Nucleotide release from glial cells plays important autocrine and paracrine signaling roles in the CNS and PNS. Recent studies suggest that the non-lytic release of ATP from glial cells can either involve regulated exocytosis or efflux through nucleotide-permeable channels. Extracellular ATP acting on plasmalemmal ionotropic P2X and metabotropic P2Y receptors modulates neuronal activity, induces calcium transients in astrocytes and generates critical intracellular second messengers implicated for instance in the development of gliosis following brain trauma and in the proliferation and migration of neural stem cells. Recently, we have obtained evidence that neural progenitor cells display spontaneous calcium oscillations that are highly dependent on activation of P2Rs. Bath application of purinergic receptor antagonists or of the ATP degrading enzyme apyrase prevented the occurrence of spontaneous calcium fluctuations. Moreover, blockade of P2Rs reduced the proliferation and the migration rates of these progenitors. These results suggest that neural progenitors have the ability to release ATP, which then plays a crucial autocrine, paracrine signaling role during early CNS development. Although identification of pathways involved on transmitter release from glial cells have been suggested for mature astrocytes, nothing is known about the developmental aspects of the mechanism(s) by which ATP is released from precursors. Therefore, the goal of this grant application is to evaluate whether and at which stage of astrocyte development three of the putative pathways for transmitter release are functionally competent (exocytosis/secretion and diffusion through ionotropic P2XRs and connexin hemichannels) and to determine their contribution to calcium oscillations and cell migration. Immunocytochemical, biochemical and pharmacological approaches combined with luminescence and fluorescence imaging will be used to identify ATP release pathways. This identification is fundamental for the understanding of the signaling mechanisms ongoing during CNS development and repair. ? ? ?
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