A 31-year-old female is 3 weeks postpartum and presents with severe postpartum depression characterized by profound anhedonia, psychomotor retardation, inability to care for her infant, and passive thoughts of death. She has no prior psychiatric history. Her PHQ-9 score is 24. After discussing treatment options, the PMHNP refers the patient for brexanolone (Zulresso) infusion. Which of the following best describes the neurosteroid mechanism underlying brexanolone's rapid antidepressant effect in postpartum depression?