Shown are sample immunoreactive bands from Western blots. Lysates from the entire brain or the hippocampus of wild type and gp120 transgenic mice were subjected to Western blot analysis for brain-derived neurotrophic factor (BDNF, 15 kDa) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH, as an internal control, 35 kDa). The ratio of BDNF/GAPDH was quantified. Values represent mean ± SEM (n = 3 animals in each group; *p < 0.05; **p < 0.01; ***p < 0.001, one-way ANOVA followed by Duncan's test). A and B: BDNF expression was down-regulated in the entire brain and the hippocampus of gp120 transgenic mice. C and D: Hippocampal BDNF levels were increased in gp120 transgenic mice after running for 10 days. E: Hippocampal BDNF levels were increased by running for 10 or 20 days, but decreased by detraining in both wild type and gp120 transgenic mice. F: There was a positive correlation between the expression level of hippocampal BDNF and running distance.