MRI shows lower brain serotonin levels linked to dementia, according to a study published in Neurobiology of Disease.
Researchers from Johns Hopkins University School of Medicine in Baltimore, MD, performed a small study (28 participants with mild cognitive impairment and 28 controls) to measure the serotonin transporter in vivo in mild cognitive impairment and healthy controls.
The participants with cognitive impairments were a median age of 66.6 (16 males) and the controls were a median age of 66.2 (15 males). All underwent MR imaging for measurement of grey matter volumes and high-resolution PET with well-established radiotracers for the serotonin transporter and regional cerebral blood flow. Beta-amyloid imaging was performed to evaluate, in combination with the neuropsychological testing, the California Verbal Learning Test and the Brief Visuospatial Memory Test.
The researchers tested the following hypotheses:
1) The serotonin transporter would be lower in mild cognitive impairment compared to controls in cortical and limbic regions
2) In mild cognitive impairment relative to controls, the serotonin transporter would be lower to a greater extent and observed in a more widespread pattern than lower grey matter volumes or lower regional cerebral blood flow
3) Lower cortical and limbic serotonin transporters would be correlated with greater deficits in auditory-verbal and visual-spatial memory in mild cognitive impairment, not in controls
The results showed reduced serotonin transporter availability in the participants with mild cognitive impairment compared to controls in cortical and limbic areas typically affected by Alzheimer's disease pathology, as well as in sensory and motor areas, striatum, and thalamus that are relatively spared in Alzheimer's disease. The reduction of the serotonin transporter in mild cognitive impairment was greater than grey matter atrophy or reductions in regional cerebral blood flow compared to controls. Lower cortical serotonin transporters were associated with worse performance on tests of auditory-verbal and visual-spatial memory in mild cognitive impairment, not in controls.
In the California Verbal Learning Test, the healthy participants had an average score of 55.8, whereas those with mild cognitive impairment scored an average of 40.5 on a scale of 0 to 80 (80 reflected best memory) and the controls scored an average of 36 (36 being the top score) in the Brief Visuospatial Memory Test, while participants with mild cognitive impairment scored an average of 20.0.
"Now that we have more evidence that serotonin is a chemical that appears affected early in cognitive decline, we suspect that increasing serotonin function in the brain could prevent memory loss from getting worse and slow disease progression," coauthor Gwenn Smith, PhD, professor of psychiatry and behavioral sciences and director of geriatric psychiatry and neuropsychiatry at Johns Hopkins University School of Medicine, said in a release.