Impact of GABA-Enhancing Agents on Cortical GABA Concentrations Across the Menstrual Cycle in Women

Inclusion Criteria: * Women ages 18-45 and able to give voluntary written informed consent; * Regular menstrual periods of 24-35 days in length; * Body mass index 18.5 to 30 kg/m2; * No past or present DSM-IV psychiatric or substance dependence diagnosis by structured diagnostic interview (SCID-NP); no substance abuse history within the previous 2 years; * Absence of mood symptoms across the menstrual cycle during one month of prospective daily ratings with the Daily Record of Severity of Problems (DRSP); the DRSP is based on the DSM-IV research criteria for premenstrual dysphoric disorder (PMDD) and has been used in numerous studies to confirm the presence or absence of significant premenstrual mood and behavioral difficulties; * Must be willing and able to participate in at least three of the four challenge paradigms. Exclusion Criteria: * Medical, neurologic or cerebrovascular disorder (CVA, seizure disorder, etc.); * Family history of first degree relative with an Axis I psychiatric or substance dependence disorder (excepting alcohol and nicotine) (per subject report); * Current treatment with psychoactive medication; * Diabetes controlled by means other than diet; * Use of steroid contraceptives (any method involving hormones) within the previous 4 months; * Habitual consumption of more than 7 alcoholic drinks per week or more than 2 drinks on any particular occasion; must be willing to abstain from alcohol consumption for 48 hours prior to each 1H-MRS scan; * Implanted metallic devices.