Background and aims: The central serotonergic (5-HT) system is closely involved in regulating various mental functions associated with mood, anxiety, impulsive behavior etc. To date, several reports have addressed the comparison between pre- and postsynaptic functions of 5-HT (1, 2); however, these studies are limited in their applicability because of their small sample size. The aim of this study was to investigate the intraindividual relationship between 5-HTT and 5-HT1A receptors using PET in a relatively large group of normal male subjects.Methods: Dynamic PET scans were performed on 23 young, healthy males with both [C-11]DASB and [C-11]WAY-100635 to measure the binding of 5-HTT and 5-HT1A receptors, respectively. A 2-parameter multilinear reference tissue model and a reference tissue model were used to calculate the binding potential (BPND) of [C-11]DASB and [C-11]WAY-100635, respectively, on a voxel-by-voxel basis, with the cerebellum as the reference region. All PET images were anatomically standardized to the template magnetic resonance image and smoothed with an 8-mm Gaussian filter using SPM2. Furthermore, the volumes-of-interest (VOIs), namely, the raphe nucleus, thalamus, striatum, parahippocampal gyrus, insula, temporal cortex, base of the frontal cortex, and the convexity of the frontal cortex were manually traced on the standardized and smoothed BPND images. Pearson\u27s coefficient correlation was used to compare the bindings of both the tracers in the same VOIs; corrections for multiple comparisons among VOIs were not performed.Results: The BPND values of each VOI are presented in Table (mean +/- SD).[tab_01] Pearson\u27s correlation coefficient indicated significant inverse correlations between BPND of [C-11]DASB and that of [C-11]WAY-100635 in the insula (r = -0.46, p = 0.028), base side of the frontal cortex (r = -0.47, p = 0.023), and the convex side of the frontal cortex (r = -0.46, p = 0.029). No significant correlation was observed in other regions.Conclusions: The distribution of 5-HTT and 5-HT1A receptors in the brain was consistent with the findings of post-mortem studies. In addition, we found inverse correlations between BPND values of 5-HTT and 5-HT1A in the insula and frontal cortex. These relationships might indicate a complementary nature between 5-HTT and 5-HT1A functions in such regions. Further investigations are required to elucidate the relationship between the activity of the pre- and postsynaptic serotonergic system in relation to mental functions.Reference:1) Lundberg et al. Psychopharmacology, 195, 425-433, 20072) Frey et al. Neuroimage, 42, 850-857, 2008Brain \u2709 & Brain PET \u270
