BDNF and premenstrual tension: CNS inflammation can affect the regulation of the hypothalamic-pituitary-ovary axis (HPO), HPA axis (25), the serotonin (5-HT) system (26), the Gamma-aminobutyric acidergic (GABAergic) system (27) and brain-derived neurotrophic factor (BDNF) (7), all of which have long been associated with the risk of PMS/PMDD (20, 28–30).