In vitro quantitative RT-PCR of BDNF mRNA expression of umbilical cord mesenchymal stem cells (UC MSCs). A significant decrease in mRNA levels of BDNF was observed in the high-passaged UC MSCs compared to low-passaged UC MSCs. (Note: † significant from high-passage UC MSCs; TTF are control cDNA isolated from mice tail-tip fibroblasts.) Bar graph represents mean value; error bars represents SEM. BDNF, brain-derived neurotrophic factor; SEM, standard error of the mean.