A dysfunction of multiple neurotransmitter systems is assumed as a neurochemical 
basis of the akinetic-rigid syndrome of progressive supranuclear palsy (PSP). In 
vitro studies have produced conflicting results on the serotoninergic system in 
PSP. We, therefore, studied the binding potential of the serotonin 2A (5-HT(2A)) 
receptor ligand [18F]altanserin in 8 patients with clinically probable PSP and 
13 healthy controls using positron emission tomography. We found an 
up-regulation of 5-HT(2A) receptors in the substantia nigra and, to a lower 
degree, in the striatum, while neocortical 5- HT(2A) receptor densities showed 
no changes upon partial-volume correction. Nigral and striatal receptor changes 
were significantly correlated with patients' scores of motor dysfunction (UPDRS 
III, PSP-rating scale) pointing to a functional relevance of the described 
findings.