In this study, researchers found that the genetic material from the virus and possibly other parts activate TLR3 receptors. These in turn cause the cells to release IFN1. IFN1 works on the intestinal cells via STAT1 pathway to down-regulate ACE2 receptors and B0AT1 channels. The result is reduced absorption of tryptophan leading to reduced serotonin production in the body. They also found that IFN1 activates platelets leading to micro thrombi and further reduction of serotonin as platelets are a huge reservoir of serotonin. Researchers also found that MAO activity was increased. Vagal activity was reduced leading to the hippocampal reduction in function as well. The researchers suggest using tryptophan precursor supplement (5HTP - 5 hydroxytryptophan) and SSRI medications to rescue serotonin levels in long COVID patients.

DrBeen: Medical Education Online
https://www.drbeen.com/

FLCCC | Front Line COVID-19 Critical Care Alliance
https://covid19criticalcare.com/

URL List (Nov. 24 2023)

Serotonin reduction in post-acute sequelae of viral infection: Cell
https://www.cell.com/cell/fulltext/S0092-8674(23)01034-6#gr2

Serotonin in Platelets - ScienceDirect
https://www.sciencedirect.com/science/article/abs/pii/B978012800050200005X

IJMS | Free Full-Text | The Mechanism of Secretion and Metabolism of Gut-Derived 5-Hydroxytryptamine
https://www.mdpi.com/1422-0067/22/15/7931

ijms-22-07931-g001.png (3550×2309)
https://www.mdpi.com/ijms/ijms-22-07931/article_deploy/html/images/ijms-22-07931-g001.png

Uptake and release of serotonin by blood platelets. Serotonin is taken... | Download Scientific Diagram
https://www.researchgate.net/figure/Uptake-and-release-of-serotonin-by-blood-platelets-Serotonin-is-taken-up-from-the_fig2_367097021

Indoleamine 2,3-dioxygenase - Wikipedia
https://en.wikipedia.org/wiki/Indoleamine_2,3-dioxygenase#:~:text=Indoleamine%2Dpyrrole%202%2C3%2D,female%20genital%20tract%20or%20placenta.

Frontiers | Kynurenine Pathway Metabolites as Biomarkers for Amyotrophic Lateral Sclerosis
https://www.frontiersin.org/articles/10.3389/fnins.2019.01013/full

Toll-like receptor 3 (TLR3) regulation mechanisms and roles in antiviral innate immune responses - PMC
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8377577/#:~:text=Toll%2Dlike%20receptor%203%20(TLR3)%20is%20a%20member%20of,establishing%20an%20antiviral%20host%20response.

Mechanisms of type-I- and type-II-interferon-mediated signalling | Nature Reviews Immunology
https://www.nature.com/articles/nri1604

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