Understanding the Clinical Relevance and Non-Validity of Neurotransmitter Testing

Datis Kharrazian, DC, DHSc, MNeuroSci, MS, FAACP, DACBN, DABCN, DIBAK, CNS

Assistant Professor of Clinical Neuroscience for the Carrick Institute

Methods of Neurotransmitter Testing and Applications

Neurotransmitters are important cell signaling messengers that have profound impacts on systemic physiology and are not just limited to brain function. Neurotransmitters such as serotonin, dopamine, epinephrine, acetylcholine are also produced in the peripheral system such as the gastrointesitinal tract, kidneys, T-cells, smooth muscle end organs, and autonomic tissues.[i] [ii] [iii] [iv] The functions of neurotransmitters in the peripheral nervous system are completely independent of their functions in the central nervous system. Therefore, the influence of neurotransmitters in the peripheral nervous system cannot be correlated with influences on the central nervous system

In recent years, the testing of neurotransmitters by urinary testing has become popular in alternative medicine strategies to assess central nervous system imbalances, but the inferences from urinary testing to central nervous system imbalances are incorrect. The logic for testing urinary peripheral neurotransmitters to identify imbalances in central nervous system would be comparable to measuring hormones in the cerebrospinal fluid (CSF) for a menopausal patient. Hormones in the CSF are specific to hormones that influence the central nervous system and not the peripheral system. However, serum (not CSF) testing of hormones would be appropriate to assess the influence of hormones on peripheral tissues such as bones, arteries, organs, etc. The same logic applies to neurotransmitters, you cannot measure peripheral neurotransmitters in the urine to assess the function of central neurotransmitters

Laboratory analysis of neurotransmitters can be assessed either in the urine, serum, platelets or CSF. Each method of analysis has different inferences and very little correlation with each other.[v] CSF assessment appears to be the only appropriate method for testing levels of neurotransmitters that are produced and utilized in the central nervous system. Serum measurements of neurotransmitters are too minute to be analyzed functional and only serve roles in identifying catacholamine and serotonin generating tumors.[vi] Platelet measurements are limited to certain neurotransmitter and its associations with CSF have not been clearly substantiated. It appears that urinary neurotransmitter reflect measurements of neurotransmitters in the periphery, not in the brain.

A urinary serotonin test is more likely a measurement of the neurotransmitter produced in the peripheral gastrointestinal enteric nervous system than serotonin produced in the central mesencephalic raphe nuclei. Urinary epinephrine and norepinephrine measurements are most likely peripheral adrenal medulla output rather than central pontine locus ceruleus production. Urinary dopamine output is more likely peripheral adrenal medulla, renal and T-cell output rather than central mesencephalic substania nigra production. Urinary acetylcholine output is most likely peripheral nervous system byproduct than acetylcholine produced in the central basal nucleus of Meynert in the basal forebrain. In summary, urinary neurotransmitters may be used to assess output in the periphery, but it cannot be used to clinically evaluate neurotransmitter deficiencies in the brain.

The central nervous system is efficiently organized to produce its own neurotransmitters and does not depend upon neurotransmitters from the peripheral systems. For example, dopamine made in the substania nigra in the ventral tegmentum of the mesencephalon is delivered to areas in the basal ganglia that are anatomically organized and known as nigrostriatal projections. All central nervous system neurotransmitter producing nuclei have similar anatomical projections to areas of the brain that utilize the cellular messenger.[vii] Additionally, peripheral neurotransmitters such as dopamine cannot cross the blood-brain-barrier. In summary, the central nervous system produces its own neurotransmitters and does not depend upon peripheral production for function.[viii] Additionally, the only true reflection of central nervous system neurotransmitter output and availability is CSF. Urinary neurotransmitter levels cannot be used to assess brain neurotransmitter levels.

