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Brain Scans Reveal Dopamine Neuron Damage in Long COVID
Confirmed
In Short: Brain scans like these measure a protein found on dopamine nerve endings rather than measuring neuron density directly.
Scientists have discovered a distinct change in the brains of people with long COVID that might explain some of the illness's most debilitating symptoms, according to a preliminary study in Canada.
The study, published in eBioMedicine, involved 24 people with long COVID and compared their brain scans to those of healthy participants.
Compared to healthy controls, the brains of long COVID patients showed a reduction in the density of dopamine nerve endings within several regions of the striatum.
Roughly 25 percent of the variance in symptoms among patients with long COVID was associated with a loss of dopaminergic neurons.
Dopamine is a crucial chemical messenger in the brain, closely tied to the brain's reward system and involved in motivation, movement, and thinking.
The worse the symptoms of memory decline, slow physical movements, and a lack of motivation, the greater the differences measured in dopamine nerve endings.
"Our findings provide compelling evidence that long COVID involves the loss of dopamine-releasing neurons," says psychiatrist Jeffrey Meyer from the Brain Health Imaging Center in Canada.
"These results indicate that long COVID is, at least in part, a disorder of the brain's dopamine system," argues Meyer.
For many people with long COVID, the infection ends but the exhaustion, slowed thinking, memory problems, and loss of motivation do not.
"This kind of injury is well known to produce symptoms like lack of motivation and motor slowing, and may contribute to memory difficulties in other neurological conditions," says Meyer.
"For five years I have been seeking answers on what happened to me after I contracted COVID in 2021," says Deuville.
It was a crushing loss of the life I had and the person I was before. The research of Dr Meyer brings hope. It also validates what long COVID sufferers have always known – long COVID is real, and the effects are devastating.
Background
Scientists found distinct changes in brain regions of people with long COVID, suggesting injury to dopamine neurons.
What's confirmed
- "This kind of injury is well known to produce symptoms like lack of motivation and motor slowing, and may contribute to memory difficulties in other neurological conditions. Our results suggest a similar process is occurring in long COVID."
- "For five years I have been seeking answers on what happened to me after I contracted COVID in 2021," says Deuville.
- The findings, published in eBioMedicine, provide the strongest evidence to date linking long COVID with injury to neurons that release dopamine, a chemical messenger involved in motivation, movement, and thinking.
- Previous work by Dr. Meyer and his colleagues found increased inflammation in the brains of people with long COVID, especially in regions containing large numbers of dopamine-releasing neurons.
- The latest scans found reduced dopamine neuron markers in those regions, and the extent of the reductions was associated with patients’ symptoms.
- New PET imaging findings suggest that some of long COVID’s most disabling symptoms may stem from disruption of the brain’s dopamine system.
- For many people with long COVID, the infection ends but the exhaustion, slowed thinking, memory problems, and loss of motivation do not.
- Researchers have struggled to explain why these symptoms persist because the underlying changes inside the brain have remained unclear.
- Brain scans from the Centre for Addiction and Mental Health (CAMH) now point to a possible part of the answer.
- Long COVID is estimated to affect five percent of the global population, including two million people in Canada.
- It includes symptoms such as fatigue, brain fog, memory difficulties, and low mood that continue for at least three months after the initial COVID-19 infection.
- Despite the scale of the problem, no evidence-based treatments are currently available, in part because researchers still do not fully understand the brain changes involved.
What's still developing
- One small autopsy study found fewer dopamine neurons in people who died with severe COVID-19, but most were elderly, and some had signs of early dementia, including one person with Parkinson's, which confounds the results.
- This new investigation is only preliminary, but it suggests that perhaps long COVID impacts dopamine-releasing neurons in broadly similar ways to Parkinson's.
- Dopamine is famously known as the 'feel-good' hormone.
- But there are reasons to suspect that dopamine circuits may be vulnerable to injury during long COVID.
- Individuals with long COVID show elevated markers for some brain cells that prune back synapses.
- It's also possible that SARS-CoV-2 can directly infect dopamine-releasing neurons, injuring them from within.
- These brain cells tend to have a high density of receptors that SARS-CoV-2 could theoretically connect to.
- "This is a notable shift from present therapeutic development, given that no current trials focus on augmenting functions of dopamine-releasing neurons."
- For the first time, brain-imaging researchers have identified specific neuron damage — specific cells, specific brain locations, specific symptoms — in patients who have been told for years there was nothing measurable to find.
- The study design required patients with confirmed long COVID to undergo PET scanning and complete detailed symptom questionnaires.
- It will test whether dopamine-targeted treatment measurably improves the three symptom clusters this study identified.
- The sample size was not reported in published detail, which limits the ability to estimate statistical power or determine whether results hold across the full range of long COVID severity and time since infection.