Early Blood Profile of C57BL/6 Mice Exposed to Chronic Unpredictable Stress

Abstract

Physiological responses to psychological stressors are protective in acute fight or flight situations; however, there is increasing evidence suggesting the detrimental impact of chronic psychological stress on disease. Chronic stress has been associated with inflammation, poor prognosis, increased morbidity, and poor outcome in many diseases including atherosclerosis, cancer, and pulmonary disease. Given the systemic impact of stress, and the role of the hematopoietic system as a rapid responder to homeostatic insults, we hypothesized that early blood profile changes and biochemical alterations could be detected in a model of chronic stress. To test this hypothesis, a variation of the chronic unpredictable stress (CUS) model was employed. Following 10 days of CUS, C57BL/6 mice exhibited a chronic-stress-associated corticosterone profile. Complete blood count (CBC) revealed mild normochromic, normocytic anemia, and reduced monocyte and lymphocyte count. Serum analysis demonstrated hypoferremia with unchanged total iron binding capacity and serum ferritin levels. These findings are consistent with clinical diagnostic parameters for anemia of chronic disease and indicate that CUS results in significant changes in blood and serum biochemical profile in C57BL/6 mice. These studies identify early changes in blood parameters in response to CUS and identify hematopoietic and biochemical alterations that are often associated with increased morbidity in patients experiencing chronic-stress-associated mental health disease.

Keywords: C57BL/6; anemia; blood; chronic unpredictable stress; disease; iron; physiological response; psychological stress.

Figure 1

CUS response and CBC analysis. Chronic stress response was measured in animals following 1 day and 10 days of CUS procedures and compared to nonstressed control animals. (A) Body weight was measured at 1 day and 10 days following CUS, demonstrating a significant effect of stress [F(1,36) = 5.590], but there was no significant interaction between time and stress [F(1,36) = 0.259] and there was no significant effect of time [F(1,36) = 0.259, p = 0.614]. (B) Serum corticosterone levels were significantly elevated following acute stress (1 day), [t(14) = 2.915, *p = 0.011]. (C) Serum corticosterone levels were significantly decreased following 10 days of CUS procedures [t(20) = 2.431, *p = 0.025]. CBC comparison including (D) monocyte count (MO) [t(37) = 2.007, p = 0.052], (E) lymphocyte count (LY) [t(37) = 3.032, **p = 0.004], (F) neutrophil count (K/µl), and (G) neutrophil (K/µl)-to-lymphocyte (K/µl) ratio (NLR) [U = 351, p = 0.380; F(19,18) = 25.60, *p < 0.001] in control versus CUS cohort animals showed hematopoietic alterations as a result of CUS procedures. (H) Red blood cell (RBC) count (U = 116.5, *p = 0.038), (I) hemoglobin (U = 113, *p = 0.030), and (J) hematocrit were also reduced in CUS versus control cohort (U = 84.5, **p = 0.002). (*p ≤ 0.05, **p ≤ 0.01).

Figure 2

Serum analysis. (A) Iron saturation [t(18) = 2.753, *p = 0.013] and (B) serum iron concentration were decreased in CUS versus control cohort [t(13.387) = 3.645, **p = 0.003]. (C) Total iron binding capacity was not significantly altered [t(18) = 0.625, p = 0.540]. (D) Serum ferritin levels showed a nonsignificant increase in CUS versus control cohort [t(15) = 1.104, p = 0.287]. (*p ≤ 0.05, **p ≤ 0.01).