Neurogenesis induces anxiety?

Voluntary wheel running in rodents is correlated with an upregulation of adult neurogenesis, as well as activation of the HPA axis. However, the findings on the effects of voluntary exercise on anxiety have been ambiguous, with some tests indicating no change, some indicating a decrease, and some indicating an increase, the latter of which may be contra to the presupposition that neurogenesis unilaterally decreases depression.

Fuss et al allowed mice 3 weeks of free access to a running wheel and measured the amount of usage during that time. When subjected to an open field test, running mice showed a decrease in distance moved and velocity of movement compared to controls, and they showed increased anxiety-like behavior in other tests like the O-maxe and dark-light box as well. Although cell differentiation in the hippocampus was significantly higher in the brains of running mice as opposed to controls (as measured by doublecortin), the overall number of cells in the dentate gyrus had no significant difference. Thus the authors suggest that instead of simply targeting increased neurogenesis in all anxiety cases it may be prudent to simply attempt to return it to basal levels.

Reference

Fuss et al. 2009 Voluntary exercise induces anxiety-like behavior in adult C57BL/6J mice correlating with hippocampal neurogenesis.