• Measured at Weeks 1, 4, and 6: Catecholamine metabolism and blood cell adenylate cyclase activity
  
• Score on the 21-item Hamilton Depression Rating Scale
  

MDD is a serious mental illness that can interfere with a person’s ability to eat, sleep, work, and enjoy activities that were once pleasurable. It is characterized by several symptoms, including as the following: persistent sad, anxious, or "empty" mood; feelings of hopelessness or pessimism; and feelings of guilt, worthlessness, or helplessness. The receptor-G protein-adenylate cyclase enzyme complex (AC enzyme complex) is a major cell signaling system in the brain, blood, and other tissues in the body. Changes in this signaling system among blood cells have been observed in people with major depressive disorder. Research has shown that treatment with the benzodiazepine alprazolam corrects the signaling problem, and thereby improves symptoms of MDD. This study will determine whether impairments in the AC enzyme complex exist among depressed individuals. This study will also evaluate the effectiveness of desipramine, an antidepressant, in improving blood cell signaling, and thereby decreasing symptoms of depression in people with major depressive disorder.

Both healthy and depressed participants will be recruited for this study. All depressed participants in this study will first be assessed for depression severity using the Hamilton Depression Rating Scale. If eligible for the study, participants will be examined to determine AC enzyme complex functioning in both platelets and mononuclear leukocytes. A cohort of the depressed participants will be treated with desipramine. They will be examined to determine the drug’s effect on AC enzyme complex functioning, as well as its effect on MDD symptoms, at Weeks 1, 4, and 6.