We recently discovered that the levels of growth factors in cerebrospinal fluid, such as Fgf17, impact oligodendrocyte growth and cognitive function. We are currently generating transgenic mice reporting the expression of Fgf17 and manipulating its levels to answer questions such as: which cells express Fgf17 in the adult and aging brain? Which cellular pathways regulate its secretion and how are they affected with age? What is the mode of action of Fgf17 signaling on oligodendrocytes and other neural cells?