<qa>  What is a serious syndrome that resembles a major depressive episode?Postpartum depression PPD is a serious syndrome which resembles a major depressive episode and occurs in 10-20 of all mothers in the year following delivery. The etiology of PPD involves psychological factors, environmental factors such as stress and sleep deprivation, biological factors including hormonal changes, and social factors. Women with histories of major depression MDD are at an increased risk for PPD and recurrent PPD with subsequent pregnancies. No consistent hormonal abnormalities have been found in women with PPD and, instead, they may be sensitive to the normal changes in hormone levels during the postpartum time. One possible genetic vulnerability to depression, and in particular PPD, is the brain-derived neurotrophic factor BDNF gene. BDNF is an important member of the neurotrophin family and is known to affect neuronal outgrowth, differentiation, synaptic connectivity and neuronal repair for a broad range of neuronal cell types including serotonergic neurons. In humans, serum BDNF levels have been shown to be significantly lower in patients with depression, including women . Interestingly, estrogen has been shown to upregulate the expression of the BDNF gene in animals, suggesting that BDNF could be a critical link for women who have hormonally related depressive symptoms. In addition, serotonin-selective reuptake inhibitors SSRI used to treat depression are known to upregulate the expression of BDNF in the brain. Interestingly, links between depression, perturbed energy metabolism and BDNF signaling have recently been elucidated. In the present study, NIA investigators will measure levels of BDNF and reproductive and energy-regulating hormones in serum samples from subjects enrolled in Dr. Jennifer Payne s study of PPD. 