For a long time, the idea was that drugs that increased serotonin in the brain helped to relieve depressive symptoms, and so this must mean that depression was caused by low levels of serotonin in the brain (and this is still how you’ll see depression presented in a lot of antidepressant commercials). But it’s not that simple. Just because increasing something in the brain helps to fix a problem, it doesn’t mean that the problem is a LACK of that something. Headaches are not caused by lack of aspirin.
And decreasing serotonin doesn’t appear to CAUSE depression, though it can make you irritable. Not only that, some new drugs on the market such as Wellbutrin treat depression without touching serotonin levels. There’s no proof that people with depression have lower levels of serotonin than people without. So the serotonin theory is on the way out.
But the drugs still work (at least in a subset of patients). It turns out that these drugs which increase serotonin in the brain ALSO increase neurogenesis: the birth of new neurons. We used to think that we were born with all the neurons we would ever have, and that from birth on it was a smooth downward curve as we killed off our neurons with alcohol, head banging, and falling into things. But now we know that that isn’t true. In fact, your brain is capable of birthing new neurons and does so for most of your life.
And antidepressant drugs can INCREASE this rate of neuron birth, paprticularly in the hippocampus, and these increases produce antidepressant-like effects in animal models. Not only that, other things, like stress, can DECREASE hippocampal neuron birth rates. And this is where it begins to maybe come together. Because life stress is a major stimulus for depressive episodes in humans. Not only that, some patients with major depressive disorder show a dysregulation of the hypothalamic-pituitary axis, which controls stress responses. And if stress decreases hippocampal neurogenesis, and antidepressants increase neurogenesis…could it be that stress and hippocampal neurogenesis modulate each other and control depressive behavior?
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i'm the leftist liberal you've been warned about - the one who genuinely supports the expansion of the welfare state. i love politics and data and graffiti and street art and am far too lazy to use my shift key. if you need to reach me, you can email to abbyjean at the google email service.
