BDNF and Cognitive impairment: Total abdominal irradiation (TAI) caused cognitive impairment in mouse models and upregulated miR-34a-5p expression in the small intestine and peripheral blood, which downregulated the expression of brain-derived neurotrophic factor in the hippocampus. Intravenous injections of miR-34a-5p antagomiR in the tail inhibited the increase of miR-34a-5p level in the peripheral blood and hippocampus and recovered the cognitive dysfunction.