BDNF and infection: In case of injury or infection, microglia can switch to an activated and phagocytic state, defined by morphological changes, proliferation, increased production of neurotrophic [e.g., brain-derived neurotrophic factor (BDNF)] or inflammatory factors [e.g., tumor necrosis factor-α (TNF-α)], and enhanced oxidative stress [e.g., reactive oxygen species (ROS) production] (Fellner et al.,2011; Nimmerjahn et al.,2005).