Inverse correlation of brain and blood BDNF levels in a genetic rat model of depression.

There is accumulating evidence that brain-derived neurotrophic factor (BDNF) plays a critical role in the pathophysiology of depression. Decreased serum levels have been reported in major depression, and a correlation between BDNF reduction and the severity of the disease was found. Moreover, in post-mortem hippocampal tissue, increased levels of BDNF immunoreactivity have been reported in subjects treated with antidepressants compared to untreated subjects. These findings indicate parallel changes in brain and serum BDNF levels during depression. BDNF has been measured in selected brain areas in several animal models. In investigations between Flinders Sensitive Line (FSL) and Flinders Resistant Line (FRL) rats, a genetic rat model of depression, no differences were found in BDNF levels in the frontal cortex and hippocampus, areas believed to be core brain regions in depression. However, to our knowledge brain and serum BDNF levels have never been reported in parallel for any psychiatric disease model. Therefore, we examined the levels of BDNF in whole blood, serum, cerebrospinal fluid (CSF), hippocampus, and frontal cortex in male FSL and FRL rats. BDNF levels in serum and whole blood of FSL rats were significantly increased compared to FRL rats. In contrast, in the hippocampus the BDNF level was significantly decreased in FSL compared to FRL rats while no differences were found in the frontal cortex and CSF. The differential regulation of the BDNF levels in hippocampus, serum, and whole blood in FSL/FRL rats adds to the hypothesis that neurotrophic factors are related to the pathophysiology of depression.

Differential brain, but not serum VEGF levels in a genetic rat model of depression.

Compared to the classical monoamine hypotheses focus on neuroplasticity is a major new approach in studies of depression and antidepressants. Recent studies have demonstrated that vascular endothelial growth factor (VEGF) is regulated by antidepressant treatment in rodents. However, in depressive patients no significant changes were found in the serum VEGF levels compared to control subjects. To our knowledge, brain and serum VEGF levels have never been reported in parallel for any psychiatric disease model. That prompted us to examine the levels of VEGF in serum, hippocampus, frontal cortex, corpus striatum, and hypothalamus in male Flinders Sensitive Line (FSL) and Flinders Resistant Line (FRL), a genetic rat model of depression. The VEGF levels were identical in the FSL and the FRL rats in serum, corpus striatum, and hypothalamus. In hippocampus and frontal cortex, the VEGF levels were significantly decreased in the FSL rats compared to the FRL rats. The results may add to the hypothesis that altered expression of growth factors/neurotrophic factors are related to the pathophysiology of depression.

Detection of brain-derived neurotrophic factor (BDNF) in rat blood and brain preparations using ELISA: pitfalls and solutions.

Quantification of endogenous brain-derived neurotrophic factor (BDNF) can be performed with an enzyme-linked immunosorbent assay (ELISA). Although BDNF has been determined in blood and brain preparations in numerous studies with ELISA kits, the methodological issues regarding measurements of BDNF concentrations in the blood and particularly in the brain have only been superficially investigated. We aimed at validating and optimizing the BDNF ELISA kit with respect to measurements in rat blood and brain samples. We found that the pre-analytical conditions were critical for plasma samples, but not serum or whole blood samples. The intra- and inter-assay variation and the accuracy and yield of the BDNF ELISA kit in rat serum and brain tissue were conducted with the optimal dilutions of frontal cortex and hippocampus extract. The optimal dilutions of frontal cortex and hippocampus extracts were determined to be 20 and 120 times, and we established that the intra-assay coefficient of variation (CV%) was 8 in hippocampus and 2 in frontal cortex and serum. The inter-assay variation was also low with a CV% of 11 or less in hippocampus, frontal cortex, and serum. Finally, we found that the accuracy and yield of the BDNF measurements were high in serum and low in hippocampus and frontal cortex. We conclude that the BDNF ELISA kit determines serum BDNF accurately and with high reproducibility. Furthermore it can be used for measurement of BDNF in rat brain preparations when particular precautions are taken and in particular with care regarding the dilution of the brain tissue samples.