BDNF and depressive disorder: In preclinical research, Li et al. reported that mice with spatial restraint stress-induced depression exhibited antidepressant-like behavioral effects 1 h after bilateral BoNT/A facial injection that continued for at least 7 days, together with increased serotonin and brain-derived neurotrophic factor (BDNF) levels and activation of the BDNF–ERK–CREB pathway in the hippocampus [17].