Differential regulation of neurotrophin S100B and BDNF in two rat models of depression.

Several clinical studies have demonstrated that serum brain-derived neurotrophic factor (BDNF) levels are decreased and serum S100B levels are increased in patients with major depression. In this study, we investigated whether these findings could be replicated in animal models of depression. We measured BDNF and S100B protein levels in the serum, prefrontal cortex, striatum and hippocampus of rats in models of depression, i.e., olfactory bulbectomy (OBX) and chronic unpredictable stress (CUS) models. Serum BDNF levels were significantly increased in the OBX rats, as were hippocampal BDNF levels in the CUS rats, in comparison with their respective controls. Significant increases in serum S100B levels were observed in both the OBX and CUS rats as compared with their respective controls; however, S100B levels were decreased in the prefrontal cortex of the CUS rats. No significant correlation was found between serum and regional brain S100B/BDNF levels. Our findings suggest that both of these animal models of depression, in which similar serum S100B level changes to those in depressed patients were observed, could be used as valid models to explore the role of S100B underlying major depression. Neither serum S100B nor BDNF levels reflect their levels in the brain, and changes in their levels in patients with neuropsychiatric diseases should be interpreted cautiously.