BDNF and schizophrenia: A significant positive correlation was found between the serum level of BDNF and the serum level of 5-HT (r = 0.49, p = 0.0061, Figure 3) and the 5-HT/Trp value (r = 0.55, p = 0.0018, Figure 4) in the schizophrenia group (Table 4A).