The postnatal subventricular zone (SVZ) is a germinal center composed of neuronal precursors and glial fibrillary acidic protein positive (GFAP+) stem cells. The neuronal precursors proliferate and differentiate during their migration throughout the SVZ, along the rostral migratory stream (RMS) toward the olfactory bulb. The behavior of precursors is believed to be influenced by interactions with the progenitor environment, including local signals within the SVZ and surrounding cells. Thus, an understanding of the development of neuronal precursors in the SVZ requires an analysis of the signals that influence their behavior. Thus far, the signaling factors and their functions on SVZ progenitors remain largely unknown. However, we recently described the presence of GABA and functional GABAA receptors in postnatal SVZ neuronal progenitors, suggesting a signaling function of GABA in the SVZ. Furthermore, our recent data shows that GABA reduces the speed of neuronal progenitor migration. The goal of this proposal is to determine whether GABAergic signaling promotes the differentiation of neuronal progenitors in the postnatal subventricular zone.
Three aims will be addressed with immunocytochemistry, patch clamp recordings, Ca2+imaging, ELISA, immunohistochemistry, RT-PCR and gene microarray in acute, postnatal mouse slices and SVZ/RMS explants.
The first aim will test whether GABA promotes spontaneous Ca2+-dependent GABA release from neuronal progenitors and induces GABA receptor activation in surrounding neuronal progenitors. This positive feedback mechanism is hypothesized to stop when ambient GABA levels reach desensitizing levels that prevent GABAAR activation and reduce GABA release.
The second aim will determine whether GABA transporters are expressed in GFAP+ cells of the SVZ that form tubes filled with migrating neuronal progenitors. GFAP+ cells may thus create a microenvironment where ambient GABA levels are tightly regulated.
The third aim will examine whether ambient GABA promotes progenitor differentiation by stimulating BDNF synthesis in a Ca2+- and MAPK-dependent manner. The proposed experiments will provide important new information regarding the function of GABA in the SVZ. Data from these experiments will also considerably improve our understanding of the mechanisms of intercellular communication and cell differentiation in the SVZ, which is critical for the future therapeutic use of SVZ cells to replace damaged cells. ? ?
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