FAILURE TO CHANGE EXPLORATION OR SACCHARIN PREFERENCE IN RATS EXPOSEDTO CHRONIC MILD STRESS

Chronic mild stress (CMS) exposes animals to unpredictable stressors. Reduced consumption of sucrose or saccharin solutions by CMS rats has been used as a putative measure of anhedonia, typical of depression. O ur objective was to determine whether saccharin consumption and prefer ence and suppression of exploratory and rearing behaviors in the open field were reliable indicators of CMS-induced behavioral depression. I n Experiment 1, male Wistar rats subjected to 6 weeks of CMS consumed significantly less food and gained less weight than controls. CMS did not effect saccharin intake, or preference, measured in a two-bottle t est with water. CMS rats exposed to a novel open field showed increase d exploration and rearing. In a second test, performed immediately aft er a novel stress of restraint, there were no differences in explorato ry or rearing behavior of CMS and control rats. In Experiment 2, CMS w as reduced to 3 weeks and rats were single or group housed in their ho me cages. Open field activity of CMS rats was similar to that in Exper iment 1. Saccharin preference of CMS rats was significantly suppressed when tested after 24 hours of water deprivation, but was not differen t from controls after 5 hours of water deprivation. In the final exper iment Sprague Dawley rats behaved the same as Wistar rats in the CIMS paradigm. Therefore, the CMS protocol used in these experiments did no t induce behaviors indicative of depression but did cause a mild anore xia and weight loss. Saccharin intake of CMS rats was dependent upon t heir dehydration state and could not be attributed to stress-induced a nhedonia. (C) 1998 Elsevier Science Inc.