[en] To further validate its use in positron emission tomography (PET), we studied the binding of [¹⁸F]altanserin, a specific 5HT₂ radioligand, in the rat brain using in vivo autoradiography. Distribution of [¹⁸F]altanserin binding was comparable to the in vitro mapping of 5HT₂ receptors reported in the literature. Selective displacers were used to test the reversibility and the selectivity of this radioligand. Specific binding of [¹⁸F]altanserin in the rat frontal cortex was quantified by direct counting with an electronic imaging system and by quantification on digitalized autoradiograms. Close results of about 30 pmol/g were obtained with both methods. Our data confirmed that [¹⁸F]altanserin is a valid tracer for 5HT₅ receptors binding studies

[en] Serotoninergic type 2 (5HT₂) receptors have been implicated in the regulation of many brain functions in humans and may play a role in several neurological and psychiatric diseases. Fluorine-18 altanserin has been proposed as a new radiotracer for the study of 5HT₂ receptors by PET because of its high affinity for 5HT₂ receptors (Ki: 0.13 nM) and its good specificity in in vitro studies. Dynamic PET studies were carried out in 12 healthy volunteers after intravenous injection of 0.1 mCi/kg [¹⁸F] altanserin. Ninety minutes after injection, we observed mainly cortical binding. Basal ganglia and cerebellum showed very low uptake and the frontal cortex to cerebellum ratio was about 3. To evaluate the quantitative distribution of this ligand in the brain, we used two different methods of data analysis: a four-compartment model was used to achieve quantitative evaluation of rate constants (K₁ and k₂ through k₆) by non-linear regression, and a multiple-time graphical analysis technique for reversible binding was employed for the measurement of k₁/k₂ and k₃/k₄ ratios. Using both methods, we found significant differences in binding capacity (estimated by k₃/k₄ = B_max/K_d) between regions, the values increasing as follows: occipital, limbic, parietal, frontal and temporal cortex. After correction of values obtained by the graphical method for the existence of non-specific binding, results generated by the two methods were consistent. (orig.)