What chronic stress does to your brain
Lorianna De Giorgio, Toronto Star, July 15, 2011
What does chronic stress do to your brain?
Yale University researchers have found that chronic stress plays havoc on the brain by blocking out an important gene that protects the brain from depression.
Neuritin—“an activity-dependent gene that regulates neuronal plasticity” that is important for normal brain function, not just protection against depression—is decreased by chronic stress, Ronald Duman, a neurobiologist at Yale University and his team report in the study. “Neuritin produces antidepressant actions and blocks the neuronal and behavioural deficits caused by chronic stress,” they say in the June edition of the journal Proceedings of the National Academy of Sciences.
Neuritin is found in all humans and animals, and researchers focused on neuritin in the hippocampus part of the brain—the place where memory is formed.
Duman and his colleagues exposed lab rats to high levels of stress to see how their brains reacted. Stressors included food deprivation, mixing up their day-to-night schedules and isolation.
“They are relatively mild (stressors) individually but when you do them continuously over time it adds up to a fair amount of stress for the animal,” Duman says.
“One of the first things we found was that chronic stress exposure decreased the amounts of this protein called neuritin, which has been linked to (the growth) of neural processes.
“The question was whether or not changes in this protein contribute to … stress and also whether the increase that we saw with anti-depressant in that protein could account for the effect of the anti-depressant on both the neural processes as well as on behaviour.”
Duman and his team found that “over-expressing” the protein increased the number of synaptic connections and also produced behavioural effects that “would be similar to what we would observe with an anti-depressant,” he says. In some cases, the effects were superior to those with anti-depressants.
“Neuronal connections or synapses are the sites of contact that allow information to pass between neurons,” Duman explains.
Researchers found decreased levels of neuritin caused an atrophy of spinal connections and also produced depressive-like behaviours in the rats.
While past research has already shown that stress can lead to a retraction of neural processes or the atrophy (deterioration) of neuronal connections in the brain, little research had been done about the connection between neuritin and stress.
Duman has done post-mortem studies in the past on the brains of depressed patients, finding that there was also a decrease of neuritin.
Major depressive disorder affects up to 17 per cent of the U.S. population, with anti-depressants only effective for one-third of those suffering from the disorder, according to research published in Duman’s study.
Depression affects roughly 121 million people worldwide, according to the World Health Organization.
Duman hopes his study will shed further light on the connection between stress and depression.
Currently there are no anti-depressants on the market that contain neuritin.