This topic contains 4 replies, has 3 voices, and was last updated by Mel Mel 1 year ago.

Neurotransmitter and SSRI Questions

  • Dust

    Hey Kati,
    This is kind of a long bunch of technical/sciency kinds of questions. I know you’re not a psychiatrist or a neurologist or an MD of any kind, but maybe you’ll be able to help answer, or maybe you’ll know someone who can. The psychiatrist I see is… unhelpful in this matter. And neurologists are hard to come by, apparently. I’m not really sure where else to ask.

    Part 1:
    So, axons release neurotransmitters. Some activate nearby dendrites, some are reabsorbed/re-uptaken by the neuron that released them, and some are “lost”.
    The molecules(?) that are reabsorbed get reused by the parent neuron the next time it gets fired, but what happens to the rest?
    What happens to the ones that were used to activate other neurons? Do they attach to the dendrites? Then what? I’m betting they don’t just stick to the dendrites clogging them up so that ultimately they can’t be used anymore. Do they get re-uptaken through the dendrites so that the newly activated neuron can use them? Do they drift off and either get reabsorbed by the parent axon or join the pool of the “lost” molecules?
    And what happens to the “lost” neurotransmitter molecules? Do they dissolve somehow or get broken down some other way? Are they picked up by some vehicle that carries them to somewhere they can be recycled or disposed of in some bodily fluid? Do they drift through the space between neurons until they get picked up by a dendrite or an an axon, no matter how long that takes??

    Part 2:
    Neurotransmitter tests claim to be able to tell if you have a deficiency in any number of transmitters, hormones and a whole host of other things. What do they actually test for and where (in what part of the body)? It’s not a brain biopsy; they’re testing humours of the body, not drilling a hole in your skull to take a sample. But, for example, couldn’t you have too much serotonin in your gut, but not enough in your head? Is that even possible? Would such test be able to account for that?
    Any information I can find on this is mostly just trying to sell me a home testing kit, or trying to convince the reader that they need meds. Mostly I’m wondering what level of scamminess this is.

    Part 3:
    The general claim about SSRIs is that they increase serotonin levels in the brain, which (sometimes) helps to relieve depression, anxiety, etc. Do they actually increase serotonin levels? And Where/how? Everything I can find basically says you can’t increase serotonin levels directly. You might be able to take something containing one or more of its precursors, but that doesn’t seem to be what SSRIs are.
    Or do SSRIs do what’s implied in the name, inhibiting the reuptake mechanism of axons?

    Part 4 (aka, the actual point):
    I’m going to assume that “lost” neurotransmitter molecules get dumped into the body’s disposal system and come out in our urine, because that seems simplest and most logical to me. I’m also going to assume that neurotransmitter tests are a very basic urine test, because that’s pretty much what they say they are.
    Then if we assume that SSRIs do what it says on the tin and inhibit re-uptaking, there will be more “lost” serotonin molecules floating around our brain. Those molecules get dumped into the disposal system and come out in our urine, which increases the level of serotonin in our urine. BUT those molecules are ones that would have otherwise been reuptaken and retained in our neurological system. If the neurotransmitter test is a basic urine test, it will indeed look like we’ve increased our serotonin levels, but actually we’re just dumping them faster, leaving us with a serotonin deficiency in our brain.
    Does this make any sense? Could SSRIs actually cause a deficiency that looks like an increase???

    I would LOVE to have an expert answer, or some research papers on this, or even just someone who actually considers my questions and gives me their non-expert opinion. I’m frustrated by doctors looking at me like I’m an idiot who would never understand the answers that I’m looking for and is wasting their time, telling me “don’t worry about that” and then suggesting I should increase my meds, not taper off of them.

    So any thoughts you (or anyone) has would be appreciated. Or any pointers on where/who I should ask these questions.


    Your questions are so far beyond my comprehension level?, but I just want to say that I think it is great that you are so informed and asking questions!!!!


    I’m not Kati, and I’ve only done intro Biopsychology, but I’ll try to answer what I can.

    Part 1:
    The neurotransmitters that aren’t taken back into the axon are taken apart by astrocytes (which are a glia cell, which is another part of the matter in your brain). Astrocytes are basically the recycling machines of your brain. The bits and pieces then (to my best guess, although this is surprisingly not elaborated on in my text book) sent back into neuron to be used for further creation of neurotransmitters. Further to that, just because a neurotransmitter has re-entered the axon doesn’t mean it’s going to be used again. There’s something called Mono-amine oxidase in the neuron that breaks down neurotransmitters into their smaller parts. That’s why some of the earlier antidepressants (Mono-amine oxidase inhibitors – MOAIs) worked – they increased the concentration of serotonin and catecholamines in the neuron, therefore meaning more end up getting transmitted when the neuron is told to release them.

    Part 2:
    Never heard of it, sorry! But maybe they test for the precursors to neurotransmitters that are sent through the blood brain barrier to neurons, like dopa (dopamine) and tryptophan (serotonin). If they’re based on concentration in the blood, that could be assumed to be uniform across your body and be a good indication of the levels in your brain?

    Part 3:
    SSRIs increase the CONCENTRATION of serotonin in your brain, by keeping them in the synapse rather than in the neuron, where they can bind to the dendrite again and again and do their job. So they don’t increase the amount of serotonin in the brain per se, just the amount being used at any particular time.

    Part 4:
    I think that links back to my answer to part 1, but to my knowledge it doesn’t end up in your urine, it just ends up going back to your brain. But like I said, that’s my uneducated guess since it wasn’t actually covered in my textbook.

    I can’t point you to any specific research papers, but any biological psychology textbook should give you a more indepth overview than most google searches. If you feel like wading through thousands of research papers, is google’s academic research resource, but A LOT of the stuff on there will only give you an abstract, and require payment for the full article (unless you go to uni and your uni is affiliated with the site, which should allow you to access it for free… should.)

    I hope I haven’t gotten anything tooooo wrong… my final exam is on Friday, so I’d love if someone corrected me before then haha!



    OMG, Thank You. I might (will probably) have more questions once I’ve worked/thought through the new information in your answer, but I definitely had some mistaken assumptions.
    Thank you SOOOO much.


    No worries! Glad I could help 🙂

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