title: Quantification of 5-HT2A receptors in the human brain using [18F]altanserin-PET and the bolus/infusion approach.
abstract: The aim of the present study is to describe and validate a method for accurate quantification of 5-hydroxytryptamine (5-HT)(2A) receptors using [18F]altanserin-positron emission tomography (PET) and the bolus/infusion approach. A bolus/infusion ratio of 1.75 h aimed at attaining rapid steady state in blood and brain was predicted from previous bolus studies performed in our laboratory. The infusion schedule was tested in normal subjects (n = 10) using dynamic PET and frequent plasma sampling for 6 h. Steady state was attained in brain and plasma within 2 h, and time-activity curves remained constant for another 3 h. To represent free and nonspecifically bound [18F]altanserin and its radiolabeled metabolites only, cerebellum must show no displacement in 5-HT(2A) displacement studies. To validate this, saturating doses of cold ketanserin were administered and it was found that specific binding of [18F]altanserin decreased uniformly to the level of the cerebellum and no change in the cerebellar time-activity curve was found after ketanserin administration. A shorter experimental setup was tested in a second group (n = 20) including patients with neuropsychiatric disorders. Dynamic PET (five frames of 8 minutes each) and venous blood sampling at midscan time started 2 h after [18F]altanserin administration. The mean percentage rate of change per hour in the outcome parameter, DV(3)', was low (mean -0.3% h-1; range -7.3-7.2% h-1) and no correlation of DV(3)' versus time was demonstrated. It is concluded that 5-HT(2A) receptor studies can be conducted within 2 h of [18F]altanserin infusion, yielding reliable results.
authors.affiliation: Neurobiology Research Unit, Copenhagen University Hospital, Rigshospitalet, Denmark. pinborg@nru.dk
authors.forename: Lars H
authors.initials: LH
authors.lastname: Pinborg
authors.forename: Karen H
authors.initials: KH
authors.lastname: Adams
authors.forename: Claus
authors.initials: C
authors.lastname: Svarer
authors.forename: Søren
authors.initials: S
authors.lastname: Holm
authors.forename: Steen G
authors.initials: SG
authors.lastname: Hasselbalch
authors.forename: Steven
authors.initials: S
authors.lastname: Haugbøl
authors.forename: Jacob
authors.initials: J
authors.lastname: Madsen
authors.forename: Gitte M
authors.initials: GM
authors.lastname: Knudsen
mesh_terms: D000328:Adult; D000368:Aged; D001923:Brain Chemistry; D002531:Cerebellum / Q000737:chemistry; D005462:Fluorine Radioisotopes / Q000008:administration & dosage; D006801:Humans; D007267:Injections; D007650:Ketanserin / Q000008:administration & dosage / Q000031:analogs & derivatives*; D008875:Middle Aged; D011854:Radiochemistry; D011985:Receptors, Serotonin / Q000032:analysis*; D014055:Tomography, Emission-Computed
chemical_list: D005462:Fluorine Radioisotopes; D011985:Receptors, Serotonin; C071983:altanserin; D007650:Ketanserin