Moreover, we examined the status of microglial M1/M2 phenotypes and their respective secreted factors (neuroinflammatory cytokines and molecules of the BDNF signaling system), as well as subsequent hippocampal neurogenesis and synaptic plasticity, to elucidate the mechanisms of spatial learning and memory impairment induced by gut microbiota perturbation after chronic METH exposure. The gene discussed is BDNF; the disease is memory impairment.