70 minutes after the start of clamp and 40 minutes after the application of nasal sprays the positron emission tomography (PET) scanning is started with the injection of glucose-analogue tracer labeled with positron-emitting fluorine-18 ([18F]-fluorodeoxyglucose, [18F]-FDG). PET/CT, GE DiscoveryTM ST System (General Electric Medical Systems, Milwaukee, WI, USA) with final resolution of 3.75 mm in PET images is used. All data will be corrected for dead-time, decay and measured photon attenuation. Dynamic PET-scans will be reconstructed with iterative reconstruction method. Radiotracer [18F]-FDG is produced in the PET Centre radiochemistry laboratory. Plasma radioactivity is measured with an automatic gamma counter by a medical technologist in the laboratory of the Turku PET Centre (Wizard 1480 3", Wallac, Turku, Finland).