Conversely, neurones that that communicate less, or not at all, have fewer synapses because they are removed, or pruned, by immune cells called microglia. The junctions between neurones that talk to each other frequently have more knob-shaped ends that produce neurotransmitters-chemicals that transmit signals to other neurones-which then travel across gaps between neurones known as a synaptic cleft. Synapses are responsible for all the functions of the brain, from memory to controlling movement to feeling emotions-and they are constantly remodelled. “Synapses are essentially how cells talk to each other and how information is passed from one part of the brain to another,” Lancaster says. The brain is made of a dense and dynamic network of nerve cells that communicate through synapses that change as humans learn. Pruning connections between neurones is essential for learning When this barrier is breached, pathogens, aberrant immune cells, and inflammatory compounds, can enter the cerebrospinal fluid and the brain. Using brain organoids, Lancaster’s research has revealed that SARS-CoV-2 damages the protective barrier of the brain. “This study fits in nicely with ours and several others,” says Madeline Lancaster, a neurobiologist at the U.K.'s MRC Laboratory of Molecular Biology in Cambridge. “This could be one of the many reasons-probably-why we are observing a range of neurological symptoms, even after the infection is long gone,” says Samudyata, a postdoctoral researcher at Karolinska Institute who led the study and goes by one name.Īna Osório Oliveira, a co-author and neuroscientist in Sellgren’s lab, says, “It was quite striking that very small amounts of the virus could quite rapidly spread in the organoids and eliminate an excessive number of synapses.” The research was published in the journal Molecular Psychiatry. Their research has led them to conclude that destroying too many connections between neurones, or over-pruning, may be causing brain fog in long COVID patients. One such condition, known as brain fog, causes disorientation, memory loss, chronic headache, and numbness, and it affects nearly 40 percent of long COVID patients.Ĭarl Sellgren, a psychiatrist and cellular biologist, and his team at the Karolinska Institute decided to use the organoids to try to learn what SARS-CoV-2 does to brain and whether it might help explain the neurological symptoms. In the last two years, scientists have documented long-lasting neural and behavioural problems in COVID-19 patients.
The discovery adds to the growing understanding of how SARS-CoV-2 enters the central nervous system and causes disease. When scientists at the Karolinska Institute in Sweden infected brain organoids-pinhead-size bits of brain tissue grown in the lab-with the virus that causes COVID, they found that it accelerated the destruction of connections between neurones called synapses.
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