Presynaptic serotonergic dysfunction in patients with Alzheimer's disease

Area of Science:

• Neuroscience
• Neuropathology
• Biochemistry

Background:

• Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive decline.
• Serotonergic system dysfunction has been implicated in the pathophysiology of AD.

Purpose of the Study:

• To investigate the integrity of presynaptic serotonergic nerve endings in the neocortex of Alzheimer's disease patients.
• To correlate serotonergic markers with neuropathological features and dementia severity in AD.

Main Methods:

• Assay of 5-hydroxytryptamine (serotonin) and 5-hydroxyindoleacetic acid concentrations.
• Measurement of serotonin uptake and K+-stimulated serotonin release in neocortical biopsy samples.
• Correlation analysis with dementia ratings, cholinergic markers, plaque/neurone loss, neurofibrillary tangles, and glucose oxidation.

Main Results:

• Reduced concentrations of serotonin and 5-hydroxyindoleacetic acid, impaired serotonin uptake, and decreased K+-stimulated serotonin release were observed in AD samples.
• These deficits were most pronounced in the temporal lobe, indicating significant serotonergic denervation.
• Serotonergic markers did not correlate with dementia severity, cholinergic indices, or plaque/neurone loss.
• Neurofibrillary tangle count and glucose oxidation correlated with 5-hydroxyindoleacetic acid levels.

Conclusions:

• Substantial loss of presynaptic serotonergic nerve endings occurs in the neocortex of Alzheimer's disease patients.
• The temporal lobe shows the most severe serotonergic denervation.
• Serotonergic deficits in AD are associated with neurofibrillary tangle pathology and neuronal metabolic activity.