A Critical Look at Quantitative Neurotransmitter Assessment

Even if routine CSF neurotransmitter studies were easy to perform, or if we disregard the previous points made about urine, platelet, and serum testing inaccuracies to brain function, laboratory measurements of neurotransmitters would still be of very limited use clinically when evaluated in isolation. Neuronal signaling from post-synaptic neuronal clefts involves complex orchestration of many variables that must be assessed beyond an isolated assay of a neurotransmitter quantity. An isolated measurement does not take into account clinical variables such as uptake mechanisms, receptor site sensitivity, carrier protein ratios, the type of receptor sites (ex D1 or D2 for dopamine), degradation rates, and agonist and antagonistic influences from other messengers. The influences of all these variables are independent of an isolated quantitative neurotransmitter assay but what dictate the neuronal proteomic response.[ix]

Although neurotransmitters produced in the central nervous system are specific to certain nuclei, in a normal nervous system there is no correlation between quantitative testing of neurotransmitters to certain tracts and regions of the central nervous system. For example, the amount of serotonin found in the descending raphe-spinal pathways for pain modulation, and the amount of serotonin found in the frontal eye fields for eye movements, the amount of serotonin found in the pontine-genicualate-occiptal pathways for vision may all be completely different. Additionally, correlations between neuronal tissue levels of a neurotransmitter and frequency of firing rates have yet to be established clearly. This is especially true for functional imbalances that neurotransmitter testing is promoted to identify.

Non-Valid Applications of Neurotransmitter Testing and Clinical Practice

Many medications and natural supplements used in healthcare to modulate neurotransmitter responses impact physiology by modulating receptor site sensitivity, synaptic cleft degradation and reuptake mechanisms. Therefore, these compounds can have profound impact on neuronal responses related to neurotransmitters, but never change quantitative laboratory measurements. Medications used to impact brain neurotransmitter activity include mechanisms that modulate receptor site channel potentials, modulate receptor site binding sites, modulate degradation enzymes in the synaptic cleft, modulate transporter proteins, and modulate uptake mechanisms in the synaptic cleft. It is important to note that these changes are specific to chemical responses at the receptor site and synaptic cleft. These chemical changes do not influence the quantity of neurotransmitter levels, and therefore quantitative neurotransmitter testing is clinically invalidated with use of central modulating medications.

Many natural supplements also impact brain chemistry at the receptor site or synaptic cleft level that would invalidate quantitative testing of neurotransmitters clinically. Valerian root extract is a botanical used to impact GABA activity in the brian.[x] The mechanism of action appears to be on the GABA neurotransmitter receptor system and not on the increased synthesis of GABA. Valerian Extracts appear to have some affinity and expression of the GABA receptor site.[xi] [xii] [xiii] [xiv] [xv] [xvi] [xvii] The Valerenic acid compound of valarian has been shown to have an inverse agonist effect at adenosine A1 receptor sites, which also produces inhibitory central nervous system effects.[xviii] Valerian root extract influences receptor site activity and therefore quantitative GABA measurements while taking this compound would be invalid.

Galantamine is an unaltered extract from the caucasian snowdrop plant and has been used for the treatment of the central nervous system effectively for decades in Eastern Europe.[xix] [xx] The plant compound has the ability to inhibit the production of acethylcholineesterase and increase the sensitivity of acetylcholine receptor sites. [xxi] [xxii] [xxiii] [xxiv] Galantamine has powerfull acetylcholinergic impacts on the nervous system, but it does not appear to raise acetylcholine levels past the synaptic cleft and therefore the use of acetylcholine quantitative measurements are not valid to assess the impact of this compound.

Lithium orotate supplementation has the ability to increase acetylcholine synpatic cleft turnover, inhibits choline transport, and increases GABA receptor site activity.[xxv] [xxvi] The neurochemical influences of lithium in the brain are not related to quantitative changes of neurotransmitters. Therefore, although lithium orotate has profound impacts on central nervous system chemistry, its influences cannot be determined by neurotransmitter quantitative measurements.

L-Huperzine A is a potent alkaloid that is derived from club moss (Huperzia serreta). It is a very potent and specific acetylcholine esterase inhibitor resulting in decreased breakdown of acetylcholine and in increased levels of the neurotransmitter in the synaptic cleft regions of the brain. [xxvii] [xxviii] [xxix] [xxx] These changes will not reflect in changes of quantitative neurotransmitter testing.

Passionflower extract has historically been used for anxiety insomnia, seizures, and hysteria associated with GABA deficiency. Its mechanism of action is on modulating the sensitivity of the GABA receptor system. [xxxi] [xxxii] [xxxiii] [xxxiv] [xxxv] [xxxvi] [xxxvii] The botanicals influence is at the receptor site and therefore the use of the botanical will not demonstrate changes with quantitative neurotransmitter testing.

