Imaging of serotonin transporters with [123I]FP-CIT SPECT in the human hypothalamus

Background: Serotonergic neurons in the rodent hypothalamus are implicated in key neuroendocrine and metabolic functions, including circadian rhythmicity. However, the assessment of the serotonergic system in the human hypothalamus in vivo is difficult as delineation of the hypothalamus is cumbersome with conventional region-of-interest analysis. In the present study, we aimed to develop a method to visualize serotonin transporters (SERT) in the hypothalamus. Additionally, we tested the hypothesis that hypothalamic SERT binding ratios are different between patients with hypothalamic impairment (HI), pituitary insufficiency (PI), and control subjects (C). Methods: SERT availability was determined in 17 subjects (6 HI, 5 PI, and 6 healthy controls), 2 h after injection of I-123-N-omega-fluoropropyl-2 beta-carboxymethoxy-3 beta-(4-iodophenyl) nortropane ([I-123]FP-CIT), using single-photon emission computed tomography (performed on a brain-dedicated system) fused with individual magnetic resonance imaging (MRI) scans of the brain. The hypothalamus (representing specific SERT binding) and cerebellum (representing nonspecific binding) were manually delineated on each MRI to assess [I-123]FP-CIT binding and specific-to-nonspecific binding ratios. Results: In each healthy subject, [I-123]FP-CIT binding was higher in the hypothalamus than in the cerebellum, and the mean hypothalamic binding ratio of SERT was 0.29 +/- 0.23. We found no difference in hypothalamic binding ratios between HI, PI, and control subjects (HI 0.16 +/- 0.24, PI 0.45 +/- 0.39, C 0.29 +/- 0.23, p value 0.281). Conclusions: We were able to demonstrate SERT binding in the human hypothalamus However, we did not find altered hypothalamic SERT binding in patients with hypothalamic impairment.