Provided herein methods of screening for potential antidepressant compounds effective to increase production of cellular CDP-diacylglycerol and synthesis of inositol phospholipid in depression-related areas of the brain. Also, provided are methods of diagnosing and treating depressive or mood disorders in a subject by administering these screened antidepressant compounds. Further provided is a method of determining the therapeutic efficacy of an antidepressant drug regimen by comparing the ratio of CDP-diacylglycerol/inositol phosphate after treatment to a basal ratio in a subject.