The purpose of the study proposed is to investigate the role of neurosteroids and GABA in the pathophysiology and treatment of premenstrual dysphoric disorder (PMDD) by 1) measuring cortical gama-aminobutyric acid levels (GABA levels) using nuclear magnetic resonance spectroscopy (MRS) during the follicular and mid-luteal phases of the menstrual cycle pre and post treatment with the selective serotonin reuptake inhibitor (SSRI) fluoxetine (Prozac®, Sarafem®), and 2) correlating cerebrospinal fluid (CSF) and plasma GABA and neurosteroid levels with cortical GABA levels at these same time points. Neurosteroids to be measured include allopregnanolone, pregnenolone, and pregnenolone sulfate. Findings from women with PMDD will be compared to those of healthy subjects.