Abstract
Immune responses have been mostly studied at a specific time in anuran species. However, time-changes related to immunomodulation associated with glucocorticoid (GC) alterations following stressors and GC treatment are complex. The present study describes time-related changes in immune response and corticosterone (CORT) plasma levels following restraint challenge, short, mid and long-term captivity, and CORT exogenous administration by transdermal application (TA) in Rhinella ornata toads. We observed increased neutrophil: lymphocyte ratios after restraint challenge and CORT TA, without changes following short and mid-term captivity. Plasma bacterial killing ability was sustained in all treatments, except long-term captivity, with decreased values after 90 days under such conditions. Phagocytic activity of peritoneal cells increased after mid-term captivity, and the phytohemagglutinin swelling response was impaired in those animals treated with CORT TA for 20 consecutive days. Plasma CORT levels increased or were sustained after restraint challenge (depending on initial values), decreased following mid and long-term captivity (for those animals showing high CORT in the field) and increased after 20 days of CORT TA. By performing assessments of time-changes in immune processes and CORT plasma levels in R. ornata, we demonstrate immuno-enhancing effects following restraint, short and mid-term stressors, while long-term stressors and CORT TA promoted immunosuppression in these toads.
Highlights
Stress-induced immunomodulation is complex and frequently associated with immune suppressive effects
CORT plasma levels after CORT transdermal application (TA) were extremely high in the experimental group (348 ± 54ng/ml, mean ± standard error), high CORT levels (282 ± 52ng/ml, mean ± standard error) were reported for this same species following severe dehydration [13], evidencing these animals are physiologically able to reach such high circulating CORT levels
Different time-related trajectories for CORT plasma levels and immune parameters were described in R. ornata toads following stressors and CORT TA
Summary
Stress-induced immunomodulation is complex and frequently associated with immune suppressive effects. While long-term stress usually results in immune suppressive effects, short-term stress can enhance the immune response [2]. Glucocorticoids (GCs), one of the major mediators of the stress response, influence immune cell redistribution and immune function in several vertebrates, including amphibians [3,4,5,6,7]. Leukocyte redistribution is associated with wound healing by increasing immune responsiveness in body compartments requiring immune protection [3,8,9]. As a result, this leukocyte redistribution is reflected as an increase in blood
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