Scientists have found signs of inflammation and neurodegeneration in the brains of people who have died from Covid-19, similar to those found in people who die from diseases like Alzheimer’s and Parkinson’s.
The results from researchers at the Stanford School of Medicine, USA, and Saarland University in Germany could help explain why many Covid-19 patients report neurological problems.
These complaints increase with more severe cases of Covid-19 and may persist as an aspect of “Long Covid,” a long-lasting illness that sometimes occurs after being infected with SARS-CoV-2, the virus that causes Covid-19 .
About a third of people hospitalized for Covid-19 report symptoms of blurred thinking, forgetfulness, difficulty concentrating and depression, said Tony Wyss-Coray, a professor at Stanford.
The researchers couldn’t find any signs of SARS-CoV-2 in the brain tissue they received from eight people who died from the disease. Brain samples from 14 people who died of other causes were used as controls for the study.
“The brains of patients who died from severe Covid-19 showed profound molecular markers of inflammation, although no clinical signs of neurological impairment were reported in these patients,” said Wyss-Coray.
The blood-brain barrier consists partly of blood vessel cells that are tightly sewn together, and blob-like abutments that are created when the protrusions of the brain cells are pressed together against the vessels.
Until recently, it was thought to be extremely selective in accessing cells and molecules produced outside the brain.
However, previous work by Wyss-Coray’s group and others has shown that blood borne factors outside the brain can signal through the blood-brain barrier to ignite inflammatory responses in the brain.
The latest study, published in the journal Nature, found that activation levels of hundreds of genes in all major cell types in the brain in the brains of Covid-19 patients differed from those of the control group.
Many of these genes have been linked to inflammatory processes, the researchers said.
There were also signs of stress in neurons in the cerebral cortex, the region of the brain that plays a key role in decision making, memory, and mathematical reasoning.
These neurons, which are mainly of two types – excitatory and inhibitory, form complex logic circuits that carry out these higher brain functions.
The outermost layers of the cerebral cortex of patients who died of Covid-19 showed molecular changes that indicate suppressed signaling from excitatory neurons, along with increased signaling from inhibitory neurons, which act like brakes on excitatory neurons.
This type of signal imbalance has been linked to cognitive deficits and neurodegenerative diseases such as Alzheimer’s and Parkinson’s, the researchers said.
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