The main objective of this study is to characterize a range of brain activation symptoms associated with depression and response to treatment in midlife men and women with MDD, using MRI and functional MRI. Moreover, in the female sub-group, the investigators will examine whether these brain activation symptoms are related to menopausal symptoms (i.e., hot flashes and night sweats). Also, assessing brain activation before and after the treatment might help to uncover some mechanisms associated with the pathophysiology of depression and menopause.

Major Depressive Disorder (MDD) has been associated with morphological changes in the brain and changes in key brain areas. Studies have shown that antidepressant use may promote the normalization of these areas. Moreover, midlife men and women appear to be at greater risk for developing major depressive episodes. In women, this period of life has been associated with significant functional impairment due to the presence/severity of vasomotor symptoms (hot flashes, night sweats), cognitive complaints, and poorer quality of life. Desvenlafaxine succinate (DVS) has been developed for the treatment of MDD. To date, the effects of DVS on brain structure and functioning in midlife men and women with MDD, as well as on depression related to menopause, has not been explored. The present study aims to investigate the effects of DVS on brain structure and functioning when used for the treatment of a major depressive episode in midlife men and women, using MRI and functional MRI. In addition, the investigators will examine whether the impact of treatment with DVS on vasomotor symptoms, cognition, and quality of life modulate the putative changes in brain structure and functioning.

Inclusion Criteria:

• men and women, aged 40-60 years
• diagnosis of MDD
• for women, perimenopausal or postmenopausal

Exclusion Criteria:

• other DSM-IV axis I diagnosis other than MDD
• using psychotropic medications
• suicidal ideation, homicidal ideation, or psychotic symptoms
• presence of laboratory abnormalities at baseline visit
• presence of heart disease, liver disease, kidney disease, pulmonary disease, blood or bleeding disease, thyroid disease, GI disease, seizure or epilepsy, head injury, cancer, uterine fibroids or endometriosis, gynecologic surgeries (except caesarian sections), electroconvulsive therapies in the past 3 months, HIV+/AIDS
• in addition (for women): use of hormone replacement therapies, menstrual dysfunction, pregnancy or breastfeeding