BDNF and bipolar disorder: In a separate study, the expression of BDNF transcripts containing the 5′ exons I, IIc, IV, and VI (corresponding to BDNF splice variants 3, 2, 5, and 4, respectively) were assessed in the DLFPC, hippocampus and striatum of individuals diagnosed with bipolar disorder, major depressive illness and schizophrenia and controls (30).