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.