Comparison of depressive behaviors induced by three stress paradigms in rats

Depression is a severe psychiatric disorder, which is a huge burden on both the individual and society as a whole. Neurobiological studies of depression on humans are limited by ethics. Animal models established by stressor stimulation are currently effective tools for the neurobiological study of depression. In this study, we comparatively analyzed behavioral heterogeneity, gender, and individual differences in animal models reflecting early life stress, adverse events in adulthood, or combined early life stress and stressful events in adulthood. Results demonstrated that these three different stressors induced dissimilar depressive behaviors. Maternal deprivation (MD) induced severe anhedonia. Chronic unpredictable stress (CUPS) induced the most severe decrease in desperation behavior, moderate anhedonia, and moderate loss of interest in exploration of the surroundings. Dural stress (DS) exposure caused the most severe decline in interest in exploring the surroundings. Male rats all exhibited some form of depressive behavior after they were exposed to MD, CUPS and DS. In contrast, no depressive performance was observed in female rats after they were exposed to MD, and the CUPS only decreased the total distance the rats crawled in the open field test. Rats exhibited more obvious individual differences in floating time than in the vertical activity, total distance and sucrose preference rate when experiencing stress. Our study suggests that different stressors may induce different depression subtypes and that the observed differences in the prevalence of depression between genders in the clinic may be due to effect of psychosocial factors which affects humans more strongly than rats. Our study also suggests that individual difference is more obvious in desperation behaviors than that in exploratory interest and anhedonia when the individual experienced stress.