[3H]PAROXETINE AND [3H]CITALOPRAM AS MARKERS OF THE HUMAN BRAIN 5-HT UPTAKE SITE - A COMPARISON STUDY

The binding of [H-3]paroxetine and [H-3]citalopram to the human brain serotonin (5-HT) uptake site has been characterized and compared. Our results reveal that the binding exclusively involved with the 5-HT uptake site is identical for both [H-3]ligands. The selective 5-HT uptake inhibitor citalopram displays the highest affinity for this uptake site, as compared with the affinities obtained for desipramine and norzimeldine, which is in accordance with their respective blockage of 5-HT uptake. Similar Bmax values were obtained for both radioligands in the brain regions studied, indicating their binding to the same presynaptic membrane protein. Together these findings suggest that both [H-3]paroxetine and [H-3]citalopram are good markers of the 5-HT transporter as both bind selectively and with high affinity to the serotonin uptake sites. However, the higher affinity of [H-3]paroxetine confirms that this compound is the best radioligand for the 5-HT uptake site available today.