The main purpose of this study is to model tissue specific kinetics of [11C]Yohimbine in
healthy male participants by positron emission tomography (PET) and the appropriate arterial
input function (part A) ; to determine the reproducibility of measures (classical test-retest
study, part B1) and to measure the blocking of [11C]Yohimbine uptake in the brain following
single oral dose administration of clonidine (part B2).