This 2015 Italian rodent study found:

“There is a window of plasticity that allows familiar and novel experiences to alter anxiety– and depressive-like behaviors, reflected also in electrophysiological changes in the dentate gyrus (DG).

A consistent biomarker of mood-related behaviors in DG is reduced type 2 metabotropic glutamate (mGlu2), which regulates the release of glutamate. Within this window, familiar stress rapidly and epigenetically up-regulates mGlu2..and improves mood behaviors.

These hippocampal responses reveal a window of epigenetic plasticity that may be useful for treatment of disorders in which glutamatergic transmission is dysregulated.”

The current study included two of the authors of A common dietary supplement that has rapid and lasting antidepressant effects.

The supplementary material showed the:

“Light–dark test as a screening method allowed identification of clusters of animals with a different baseline anxiety profile”

for the BDNF Val66Met subjects. This research methodology better handled the individual differences that often confound studies.

The study’s press release provided further details such as:

“Here again, in experiments relevant to humans, we saw the same window of plasticity, with the same up-then-down fluctuations in mGlu2 and P300 in the hippocampus, Nasca says. This result suggests we can take advantage of these windows of plasticity through treatments, including the next generation of drugs, such as acetyl-L-carnitine, that target mGlu2—not to ‘roll back the clock’ but rather to change the trajectory of such brain plasticity toward more positive directions.”

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I disagree with the authoring researchers’ extrapolation of these rodent findings to humans, which seemed to favor chemical intervention. Causes of human stress should be removed or otherwise addressed.

I hope that the study’s “familiar stress” findings won’t be use to attempt to justify potentially harmful practices such as Critical Incident Stress Debriefing, which mandatorily guides people to process recent trauma. Instead, An interview with Dr. Rachel Yehuda on biological and conscious responses to stress made a point about “windows of plasticity” that’s relevant to who we are as feeling human beings:

“What I hear from trauma survivors — what I’m always struck with is how upsetting it is when other people don’t help, or don’t acknowledge, or respond very poorly to needs or distress.”

http://www.pnas.org/content/112/48/14960.full “Stress dynamically regulates behavior and glutamatergic gene expression in hippocampus by opening a window of epigenetic plasticity”