Long Covid is a chronic condition that occurs after SARS-CoV-2 infection. Between 10 and 35% of COVID-19 patients develop the condition, with neuropsychiatric and neurological symptoms such as anxiety, cognitive deficits, and fatigue being common. Previous studies have found that SARS-CoV-2 antigens linger in the bloodstream of patients with Long COVID.
In the current study, researchers investigated how SARS-CoV-2 antigens affect the brain and nervous system. To do so, they injected an antigen called S1- a subunit of the ‘spike’ protein- into the spinal fluid of rats. They then compared infected rats with an unaffected control group.
After 7 days, levels of cortisol-like hormone corticosterone fell by 31% in the hippocampus of rats exposed to S1. This drop increased to 37% at 9 days. Cortisol has anti-inflammatory effects and helps regulate the immune response. Research suggests that people with long COVID tend to have low cortisol levels.
In another experiment, the researchers exposed rats to an immune stressor and observed various measures, including immune cell activity in the brain, heart rate, and behavior. Rats previously exposed to S1 had a stronger response to the stressor, exemplified by more neuroinflammation, stronger activation of glial cells and changes, and changes in eating, drinking, core body temperature, heart rate, and behavior.
Further research is needed to understand whether these findings apply beyond mice to humans. In a press release, lead study author Matthew Frank, PhD, a senior research associate with the Department of Psychology and Neuroscience at the University of Colorado Boulder said that he doubts cortisol treatments could treat Long COVID alone, but that the findings suggest identifying and minimizing stressors may help manage symptoms.
“We show for the first time that exposure to antigens left behind by this virus can actually change the immune response in the brain so that it overreacts to subsequent stressors or infection. There are many individuals out there suffering from this debilitating syndrome. This research gets us closer to understanding what, neurobiologically, is going on and how cortisol may be playing a role," said Frank.
Sources: Science Daily, Brain, Behavior, and Immunity