Long COVID, or post COVID-19 syndrome, is a condition that affects a small percentage of individuals who have recovered from a SARS-CoV-2 infection. A recent study from the University of Pennsylvania has shed light on the mechanisms underlying this condition, particularly the neurocognitive symptoms experienced by long COVID patients. The researchers found that long COVID patients have lower levels of serotonin, a neurotransmitter involved in mood regulation and other bodily functions. The decrease in serotonin levels is driven by an inflammation pathway mediated by SARS-CoV-2 viral RNA that persists in the gut. The study also revealed that there is a correlation between the number of long COVID symptoms experienced by individuals and lower serotonin levels months later. The findings suggest that low serotonin levels could serve as a biomarker for long COVID and that interventions targeting serotonin signaling, such as selective serotonin reuptake inhibitors (SSRIs), should be explored in clinical studies.
The study also found that a subset of long COVID patients still had traces of the virus in their stool samples, indicating that it had persisted in the gut. This persistence of the virus in the gut leads to an immune reaction and inflammation, which reduces serotonin storage and blocks the uptake of tryptophan, a precursor of serotonin. Interestingly, serotonin levels in the brain were found to be normal in mice, but the signaling of nerves outside of the brain, including the vagus nerve, was reduced. This reduction in nerve signaling was associated with memory impairments in the mice. The researchers suggest that the findings of this study may have implications beyond long COVID and could potentially apply to other post-viral conditions.
The lack of understanding surrounding long COVID has made it challenging for researchers and doctors to provide effective treatments for patients. Therefore, the findings of this study provide valuable insights and potential avenues for diagnosis and treatment. The researchers believe that their findings support the exploration of SSRIs and other interventions targeting serotonin signaling in clinical trials to alleviate the neurocognitive symptoms associated with long COVID. Further research is needed to fully understand the mechanisms underlying long COVID and to determine if similar pathways are involved in other post-viral syndromes.