New research suggests serotonin loss may be a key player in cognitive decline, rather than a side-effect of Alzheimer’s disease.
In a study examining the brain scans of people with mild loss of thought and memory ability, researchers report evidence of lower levels of the serotonin transporter — a natural brain chemical that regulates mood, sleep and appetite. Previous studies have shown that people with Alzheimer’s disease and severe cognitive decline also have severe loss of serotonin neurons, but the studies did not show whether those reductions were a cause or effect of the disease. Results of the new study of people with very early signs of memory decline, the researchers say, suggest that lower serotonin transporters may be drivers of the disease rather than a byproduct.
A report on the study, published in Neurobiology of Disease, also suggest that finding ways to prevent the loss of serotonin or introducing a substitute neurotransmitter could slow or stop the progression of Alzheimer’s disease and perhaps other dementias.
To further study serotonin’s role in cognition and neurodegenerative disease, the research team used brain positron emission tomography (PET) scans to look at levels of serotonin in the brains of people with mild cognitive problems, which may be a precursor of Alzheimer’s disease or other dementias.
The study paired 28 participants with mild cognitive impairment with 28 healthy matched controls. Participants were an average age of 66 and about 45 percent were women. Each participant underwent an MRI and PET scan to measure brain structures and levels of the serotonin transporter SERT. The researchers found that people with mild cognitive impairment had up to 38 percent less SERT detected in their brains compared to each of their age-matched healthy controls. And not a single person with mild cognitive impairment had higher levels of SERT compared to their healthy control.
Each participant also underwent learning and memory tests. On a scale of 0 to 80, with 80 reflecting the best memory, the healthy participants had an average score of 55.8, whereas those with mild cognitive impairment scored an average of 40.5.
With the Brief Visuospatial Memory Test, participants were shown a series of shapes to remember and draw later. From a scale of 0 to 36, with 36 being the top score, healthy people scored an average of 20.0 and those with mild cognitive problems scored an average of 12.6.
The researchers then compared the results from the brain imaging tests for the serotonin transporter to those two memory tests, and found that the lower serotonin transporters correlated with lower scores. For example, those people with mild cognitive impairment had 37 percent lower verbal memory scores and 18 percent lower levels of SERT in the brain’s hippocampus compared to healthy controls.
Paper: “Molecular imaging of serotonin degeneration in mild cognitive impairment”
Reprinted from materials provided by Johns Hopkins University.