P021, a neurogenic neurotrophic compound which activates BDNF signaling, was found to cause an increase in neurogenesis, synaptic plasticity and a reduction in the hyperphosphorylation of tau via the tropomyosin-related kinase B (TrkB)/phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)-GSK3-β pathway in aged Fisher rats and 3xTg-AD mice [47,67,68,69]. The gene discussed is BDNF; the disease is Alzheimer disease.