Nature Neuroscience pp 519 - 525

Mice subjected to stress caused by the presence of an aggressive intruder, repress the gene that produces a growth factor called brain derived neurotrophic factor (BDNF), reports a paper in the April issue of Nature Neuroscience. This finding suggests a molecular pathway by which stress may cause lasting changes in gene regulation.

Eric Nestler and colleagues have previously reported that such socially stressed mice show a form of depression that mimics the human condition, and that treatment with antidepressants can improve their behavior. The team now uses this model to study gene changes that take place when mice are exposed to chronic defeat stress and when they are treated with antidepressants. These changes last for over a month after the social stress ends and are mediated by an increase in histone methylation - which usually represses gene expression - at the Bdnf promoter sites, leading to more stable repression of the gene. Treatment with the antidepressant imipramine increased histone acetylation - which usually promotes gene expression - by repressing an enzyme that deacetylates histones, thus reversing the effect on the Bdnf promoter.

If similar changes occur in humans, which are yet to be demonstrated, this work may lead to new therapeutic targets for stress-induced depression.

Nature Neuroscience pp 526 - 533

Many people struggle to maintain a regular exercise schedule on their own, but do better when they exercise with friends. In rats, exercising in groups is better for the brain as well, reports a study in the April issue of Nature Neuroscience.

Elizabeth Gould and colleagues study the effects of running on the generation of new neurons (neurogenesis) in the brains of adult rats housed in groups and in isolation. The authors report that running increases neurogenesis only when rats were housed in groups. However, in rats that run in social isolation, neurogenesis is suppressed. Running caused similar elevations of the stress hormone corticosterone in isolated or group-housed rats, but only animals that ran alone were vulnerable to the negative influence of corticosterone on neurogenesis. Moreover, individually housed runners showed higher levels of corticosterone in response to additional stress when compared to group-housed runners. Preventing the elevation in corticosterone levels in individually housed runners stimulated neurogenesis.

These results suggest that without social interaction, a normally beneficial experience can have negative effects on the brain.