Suppression of Sucrose Drinking by Chronic Mild Unpredictable Stress: a Methodological Analysis

Previous studies have demonstrated that chronic exposure of rats to a melange of ultra-mild stressors causes an antidepressant-reversible decrease in the intake of palatable weak sucrose solutions, as well as other evidence of insensitivity to rewards. In the present study, we analyzed some of the behavioral requirements for the suppression of consummatory behaviour by chronic mild stress. Rats exposed to our standard chronic mild stress protocol and tested following 20 h food and water deprivation showed a decrease in intake of 1% sucrose, but not of water or chow. The effect on sucrose intake was also present, but smaller, in non-deprived animals, and wa seen in both singly- and pair-housed animals. Experiments designed to identify the crucial elements of the stress procedure showed that one element, paired housing (in animals normally housed singly) was particularly potent. However, no one element was either necessary to cause the decrease in sucrose intake, or sufficient to maintain the impairment for longer than 4 weeks: Variety and frequency of microstressors appeared to be the essential features of procedures causing a prolonged anhedonia.