All sorts of things can trigger depression – genes, hormones, grief, certain diseases, and more. Inflammation has also been linked to the illness; people with rheumatoid arthritis are more likely to get it, and cancer patients given the pro-inflammatory drug interferon alpha often feel depressed as a result. Now, new research published in Nature Neuroscience suggests that inflammation could be the missing link between social stress and depression.
Many factors lead to social stress, especially if they affect your sense of worth like social anxiety, being bullied, and problems regarding body image. Unsurprisingly, these sorts of afflictions often have a worrying impact on a person’s mood, and now we think we know how.
A team of researchers, led by the Icahn School of Medicine at Mount Sinai, New York, looked at the physical effect of social stress on the brains of mice. They mixed 24 small inferior mice with bigger, dominant mice for 10 minutes a day for 10 days. Whilst some of the littler mice managed to deal with this, 14 became even timider and more socially withdrawn.
After the experiment, the team took blood, tissue, and DNA samples from the mice to analyze. They discovered that social stress can change mood via three steps.
Initially, the stress causes inflammation in the bloodstream. Then, it starts to become easier for inflammatory substances, like interleukin-6, to leak through the blood-brain barrier into the brain. Next, these substances disrupt the nucleus accumbens, a part of the brain that drives our reward circuit by controlling dopamine, which is involved in pleasure, and serotonin, which affects mood.
What’s more, mice that had become stressed in the presence of bullies were found to have genes that produced 40 percent less claudin-5, a protein that regulates the permeability of the blood-brain barrier, allowing more inflammatory substances to make their way into the brain.
While mice are a good model organism, they’re obviously different from people and can only tell us so much. Therefore, the researchers turned their attention to human brains. Comparing the post-mortem brain tissue of 39 people who had experienced depression and 24 people who hadn’t, they found claudin-5 levels in the nucleus accumbens to be around 50 percent lower in those who had suffered from depression when they were alive.
Consequently, a way to combat depression could be to tighten up the blood-brain barrier, so that unwanted inflammatory substances can’t get in. This, of course, is easier said than done.
Although issues with the blood-brain barrier aren’t the sole cause of depression, it’s still important to find out more about how its physical roots emerge in the brain, especially in a world where mental health is often ignored or stigmatized
[H/T: New Scientist]