PROJECT SUMMARY Roughly 20% of women experience clinically significant anxiety, irritability, or depressive symptoms in the premenstrual (luteal) phase of the menstrual cycle. This includes premenstrual dysphoric disorder (PMDD), a severe affective disorder impacting millions of women worldwide. Despite this morbidity, research on PMDD’s pathophysiology lags behind that of other brain disorders. A potential contributor to PMDD’s pathophysiology is allopregnanolone (ALLO), a progesterone metabolite and powerful GABA-A receptor (GABA-A-R) modulator that fluctuates across the luteal phase. Importantly, rodent models of PMDD indicate impaired GABA-A-R plasticity in response to ALLO fluctuations. Building on this preclinical literature and clinical findings from the PI’s K23 (NIMH K23MH107831), the proposed research will test the hypothesis that rapid ALLO changes across the luteal phase, in interaction with suboptimal GABA-A-R receptor subunit reconfiguration, contribute to premenstrual mood symptoms. We will assess 67 women with regular menstrual cycles (33 controls, 34 with premenstrual dysphoric disorder (PMDD)) based on the gold standard Daily Record of Severity of Problems. We will capture two outcome measures: 1) We will measure plasma ALLO changes within subjects at multiple timepoints across the luteal phase using precise gas chromatography/mass spectrometry (GC/MS) methods. 2) We will use a novel biomarker, GABA-A-R subunit expression in peripheral blood mononuclear cell (PBMCs) measured via real-time polymerase chain reaction (RT-qPCR), to examine GABA-A-R subunit expression across the luteal phase. We hypothesize that controls and women with PMDD will differ in luteal phase decline in ALLO levels (e.g. controls will have a more gradual decline), and will differ in GABA-A-R subunit expression as ALLO levels decline. Combining these powerful methodologies will enable us to examine a mechanistic hypothesis about ALLO dynamics and GABA-A-R plasticity in women with premenstrual mood symptoms, in a prospective within-subject manner. The investigators bring complementary expertise; Dr. Hantsoo in prospectively studying women with PMDD, and Dr. Pinna in applying state-of-the-art methods to study the impact of ALLO on GABA-A-R function. This study represents a critical step in elucidating ALLO - GABA-A-R dynamics in this population, and will lead to an R01 that examines ALLO - GABA-A-R dynamics in women with PMDD when treated with selective serotonin reuptake inhibitors (SSRIs). Understanding PMDD’s pathophysiology may inform treatment development; only 60% of women with PMDD respond to the first-line treatment (SSRIs), and new GABA-modulating drugs are being developed (e.g. brexanolone and sepranolone, GABA-A modulating steroid antagonists). Before meaningful work is done in treatment development and personalized medicine in PMDD, mechanisms such as ALLO - GABA-A-R dynamics must be clarified.