Figure 1.
Precursor cell proliferation is affected differently in C57BL/6 and DBA/2 by short-term wheel running.
Proliferating cells in the subgranular zone were measured by incorporation of BrdU 12 h before experiment end (A). Data for single-housed mice showed no change in proliferating cell numbers after 4 days running in DBA/2 (B) but an increase in C57BL/6 (C). Proliferation correlated negatively with running wheel use in the DBA/2 animals (D), but positively for the C57BL/6 mice (E). Housing the DBA/2 mice in pairs also did not lead to a significant increase in proliferation after wheel running (F). Representative BrdU-stained sections are shown from C57BL/6 standard-housed (G) and running (H) animals. Bar graphs show mean ± SEM. All p-values are from two-tailed Student’s t-tests. Scale bars in G and H are 100 µm.
Figure 2.
Potential confounding factors.
DBA/2 mice did not run significantly different distances (A) or exhibit different running patterns. Typical actograms are shown for DBA/2 (B) and C57BL/6 (C) demonstrating that both strains, after a burst of activity as they are introduced to the new cage, run almost continuously throughout the hours of darkness (shaded regions). No significant effect of estrus cycle was observed in DBA/2 (D) or C57BL/6 (E) following one-way ANOVA. Serum corticosterone levels were reduced by running in DBA/2 (F) but not significantly in C57BL/6 (G). Bar graphs show mean ± SEM. All p-values are from two-tailed Student’s t-tests.
Figure 3.
Wheel running induces increased proliferation in DBA/2 animals after two weeks activity.
A scheme showing the labeling procedure with IdU (for acute proliferation; green symbol) and CldU (for survival; red symbol) used in this study (A). Cells in the subgranular zone proliferating 12 h before experiment end were measured by incorporation of IdU. Animals were housed under standard conditions (STD) or with a running wheel (RUN) for 4 weeks (B, C), 2 weeks (D) or 3 weeks (E). After 4 weeks, both DBA/2 (B), and C57BL/6 (C) mice showed a significant increase in precursor proliferation. DBA/2 animals exhibited a significant pro-proliferative response first after 2 weeks (D) and also 3 weeks (E) of wheel running. After 6 weeks of continued nightly wheel running, neither DBA/2 (F) nor C57BL/6 (G) showed a significant increase in proliferating cells in the subgranular zone. Bar graphs show mean ± SEM. All p-values are from two-tailed Student’s t-tests.
Figure 4.
The increase in new-born neuron number by wheel running is delayed in DBA/2 mice.
Animals were housed in STD or RUN cages for 4 weeks (A, B), 2 weeks (C), 3 weeks (D) or 6 weeks (E–G). Running mice of the strain C57BL/6 exhibited an increase in new neurons at both time points measured, 4 weeks (B) and 6 weeks (F). The number of new neurons in DBA/2 mice was only transiently increased after 3 weeks of running and not at 2 weeks (C), 4 weeks (A) or 6 weeks (E) following a single labeling injection. DBA/2 animals labeled with a series of injections over 10 days showed an increased number of new-born neurons after 6 weeks of wheel running (G). Representative fluorescence microscopy image of a new-born neuron stained using antibodies against CldU (H; green) and NeuN (I; magenta) with the arrow indicating a double-positive cell (J; merged image). Bar graphs show mean ± SEM. All p-values are from two-tailed Student’s t-tests. Scale bars in H–J are 20 µm.
Figure 5.
Summary of exercise-induced neurogenesis in DBA/2 over the time course studied.
Bars are the normalized difference of means for RUN vs. STD calculated as a ratio of the means. The transient peaks in running-induced proliferation (A), and new neuron number (B) can be clearly seen. Asterisks indicate a significant (p < 0.05) t-test from the raw values as presented in the text. Error bars are propagated SEM. See Methods for details.