Further in vivo characterization of [11C]-(+)-PHNO uptake into a retina-like region of interest in humans

The neurotransmitter dopamine is present in the retina and is involved in several modulatory functions. Unlike in rodents, dopamine D-3 receptors are expressed in the retina of humans. Recently, uptake of the D-3 receptor-preferring radiotracer [C-11]-(+)-PHNO has been observed in a retina-like region of interest (ROI) in humans. Here, we attempted to quantify [C-11]-(+)-PHNO uptake into this ROI using an independent sample, employing an extended scan acquisition time (120 min) and arterial kinetic modeling. Data from 14 healthy controls were analyzed (Mean Age: 38.41 +/- 9.55, 3 female), 8 of which provided arterial line input function data (Mean Age: 41.07 +/- 7.82, 3 female). Using Ichise's multilinear analysis (MA1) method, it was possible to quantify the volume of distribution (V-T) of [C-11]-(+)-PHNO in this retina-like region (Mean V-T = 13.56 +/- 3.52; Mean chi(2) = 2.08 +/- 2.20). Notably, the shape of the time activity curve resembled closely that of the globus pallidus. Moreover, the V-T values in the retina correlated well with binding potential (BPND) values calculated using the simplified reference tissue model (Mean BPND = 2.11 +/- .94; Mean chi(2) = 5.76 +/- 2.56), employing the cerebellum as the reference region (r = .76, r(2) = .58). In summary, we provide evidence that the in vivo uptake of [C-11]-(+)-PHNO into a retina-like ROI in humans can be quantified using both arterial blood sampling (V-T) and simplified reference tissue methods (BPND).