Changes in serotonin-2 receptors have been demonstrated in brain autopsy 
material from patients with various neurodegenerative and affective disorders. 
It would be desirable to locate a ligand for the study of these receptors in 
vivo with positron emission tomography (PET). Altanserin is a 
4-benzoylpiperidine derivative with a high affinity and selectivity for S2 
receptors in vitro. Dynamic PET studies were carried out in nine normal 
volunteers with high-specific activity (376-1,680 mCi/mumol) [18F]altanserin. 
Arterial blood samples were obtained and the plasma time-activity curves were 
corrected for the presence of labeled metabolites. Thirty minutes after 
injection, selective retention of the radioligand was observed in cortical 
areas, while the cerebellum, caudate, and thalamus had low radioactivity levels. 
Specific binding reached a plateau between 30 and 65 min postinjection at 1.8% 
of the injected dose/L of brain and then decreased, indicating the reversibility 
of the binding. The total/nonspecific binding ratio reached 2.6 for times 
between 50 and 70 min postinjection. The graphical analysis proposed by Logan et 
al. allowed us to estimate the binding potential (Bmax/KD). Pretreatment with 
ketanserin was given to three volunteers and brain activity remained uniformly 
low. An additional study in one volunteer showed that [18F]altanserin can be 
displaced from the receptors by large doses of ketanserin. At the end of the 
study, unchanged altanserin was 57% of the total plasma activity. These results 
suggest that [18F]altanserin is selective for S2 receptors in vivo as it is in 
vitro. They indicate that [18F]altanserin is suitable for imaging and 
quantifying S2 receptors with PET in humans.