Brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) have essential roles in synaptic plasticity which is involved in pathogenesis and treatment of psychiatric disorders. However, it is not clear whether they act simultaneously during illness states in major psychiatric disorders.

BDNF and GDNF serum levels were measured concomitantly by enzyme-linked immunosorbent assay (ELISA) method in 171 patients diagnosed with schizophrenia (n = 33), bipolar disorder-manic episode (n = 39), bipolar/unipolar depression (n = 64, 24/40) and obsessive-compulsive disorder (n = 35) according to DSM-IV, and 78 healthy volunteers. SCID-I and SCID non-patient version were used for clinical evaluation of the patients and healthy volunteers, respectively. Correlations between the two trophic factor levels, and illness severity scores, duration of illness and medication dosages were studied across different illnesses.

While patients had equally lower BDNF levels in all diagnoses, GDNF levels were significantly higher in mania and lower in schizophrenia compared to healthy controls. BDNF levels were negatively correlated to illness severity scores in affective episodes (mania and depression). Longer duration of illness (> 5 years) had an impact on lower GDNF levels in schizophrenia. BDNF levels and antipsychotic drug dosages in schizophrenia, and GDNF levels and antidepressant drug dosages in obsessive-compulsive disorder were positively correlated.

Our data confirmed the evidence of equally deficient neuronal support by BDNF in all major psychiatric illnesses, but suggested a diverse glial functioning between schizophrenia and mania.