Circulating levels of GDNF in bipolar disorder.

Neurotrophic factors regulate the survival and growth of neurons, and influence synaptic efficiency and plasticity. Several studies suggest the existence of a relationship between changes in neurotrophic levels and bipolar disorder (BD). The glial cell-line derived neurotrophic factor (GDNF) influences monoaminergic neurons and glial cells, but its role in BD patients is controversial. In order to elucidate it we evaluated plasma levels of GDNF in a sample of 70 BD patients (35 in mania and 35 in euthymia) and compared with 50 healthy controls matched for age, gender and educational levels. GDNF plasma levels were measured by enzyme-linked immunosorbent assay (ELISA). Patients were assessed by a Mini-International Neuropsychiatric Interview (MINI-plus), Young Mania and Hamilton Depression Rating Scales. Plasma GDNF levels were significantly increased in BD patients in euthymia compared with BD patients in mania and healthy controls (p<0.05). GDNF plasma levels were correlated with age (ρ=0.30, p<0.05) and negatively correlated with manic symptoms in BD patients (ρ=-0.54, p<0.05). Our results provide evidence that peripheral levels of GDNF are related with different mood states in BD, reinforcing the involvement of neurotrophic factors in its physiopathology.