 Patients with major depressive disorder MDD commonly have many gastrointestinal complaints. Gastrointestinal pain is classified into 2 categories: visceral and somatic pain. The main aim of this study is to compare somatic and visceral sensitivity between healthy people and pateints with MDD. These two sensitivities will be assessed by the 2 following tests: standardized rectal distension and Transdermal transcutaneous electric nerve stimulation. Thereafter, patients with MDD will be randomly allocated to escitalopram or reboxetine. After 6 weeks of treatment, somatic and visceral sensitivity will be reassessed. 