# are neurotransmitters present in circulating blood? **URL:** \ **Category:** Factual Questions\ **Created:** [May 7, 2019, 7:41pm UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631 "2019-05-07T19:41:37Z")\ **Posts on this page:** 17\ **Page:** 1
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [May 7, 2019, 7:41pm UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/1 "2019-05-07T19:41:37Z")
When there are surges and deficits of various neurotransmitters in a person’s body (brain), is there any signal in the circulating blood that those levels have changed? Or, related, how do we know that a person has a surfeit or a deficit of serotonin or dopamine, for instance? I’m wondering if there are relatively simple ways of finding signs of anxiety or depression or contentment in a person’s blood - presumably indicators of higher or lower levels of neurotransmitters that would reveal emotional state. ---
**Author:** ![KarlGauss](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/karlgauss/32/3713_2.png) [@KarlGauss](https://boards.straightdope.com/u/KarlGauss)\ **Post date:** [May 7, 2019, 9:28pm UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/2 "2019-05-07T21:28:13Z")
I am not even close to an expert in the area but am pretty much confident that no such substances/correlations have been detected. One thing to keep in mind is that the brain get a lot of signals from substances floating around _within_ it, in the cerebrospinal fluid (CSF). I mean deep inside the brain, at the very centre - located symmetrically about the centre of the brain are the ventricles which are full of CSF, and similarly full of lots of transmitters, hormones, etc., many of which have not been characterized. Given the short half lives of some of the neurotransmitters found in CSF, it would be extremely hard to correlate them with blood levels of the classical hormones and transmitters (with catecholamines, for example, functioning both as hormones and as neurotransmitters). The _fundamental_ location of these CSF-containing ventricles is nicely shown in the GIF in [this wikipedia link](https://en.wikipedia.org/wiki/Ventricular_system). If the brain is built to have the CSF located in the most intimate proximity to the most fundamental and ‘vegetative’ centres in the deepest part of the brain (e.g. hypothalamus), you can be confident that the substances in the CSF are of major importance to things like emotions. ETA: Raging emotions can be induced in lab animals by lesioning their hypothalami. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [May 7, 2019, 9:50pm UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/3 "2019-05-07T21:50:20Z")
There are blood [tests](https://www.mayocliniclabs.com/test-catalog/Clinical+and+Interpretive/84373) for serotonin levels, for example. A person starting on a drug to increase serotonin levels might have such a test done a couple of times. But people are so highly variable it is probably not diagnostic of whether a particular person has a given mood disturbance. What a good level is for one person might be bad for another. (The way neural connections respond to different levels of transmitters is wide ranging.) If there is something really out of whack, serotonin syndrome from suspected drug use, a tumor, etc., then such a test can be helpful. ---
**Author:** ![thelurkinghorror](https://avatars.discourse-cdn.com/v4/letter/t/7c8e57/32.png) [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)\ **Post date:** [May 7, 2019, 11:56pm UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/4 "2019-05-07T23:56:17Z")
As the link above, many tests done measure metabolites like 5-HIAA of serotonin etc., not the NT itself. NTs are generally resident in the synapse, not the bloodstream. Chemicals that signal in the circulatory system are called hormones. The exact mechanisms may differ, but the distinction is generally where the activity takes place and how far they travel. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [May 8, 2019, 2:46am UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/5 "2019-05-08T02:46:20Z")
I thought that cortisol, for instance, could be detected in the blood. I guess that’s not a neurotransmitter but it is a chemical indicator of emotional state, i.e. stress. From \*\*Dr. Gauss’s \*\*remarks, I gather that many of the psychopharmacological drugs e.g. antidepressants, antianxiolytics, that are prescribed for various emotional disturbances or conditions are based on guesswork and symptoms, as opposed to actual chemical signs in the blood. ---
**Author:** ![pool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pool/32/4152_2.png) [@pool](https://boards.straightdope.com/u/pool)\ **Post date:** [May 8, 2019, 3:02am UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/6 "2019-05-08T03:02:35Z")
I believe a lot of neurotransmitters like serotonin cannot be observed directly it is in fact neurotransmitter transporters that can, I went to school for radiation therapy, but some of the nuclear medicine technologist majors that we took physics with, talked about this in their oral presentations. ---
**Author:** ![jackdavinci](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackdavinci/32/3259_2.png) [@jackdavinci](https://boards.straightdope.com/u/jackdavinci)\ **Post date:** [May 8, 2019, 4:41am UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/7 "2019-05-08T04:41:27Z")
This kind of brings up an implied issue - it seems like there is some disconnect or disparity between the amount of detail we seem to have about neurochemistry in the brain, and the relative poverty of related diagnostic tools. So then the question becomes, if it is so difficult to detect what is happening chemically in a patient brain, by what method did we determine what we know generally? Normally my instinct would be to imagine animals or dead humans. But in both cases the nature of the particular medium would seem to require a living subject and minimally intrusive or invasive procedures to get anything resembling good data. ---
