Major depressive disorder is 1.5 to 3 times more common among first-degree biological relatives (immediate family) of persons with this disorder. The reported incidence of depression is 3 times higher in women than in men. Suicide ideation and attempts are risk factors. ‘Candidate gene’ investigations are being pursued. Serotonin transporter mutations are linked to mood and many other disorders. The range of drugs available to treat depression called Selective Serotonin Reuptake Inhibitors (SSRI) help only about 50% of major depressive patients. The 2 to 3 weeks delay in mood-elevating and current psychotropic drugs taking effect presents a continuing mystery to neuroscientists. When these adaptations occur in the brain, its nature at the molecular level has yet to be identified with certainty as the neural circuitry for mood encompasses several brain areas (see diagram & descriptive info). Normal bereavement can last up to 2 years, and may constitute a stressor that can precipitate a major depressive episode in vulnerable individuals. Recurrence of this disorder is high.
Structural and functional brain abnormalities in patients with major depressive disorder with volume and activity increment and reduction.
Perfrontal Cortex/Lobe & Cingulate: cognitive function, attention.
Ventral Hippocampus: Cognitive function, memory.
Ventral Striatum: Reward, aversion.
Hypothalamus: regulates sleep, appetite, energy, sex.
Amygdala: mediates responses to emotional stimuli, including fear.
Hypothalamic-pituitary-adrenal axis that controls reactions to stress and regulates the immune system.
Ventral Tegmental Area: sends dopaminergic projections to other areas, important in cognition, motivation, intense emotions relating to love and several psychiatric disorders.
Dorsal Raphe Nuclei: send serotonergic input to other areas, controls physiological functions, learning, memory, and affect.
Locus Coeruleus: sends noradrenergic input to other areas, involved with physiological responses to stress and panic.