St. John’s wart is also known as Hypericum perforatum and the active constituents include hyperforin, hypericin and tannins. The botanical compounds have shown to increase serotoninergic activity by acting as a selective serotonin reuptake inhibitor.[xxxviii] [xxxix] [xl] [xli] [xlii] [xliii] [xliv] [xlv] [xlvi] The neurochemical changes produced by reuptake mechanisms are specific to the synaptic cleft and not clinically measurable with quantitative serotonin measurements.

Many natural supplements that effectively modulate brain neurochemistry do so by their influences at receptor sites and synaptic cleft transmission and not by increased production of the neurotransmitter substrate. When compounds such as these are used the quantity of the neurotransmitter measured becomes clinically irrelevant. The use of these compounds may increase synaptogenic activity of the brain, but demonstrate absolutely limited changes with assay.

On the other hand, there are numerous amino acid based supplements that actually change neurotransmitter quantitative levels in the periphery and in the central nervous system. It is important to understand that only precursors that can cross the blood-brain-barrier have potentials to change levels in the central nervous system. Additionally, precursor enzymes to convert amino acids into neurotransmitters are found in both the central and peripheral nervous system. The type of neurotransmitter testing will most likely reflect in which system changes took place. CSF neurotransmitter measurements reflect central nervous system influences and urinary neurotransmitter measurements reflect peripheral nervous system changes. The influence of neurotransmitters in the peripheral nervous system cannot be correlated with influences on the central nervous system accurately.

5-Hyrdoxytryptophan (5-HTP) is an amino acid precursor to serotonin. Supplementation with 5-HTP has been shown to increase serotonin levels in both the central and peripheral nervous system. .[xlvii] [xlviii] [xlix] [l] [li] [lii] [liii] [liv] [lv] Oral supplementation with 5-HTP will impact brain neurotransmitter levels but a large portion of conversion is in the gastrointestinal tract enteric nervous system. The amounts of serotonin produced in the gastrointestinal tract are used for local responses and do not reflect changes in the brain.[lvi] [lvii] [lviii] Urinary serotonin testing after the administration of 5-HTP most likely reflects peripheral conversion into serotonin, not brain.

Alpha-GPC (L-alpha-glycerlphosphorylcholine) is a phospholipid metabolite that is isolated from lecithin. It is very well absorbed by the gastrointestinal tract and crosses the blood brain barrier where it is used for the synthesis of acetylcholine. Oral intake of Alpha GPC has been shown to increase acethylcholine levels in the brain as determined by tissue analysis.[lix] [lx] It is unlikely that oral intake of Alpha-GPC levels that change brain acetylcholine levels would be reflected accurately with urine assay.

It is important to note that using amino acid precursors such as Alpha-GPC, tyrosine, 5-HTP, and tyrosine are likely to promote increased synthesis of neurotransmitters, but these changes take place both peripherally and centrally. It is not valid to conclude that a urinary neurotransmitter testing demonstrates the quantitative measurements that are taking place in the brain. For example, oral tyrosine intake may increase urinary catacholamine levels, that does not mean that the changes found in the urine are comparable to CSF and brain. Oral tyrosine intake most likely is being converted to catacholamines by the adrenal medulla and renal systems. These changes do not reflect brain specifically. To summarize, although precursor amino acids can increase neurotransmitter levels both peripherally and centrally, urinary testing most likely reflects peripheral changes.

Summary and Conclusion

The model of conducting urinary neurotransmitters to measure brain neurochemistry is completely unsubstantiated. The levels of neurotransmitters found in the urine most likely reflect neurotransmitter levels in the peripheral system and not brain. Although precursor amino acids are effective in raising levels of neurotransmitters the levels measured by urinary testing are a reflection of peripheral conversion and cannot effectively correlate with brain. Additionally, many botanical compounds improve neurotransmitter synaptic activity by enhancing neurotransmitter receptor site sensitivities, synaptic cleft uptake, and degradation processes. These influences will change brain synaptic expression, but not change quantitative levels of neurotransmitters.