BDNF and mood disorder: These observations include that pain and mood disorders modulate neuronal pathways involved in the same brain regions [6] and are associated with the imbalance of brain-derived neurotrophic factor (BDNF), neurotransmitter norepinephrine (NE, also known as noradrenaline, NA, and serotonin (5-hydroxytryptamine or 5-HT)) levels [7], and, in the central nervous system, alterations in serotonergic neurotransmission [8].