Details of how disruption of the gut microbiota may influence learning behaviour are presented in a mouse study published in Nature. Previous research has suggested a link between alterations in gut microbiota and modulated behaviours, but the underlying driving forces have been unclear. The new study identifies microbiota-derived signals that modify neuronal function and structure associated with fear responses.
David Artis and colleagues investigate the effect of microbiota manipulation on fear extinction learning in mice. Extinction learning is a process that occurs when an event associated with a cue changes, and behaviour is altered accordingly. In the present study, the authors trained mice to associate a noise with a small shock to the foot; this resulted in a fear response, in which the animals froze when they heard the tone. Once the shock was no longer delivered with the tone, control mice displayed reduced conditioned freezing, whereas germ-free or antibiotic-treated mice (that is, with depleted microbiota) continued to exhibit fear responses.
Depletion of microbiota was associated with changes in gene expression in nerve cells and defects in the learning-related changes to the neural architecture, Artis and colleagues report. They also identify four microbiota-derived compounds that are decreased in germ-free mice and have previously been linked to neuropsychiatric disorders. Together, these findings demonstrate the role of microbiota (and associated metabolites) in neuronal activity and behaviour.
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