**Author:** ![Anaglyph](https://avatars.discourse-cdn.com/v4/letter/a/ed8c4c/32.png) [@Anaglyph](https://boards.straightdope.com/u/Anaglyph)\ **Post date:** [May 8, 2019, 8:46am UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/8 "2019-05-08T08:46:10Z")
Many of these substances have several types of receptors, and their release into blood and into the synaptic cleft are differentially regulated. e.g. [The roles of peripheral serotonin in metabolic homeostasis - PubMed](https://www.ncbi.nlm.nih.gov/pubmed/26070423) “The roles of peripheral serotonin in metabolic homeostasis. Metabolic homeostasis in the organism is assured both by the nervous system and by hormones. Among a plethora of hormones regulating metabolism, serotonin presents a number of unique features. Unlike classical hormones serotonin is produced in different anatomical locations. In brain it acts as a neurotransmitter and in the periphery it can act as a hormone, auto- and/or paracrine factor, or intracellular signaling molecule. Serotonin does not cross the blood-brain barrier; therefore the two major pools of this bioamine remain separated. Although 95% of serotonin is produced in the periphery, its functions have been ignored until recently. Here we review the impact of the peripheral serotonin on the regulation of function of the organs involved in glucose and lipid homeostasis.” ---
**Author:** ![Ann\_Hedonia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ann_hedonia/32/319_2.png) [@Ann\_Hedonia](https://boards.straightdope.com/u/Ann_Hedonia)\ **Post date:** [May 8, 2019, 2:06pm UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/9 "2019-05-08T14:06:03Z")
> [@jackdavinci](#): > > This kind of brings up an implied issue - it seems like there is some disconnect or disparity between the amount of detail we seem to have about neurochemistry in the brain, and the relative poverty of related diagnostic tools. > > So then the question becomes, if it is so difficult to detect what is happening chemically in a patient brain, by what method did we determine what we know generally? > > Normally my instinct would be to imagine animals or dead humans. But in both cases the nature of the particular medium would seem to require a living subject and minimally intrusive or invasive procedures to get anything resembling good data. IIRC, the medical establishment has never found a linkage between neurotransmitter levels and mental illness. If anyone told you your anxiety and depression was the result of a chemical imbalance, they misunderstood or you misunderstood. [https://www.mentalhealthexcellence.org/nuances-narratives-chemical-imbalance-debate-psychiatry/](https://www.mentalhealthexcellence.org/nuances-narratives-chemical-imbalance-debate-psychiatry/) ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [May 8, 2019, 5:16pm UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/10 "2019-05-08T17:16:05Z")
> [@Ann\_Hedonia](#): > > IIRC, the medical establishment has never found a linkage between neurotransmitter levels and mental illness. If anyone told you your anxiety and depression was the result of a chemical imbalance, they misunderstood or you misunderstood. > > [https://www.mentalhealthexcellence.org/nuances-narratives-chemical-imbalance-debate-psychiatry/](https://www.mentalhealthexcellence.org/nuances-narratives-chemical-imbalance-debate-psychiatry/) This is completely against well established medical studies. That site sounds a lot like a Scientology front or some such. A _lot_ of people have been helped by things like, for example, [serotonin-reuptake inhibitors](https://www.mayoclinic.org/diseases-conditions/depression/in-depth/ssris/art-20044825) whose purpose is to increase or decrease the amount of certain neurotransmitters. Your link is appalling uninformed, unhelpful and dangerous to the mental health of people who can be helped by actual Science. ---
**Author:** ![Ann\_Hedonia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ann_hedonia/32/319_2.png) [@Ann\_Hedonia](https://boards.straightdope.com/u/Ann_Hedonia)\ **Post date:** [May 8, 2019, 10:15pm UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/11 "2019-05-08T22:15:56Z")
> [@ftg](#): > > This is completely against well established medical studies. That site sounds a lot like a Scientology front or some such. > > A _lot_ of people have been helped by things like, for example, [serotonin-reuptake inhibitors](https://www.mayoclinic.org/diseases-conditions/depression/in-depth/ssris/art-20044825) whose purpose is to increase or decrease the amount of certain neurotransmitters. > > Your link is appalling uninformed, unhelpful and dangerous to the mental health of people who can be helped by actual Science. Here’s a better link. Harvard is usually pretty straightforward. > **[What causes depression? - Harvard Health](https://www.health.harvard.edu/mind-and-mood/what-causes-depression)** > > Depression has many possible causes, including faulty mood regulation by the brain, genetic vulnerability, stressful life events, medications, and medical problems. It's believed that several of th... I am not saying that anti-depressants don’t help people. I’m saying that the causes of mental illness are complex and varied and not fully understood. As are the mechanisms by which anti-depressants work. Yes, SSRI’s help people. But they don’t help by curing a measurable serotonin deficiency. ---
