How exercise calms anxiety.

In my scans of journals' tables of contents I missed this interesting piece by Schoenfeld et al., which is pointed to by a summary in the New York Times "Well" section. Running is known to stimulate the production of more dendritic spines, the primary sites of excitatory synapses, on excitatory neurons throughout the hippocampal circuitry known to be involved in emotion processing. In spite of producing more excitable nerve tissue, exercise also calms anxiety (in mice and in humans). Schoenfeld suggest that this is because another effect of exercise is to increase the levels of proteins that process the inhibitory neurotransmitter GABA in local inhibitory nerve cells. Their results suggest that running improves anxiety regulation by engaging local inhibitory mechanisms in the ventral hippocampus. (By the way, GABA is a popular dietary supplement for supposedly calming social anxiety.) Here is their more technical abstract:

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.