Brain-derived neurotrophic factor (BDNF) is important for neurogenesis, differentiation and neuronal survival and is highly expressed in brain areas that are known to regulate cognitive and emotional behavior, such as hippocampus and amygdala (Strakowski et al., 2005). A body of evidence suggesting that BDNF is involved in BD. Cunha and colleagues showed that serum BDNF is decreased during manic and depressive episodes in BD patients, and that serum BDNF was negatively correlated with the severity of manic and depressive symptoms (Cunha et al., 2006). Also, the chronic administration of lithium (Frey et al., 2006a) or valproate increased BDNF expression in the hippocampus and temporal cortex in rat’s brain, suggesting that these mood stabilizers might produce a neurotrophic effect.