The aldehyde form of serotonin promotes formation of alpha-synuclein oligomers and serotonin blocks formation of amyloid from alpha-synuclein.
Whether these are clinically relevant remains to be seen.
The serotonin aldehyde, 5-HIAL, oligomerizes alpha-synuclein. - PubMed - NCBI
The neurotransmitter serotonin interrupts α-synuclein amyloid maturation. - PubMed - NCBI