Effect of Repeated Stress Exposures on the Blood Cytokine Profile in Rats with Different Behavioral Parameters

Changes in the blood cytokine profile were studied in rats with different behavioral patterns in the open-field test during chronic stress on the model of daily 4-h immobilization over 8 days. The level of proinflammatory cytokines IL-1α and IFNγ in behaviorally active and passive animals changed insignificantly under these experimental conditions. Repeated stress exposures were accompanied by a progressive decrease in the plasma level of IL-2 and IL-5 in passive rats; these changes were most pronounced on day 8 of the study. Active animals were characterized by a tendency toward reduction of IL-2 content, but significant decrease in IL-5 concentration on days 3 and 8 of restraint stress. Blood levels of IL-1β and IL-6 in rats remained practically unchanged after single immobilization, but progressively increased during further stress exposures and reached maximum on day 8 of stress. The content of the anti-inflammatory cytokine IL-4 in rats was constant, but blood concentration of IL-10 increased during repeated stress exposures. These changes were most pronounced on day 8 in passive animals and on days 3 and 8 of restraint stress in active animals. These data indicate that the direction of variations in the blood cytokine profile of rats under conditions of chronic stress depends on the baseline parameters of behavior and frequency of stress exposures.