Depression is both a debilitating psychological disorder and a condition that affects an individual's physical well-being. Depression is a recognized risk factor for heart disease. Research has demonstrated that depression predisposes an individual to myocardial infarction, sudden death, atherosclerosis, thrombosis and arrhythmias. While the behavioral and cognitive aspects of depression have been studied extensively, there has been much less research investigating the mechanisms responsible for the physiological consequences of mood disorders. Exposure of rodents to a series of chronic mild stressors (CMS) generates key behavioral characteristics of human depression that are observable and quantifiable. The CMS model of experimentally-induced depression (ID) mimics the reduced responsiveness to pleasurable stimuli (anhedonia)which is a pivotal diagnostic criterion seen in depression. In the CMSdD model, anhedonia is induced by presenting mild unpredictable stressors (e.g., paired housing, stroboscopic illumination, white noise) of varying durations. In rats,anhedonia is operationally defined as a decrease in responding for a previously demonstrated reinforcer (reward). Recently, we have begun to characterize cardiovascular function in rats with CMS-ID. We have found that rats exposed to CMS for 4 weeks showed anhedonia along with cardiovascular alterations. Similar to patients with depression and with heart failure,CMSgD rats had elevated resting heart rates and reduced heart rate variability. In addition, rats exposed to CMS have increased susceptibility to experimentally-induced premature ventricular contractions. In other studies investigating the behavioral consequences of heart failure, we have found evidence of anhedonia (i.e., experimental depression) in rats with experimental myocardial infarction. The proposed research program will extend our characterization of the cardiovascular changes that accompany experimentally-induced depression and investigate the role of brain serotonergic mechanisms that are hypothesized to be common in the mediation of cardiovascular alterations that accompany both experimental depression and experimental heart failure.
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