**Author:** ![Ann\_Hedonia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ann_hedonia/32/319_2.png) [@Ann\_Hedonia](https://boards.straightdope.com/u/Ann_Hedonia)\ **Post date:** [May 8, 2019, 10:47pm UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/12 "2019-05-08T22:47:41Z")
Here’s an article from Scientific American with some interesting details on the many mechanisms of SSRI medication. > **[Unraveling the Mystery of How Antidepression Drugs Work](https://www.scientificamerican.com/article/unraveling-the-mystery-of-ssris-depression/)** > > New insights into how selective serotonin reuptake inhibitors work suggest they reverse inhibited nerve regeneration and connectivity that may underlie depression ---
**Author:** ![Surreal](https://avatars.discourse-cdn.com/v4/letter/s/eada6e/32.png) [@Surreal](https://boards.straightdope.com/u/Surreal)\ **Post date:** [May 8, 2019, 11:55pm UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/13 "2019-05-08T23:55:09Z")
> [@ftg](#): > > Your link is appalling uninformed, unhelpful and dangerous to the mental health of people who can be helped by actual Science. > **[When It Comes To Depression, Serotonin Isn't The Whole Story](https://www.npr.org/sections/health-shots/2012/01/23/145525853/when-it-comes-to-depression-serotonin-isnt-the-whole-story)** > > The antidepressant Prozac selectively targets the chemical serotonin. When the drug was introduced in the 1980s, it helped solidify the idea in many minds that depression was the result of a chemical imbalance. But the real story is far more... > [@](#): > > **“Chemical imbalance is sort of last-century thinking. It’s much more complicated than that,” says Dr. Joseph Coyle, a professor of neuroscience at Harvard Medical School. “It’s really an outmoded way of thinking.”** > > Coyle, who is also the editor of the journal Archives of General Psychiatry, says that though serotonin plays a role in depression, low serotonin is likely not the cause of depression. Scientific thinking has clearly shifted, he says. ---
**Author:** ![thelurkinghorror](https://avatars.discourse-cdn.com/v4/letter/t/7c8e57/32.png) [@thelurkinghorror](https://boards.straightdope.com/u/thelurkinghorror)\ **Post date:** [May 9, 2019, 5:14am UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/14 "2019-05-09T05:14:22Z")
> [@CC](#): > > I thought that cortisol, for instance, could be detected in the blood. I guess that’s not a neurotransmitter but it is a chemical indicator of emotional state, i.e. stress. From \*\*Dr. Gauss’s \*\*remarks, I gather that many of the psychopharmacological drugs e.g. antidepressants, antianxiolytics, that are prescribed for various emotional disturbances or conditions are based on guesswork and symptoms, as opposed to actual chemical signs in the blood. It is a hormone. Again, the distinction isn’t based on the chemical, e.g. norepinphrine can be a neurotransmitter, a hormone, or the third category: neuromodulator. > [@ftg](#): > > This is completely against well established medical studies. That site sounds a lot like a Scientology front or some such. I can’t find any links to Scientology but it does sound nutty. Some new age thing. The name of the group really makes me think of the First Annual Montgomery Burns Award for Outstanding Achievement in the Field of Excellence. > [@](#): > > A _lot_ of people have been helped by things like, for example, [serotonin-reuptake inhibitors](https://www.mayoclinic.org/diseases-conditions/depression/in-depth/ssris/art-20044825) whose purpose is to increase or decrease the amount of certain neurotransmitters. > > Your link is appalling uninformed, unhelpful and dangerous to the mental health of people who can be helped by actual Science. Some drugs increase or decrease NT levels directly, but SSRIs work by retarding reuptake (recycling) of serotonin and keeping it in the synapse longer, therefore increasing effect. ---
**Author:** ![Ann\_Hedonia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ann_hedonia/32/319_2.png) [@Ann\_Hedonia](https://boards.straightdope.com/u/Ann_Hedonia)\ **Post date:** [May 9, 2019, 12:02pm UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/15 "2019-05-09T12:02:26Z")
I’m going to apologize for posting that first link, but not for the content of the story. The same story was published in a few different places and I copied the wrong link out of my search engine. I meant to link to it here. [https://www.psychiatrictimes.com/couch-crisis/nuances-narratives-and-chemical-imbalance-debate](https://www.psychiatrictimes.com/couch-crisis/nuances-narratives-and-chemical-imbalance-debate) ---
**Author:** ![Anaglyph](https://avatars.discourse-cdn.com/v4/letter/a/ed8c4c/32.png) [@Anaglyph](https://boards.straightdope.com/u/Anaglyph)\ **Post date:** [May 9, 2019, 12:38pm UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/16 "2019-05-09T12:38:24Z")
In the case of depression, it seems to be the long-term adaptation of your brain to the increased concentrations of serotonin and dopamine neurotransmitters rather than the direct effect of increased neurotransmitter concentrations that alleviates the symptoms - while re-uptake inhibitors or monoamine oxidase inhibitors inhibiting their degradation increase the neurotransmitter concentrations very quickly, it takes several weeks to get the full effect of the treatment. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [May 9, 2019, 12:47pm UTC](https://boards.straightdope.com/t/are-neurotransmitters-present-in-circulating-blood/833631/17 "2019-05-09T12:47:15Z")
> [@thelurkinghorror](#): > > Some drugs increase or decrease NT levels directly, but SSRIs work by retarding reuptake (recycling) of serotonin and keeping it in the synapse longer, therefore increasing effect. And therefore the level at the synapse is higher.