In 2050, the population aged 65 and over will be almost double the number in 2012, increasing the importance of late life cognitive health and resilience. Adult hippocampal neurogenesis (AHN) is crucial for memory functions and recovery from stress in rodents. Little is known about human AHN in healthy aging and Alzheimer’s Disease (AD), less is known about age and AD effects on synaptic plasticity and brain circuits. In aging rodents and non- human primates, adult-generated neural cells tend to favor differentiation into glia instead of neurons, but phylogenetic differences dictate human studies. AHN studies require rigorous methods for visualization of AHN markers and data interpretation. These include assuring brain tissue quality, standardized tissue processing, use of brain toxicology and neuropathology, and strict clinical inclusion/exclusion criteria based on adequate clinical data. We and others have confirmed persistent AHN with aging in subjects without AD, but we found age- associated declines in angiogenesis and neuroplasticity as defined by expression of polysialiated cell adhesion molecule (PSA-NCAM) in fewer cells of the dentate gyrus (DG), which could reflect changes at the dendrite, spine or synaptic level, because PSA-NCAM is expressed with dendrite remodeling, neuron migration, and long term potentiation. Our preliminary data show that Kruppel Like Factor 9 (Klf9), a transcription factor necessary for neurogenesis-dependent synaptic plasticity and neuronal differentiation, declines with normal aging in human DG. We reported that the age-related angiogenesis decline is directly proportional to fewer cells expressing PSA- NCAM. Angiogenesis and AHN are regulated by vascular endothelial growth factor receptor 2 (VEGFR2), and we have pilot data showing fewer intra- and extra-vascular DG cells expressing VEGFR2 in older people. Studies of AHN in AD have shown conflicting findings of increased, no change, and deficits of AHN correlating with cognitive decline. We propose new techniques that have never been applied to study AHN, dendrite, spine, synaptic and vascular plasticity in normal human aging or AD brain tissue. To understand what sustains AHN and synaptogenesis, we will examine their relationship to expression of molecular regulators (Klf9 and VEGFR2). The sample will include hippocampi from the Brain Banks of NIMH and the New York AD Research Center: 80 without neuropsychiatric illness, neuropathology or psychotropic drug use, age 14-90, and 20 with AD, age 65- 90. Aims: 1. To study the neuronal or glial phenotype of doublecortin (DCX)-positive cells and quantify AHN and gliogenesis across the human lifespan. 2. To study age-associated changes in dendrite, spine and synapses and their molecular regulator Klf9 in CA1, CA3 and DG: 2a. Golgi-stained dendrite and spines; 2b. Number and length of neurofilament-immunoreactive dendrites; 2c. Pre/post-synaptic and dendritic protein expression: SYN1, PSD95 and spinophilin; 2d. Klf9 mR...