BDNF and major depressive disorder: [91] This is of relevancy because both proBDNF and mature BDNF are active, showing opposing effects via the p75NTR and tropomyosin-related kinase B (TrkB) receptor, respectively, for example, as seen in studies that have identified a decrease in the production of mature BDNF and an increase in the levels of pro-peptide BDNF in the parietal cortex of MDD, schizophrenia and bipolar disorder groups in comparison with controls [92].