BDNF and familial Alzheimer disease: AD, Alzheimer's disease; FMT, fecal microbiota transplantation; n, number; 5×FAD, 5× familial Alzheimer's disease; C57BL/6, C57 black mice; BDNF, brain-derived neurotrophic factor; TNF, tumor necrosis factor; IL, interleukin; WT, wild type; APPswe/PS1dE9, APP/PS1-21; MWM, Morris water maze test; ORT, object recognition test; PSD-95, postsynaptic density protein 95; COX2, cyclooxygenase 2; CD11b, integrin alpha M chain; SCFAs, short-chain fatty acids; ↑, increase; ↓, decrease.