BDNF and migraine disorder: Intratracheal neomycin alters pulmonary microbiota, activating the vagus nerve via lung brain‐derived neurotrophic factor/tropomyosin receptor kinase B (BDNF/TrkB) pathway, further projecting to nucleus of solitary tract (NTS), then dorsal raphe nucleus (DRN), where activated serotoninergic neurons increase brain serotonin, alleviating migraine.