 The depletion and post-depletion monitoring will occur daily for five 5 days, so depletion will begin on a Monday, unless circumstances require otherwise. Participants will be instructed to have a low-protein diet in the day prior to their second visit total content of less than 20g, and fast from midnight until their visit. Subjects will arrive at the clinic at 9AM on day 1 and commence depletion, under the supervision of the screening physician, who will monitor the subject over the next four days, including at 0- and 4-hours post-depletion. At 24 hours post-depletion, a blood sample will be drawn for analysis of amino acid and neurotransmitter levels 5mL. Subjects will not be hospitalized during their participation, unless it is deemed necessary by clinicians judgment, but will be given 24-hour contact information for the attending physician. The same physician will see a given subject for the duration of their participation, and all raters involved in this study will have previously demonstrated an inter-rater reliability of 0.85 for all scales. At all visits 1-5, subjects will have mood assessed using a Visual Analog Scale, for self-rating, and by the Hamilton Rating-Scale for Depression. Concomitant medications will also be recorded. 