A review of the literature on neuroimaging of serotoninergic function in Alzheimer's disease and related disorders

Behavioural and psychological disorders are frequent not only in frontotemporal dementia (FTD), but also in Alzheimer's disease (AD), and many of them are related to serotoninergic dysfunction. In vitro biochemical measurements on brain samples show both pre- and post-synaptic impaired brain serotoninergic function in degenerative dementia, sometimes related to hyperactivity or aggressive behaviour. To date, few studies have explored in vivo 5HT2A and 5HT1A brain receptors in AD and FTD. They suggest that brain cells are lost in the associative cortices (5HT2A) and hippocampus (5HT1A) of AD patients, and in the medial prefrontal and orbitofrontal cortices of FTD subjects (5HT2A). Apart from reflecting a loss of local neurons, the meaning of the decrease in 5HT receptors is not yet clear and larger populations are required to establish relationships with clinical symptoms such as dementia severity and search for possible consequences for patients' behavioural and affective status.