Behavioral and cardiovascular changes in the chronic mild stress model of depression

Depression is a multifaceted psychological disorder that involves changes in behavior, neuroendocrine function, and physiological responses. The present study investigated multiple behavioral and cardiovascular consequences in the chronic mild stress (CMS) rodent model of depression. Rats were exposed to 4 weeks of CMS followed by 4 weeks of a stress-free recovery period. Sucrose intake, a measure of anhedonia, and spontaneous locomotor activity were measured weekly throughout the study, and cardiovascular function tests were conducted at the completion of the protocol. The results indicate that CMS results in anhedonia and reduced locomotor activity, as well as elevated heart rate (HR), reduced HR variability, and elevated sympathetic cardiac tone. The behavioral effects of CMS recovered to baseline (prestress) levels during the recovery period; however, cardiovascular changes were observed following the recovery of sucrose intake and activity levels. The present findings suggest that behavioral changes that are indicative of anhedonia and locomotor alterations associated with depression are dissociable from long-term cardiovascular changes induced by CMS.