How exercise calms anxiety.

Another mouse story, as in the previous post, hopefully applicable to us humans. Gretchen Reynolds points to work of Gould and colleagues at Princeton showing that in the hippocampus of mice that have been in a running regime not only are new excitatory neurons and synapses generated, but also inhibitory neurons are more likely to become activated to dampen the excitatory neurons, in response to stress. This was a long term running response, because running mice were blocked from exercise for a day before stress testing in a cold bath that showed them to be less reactive to the cold than sedentary mice.

Physical exercise is known to reduce anxiety. The ventral hippocampus has been linked to anxiety regulation but the effects of running on this subregion of the hippocampus have been incompletely explored. Here, we investigated the effects of cold water stress on the hippocampus of sedentary and runner mice and found that while stress increases expression of the protein products of the immediate early genes c-fos and arc in new and mature granule neurons in sedentary mice, it has no such effect in runners. We further showed that running enhances local inhibitory mechanisms in the hippocampus, including increases in stress-induced activation of hippocampal interneurons, expression of vesicular GABA transporter (vGAT), and extracellular GABA release during cold water swim stress. Finally, blocking GABAA receptors in the ventral hippocampus, but not the dorsal hippocampus, with the antagonist bicuculline, reverses the anxiolytic effect of running. Together, these results suggest that running improves anxiety regulation by engaging local inhibitory mechanisms in the ventral hippocampus.