The invention is directed to the use of a compound of formula I as defined herein, a pharmaceutically acceptable salt thereof; or a pharmaceutical composition containing a compound of formula I, in treating a mammal, including a human, for a psychiatric disorder or condition selected from the group consisting of depression, mood disorders, anxiety, schizophrenia, bipolar disorder (also referred to as manic-depressive disorder), addiction, cognitive impairment, Parkinson's and Alzheimer's diseases.