Anesthesia protocol
The subjects abstained from the use of alcohol and any medications for at least 48 h and from the use of caffeine-containing products for 10–12 h and fasted overnight before the experiments. Two forearm veins were cannulated for administration of study treatments and the PET radiotracer. The left radial artery was cannulated to obtain blood samples for drug concentration measurements and kinetic modeling of the PET radiotracer. The intravenous anesthetic agents, propofol (Propofol Lipuro 10 mg/ml, B. Braun), dexmedetomidine (Dexdor 100 μg/ml, Orion Pharma) and S-ketamine (Ketanest-S 25 mg/ml, Pfizer) were administered using target controlled infusion (TCI) with previously described pharmacokinetic parameters (