Chronic Mild Stress (CMS) Protocol

CMS regimen was employed based upon established protocols shown to induce anhedonia in mice⁷². Social isolation of mice is a mild stressor when the animals can still hear and smell each other from within the same room. Control mice remained in their original social housing groups (5 mice per cage), whereas stressed animals were placed in solitary housing. In a separate room, CMS mice were exposed to a randomly selected daily stressor, six days per week for four weeks: mild hunger (8 day cycle hrs., no food, water ad libitum), night illumination (200 lux light during the 12-hour colony dark cycle), cage tilt (8 day cycle hrs., cage angle of 30°), tail pinch (plastic clothespin was attached to the base of tail for 15 min.), forced swim (5 min., 20 cm deep, 25 °C water), cage crowding (8 day cycle hrs.: eight CMS mice were placed together in a standard cage), wet cage (250 ml water added to bedding for 8 day cycle hrs., then bedding was changed), empty cage (8 day cycle hrs, no bedding).