investigated the effect of microglial depletion (using MAC-SAP), microglial co-culture and addition of microglia-conditioned-medium on primary hippocampal cell cultures derived from post-natal rats. We have also looked at how pre-treatment of microglia with VIP alters their effect on hippocampal cultures. Bromodeoxyuridine was used as a marker of cell proliferation. Quantification of cell death was achieved using the nuclear stain 4′,6-diamidino-2-phenylindole and Propidium Iodide. Immunohistochemistry was used to phenotype cells for nestin, GFAP and Tuj1. We have shown that microglial depletion results in a reduction in the numbers of nestin, GFAP and Tuj1 expressing cells. This reduction has been shown to be attributable to a decrease in cell survival and proliferation. Conversely, co-culture of microglia with hippocampal neurons or addition of their conditioned medium results in increased cell survival and proliferation. Pre-treatment of microglia with VIP was shown to increase both their proliferative and trophic effect on hippocampal cultures. In conclusion, this study demonstrates that microglia induce proliferative and trophic effects on neural stem cells and immature neurons through the release of soluble factors. Furthermore, we provide evidence that VIP regulates the release of these soluble factors, thus identifying a novel neuro-immuno-neurogenic link.

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