Biology / Health / Medicine / Science

Brain juice

Today I’ve been asked about norepinephrine, by someone who is taking an SNRI, or serotonin-norepinephrine reuptake inhibitor.

So, norepinephrine is also known as noradrenaline. It’s a hormone and a neurotransmitter, so it plays a role all through the body, including in the brain. It’s easier to ask what it doesn’t do, at a casual look: it’s involved in releasing glucose from fat stores, immune system activation and deactivation, digestion… I could go on! The point is that it’s a very important hormone for the body. In the brain (which is the most interesting part here), it’s closely involved with alertness and readiness to act.

So how does an SNRI work? Some people assume that taking an antidepressant is like taking a little pill of serotonin, but it’s really not as simple as that. Our understanding of depression is that increased serotonin helps the brain to function properly, alleviating the low moods and other symptoms of depression, and norepinephrine is targeted for more or less the same reasons. We can’t just have swallow serotonin and norepinephrine, though. That would just get destroyed by our digestive system, or absorbed in the gut and probably used there! It’s unlikely that you’d see much effect from just swallowing serotonin pills.

What SSRIs and SNRIs do instead is prevent neurons from mopping up the neurotransmitters after firing. Normally, the neuron will release the neurotransmitter into the synapse, but then it will gather it all back up. SSRIs and SNRIs increase the amount of serotonin and norepinephrine at the synapse not by creating more, but by preventing the neuron from taking it back up. This helps neurons function more smoothly, passing messages through your brain that can get lost without the neurotransmitters being freely available — and your body will just compensate by making more serotonin to use. (And the SSRI/SNRI will block it from being picked back up…)

That’s a very basic explanation, of course, and it way oversimplifies things. In many cases, even scientists don’t fully understand what our own bodies are doing, and the treatment of many mental disorders is a guess in the dark. When we’re lucky, it’s a good guess.

By the way, if you’re wondering why medication is such an individual thing — why doesn’t Prozac work for everyone, if it’s so good?! — it’s all down to body chemistry. There are so many different body chemistries, as many as there are people. Maybe some people’s digestive system won’t take up the medication in significant enough quantities, or maybe we’re making the wrong guess about what they need. Maybe they just don’t respond to that particular drug. That’s why it’s important to have different antidepressants available — and to be willing to try different ones! Some people strike lucky first time, but until we understand the brain better and until we can individualise medicine to a much greater degree, luck is still required.

Let nobody tell you we know all there is to know about biology! We definitely do not, and that’s why it remains just as exciting as any other branch of science.

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