BDNF and depressive disorder: MS may contribute to depression susceptibility in adulthood through alterations of the HPA axis in response to stress [18, 19], alterations in the expression of BDNF in different regions of the central nervous system (CNS) [20], alterations in the expression of serotonin in the CNS [21] and alterations in the expression of dopamine and its receptors [22] (Table 1).