Figure 1. Hippocampal neurogenesis in aged mice can be improved through direct or indirect stimulation of BDNF and IGF-1 pathways in vivo. BDNF and IGF-1 binds to the extracellular domains of their receptors, TrkB and IGF-1R respectively, which activate three major intracellular cascades of signaling pathways: PLCγ, ERK and PI3K. These pathways ultimately lead to the activation of CREB, a transcription factor mediating gene expression essential for neurogenesis. Other kinases involved in these pathways are not listed in the figure.