BDNF and Alzheimer disease: Studies have shown that gp120 Tg mice display several features of AD, such as the accumulation of increased levels of proneurotrophin brain-derived neurotrophic factor in the hippocampus with decreased dendritic spines [128], impaired neurogenesis [129], impairment in sensory-motor gating [130], and cognitive deficits [131], thus suggesting that gp120 Tg mice are a suitable model for HAND in the context of AD.