A test of reactive scope: Reducing reactive scope causes delayed wound healing

Abstract

Reactive scope predicts that all animals have an adaptive ability to respond to stressors in their environment, termed reactive homeostasis, and that only when an animal's response to stressful stimuli exceeds a certain threshold (homeostatic overload) will stress have pathological effects. While this framework has successfully helped interpret effects of stressors on wildlife, no study has designed an experiment to directly test this framework. This study was designed to expose house sparrows (Passer domesticus) to treatments that would result in varying ranges of reactive homeostasis during chronic stress, which based on the reactive scope model should cause birds with the lowest reactive homeostasis range to exhibit signs of pathology during a subsequent challenge. To modulate the reactive homeostasis range, we altered allostatic load of birds by exposing them to chronic stress while either elevating, blocking, or not manipulating corticosterone. After concluding chronic stress treatments, birds were exposed to the subsequent challenge of a superficial wound. Individuals treated with corticosterone during chronic stress (high allostatic load) experienced the most pathology, including both weight loss and slower wound healing. Unmanipulated birds (medium allostatic load) also experienced weight loss but had normal healing rates, while birds with blocked corticosterone (low allostatic load) had minimal weight loss and normal healing rates. Our results indicate that increased allostatic load reduces the reactive homeostasis range, thereby causing individuals to cross the homeostatic overload threshold sooner, and thus support the reactive scope framework.

House sparrows (Passer domesticus) adjusted hypothalamic‐pituitary‐adrenal axis negative feedback and perch hopping activities in response to a single repeated stimulus

“…The experimental design was based on prior chronic stress studies that indicated that the hormonal effects of chronic stress are typically initiated within 8–12 days (Awerman & Romero, ; Cyr et al, ; DuRant, Arciniega, Bauer, & Romero, ; Gormally, Wright‐Lichter, Reed, & Romero, ; Lattin & Romero, ). In several of these studies, birds were exposed to different stressors at four different unpredictable times throughout the day for up to 3 weeks.…”

Corticosterone rapidly suppresses innate immune activity in the House Sparrow (Passer domesticus)

“…A mitotane injection at the same dose as used here was previously shown to reduce plasma CORT for up to 10 days in adult male house sparrows (Breuner et al, 2000) and mitotane treatment inhibits CORT production in mammals (Chortis et al, 2012) and birds (Jonsson et al, 1994;DuRant et al, 2016). To counter potential problems of glucose mobilization resulting from low plasma CORT and to standardize the feeding regimen, we supplemented all birds, regardless of treatment, with fresh Nektar solution (13 g 100 ml −1 0.9% NaCl in water; Nekton, Germany) daily during the 10 days following injections of mitotane or vehicle.…”

Dietary fatty acids sex-specifically modulate guinea pig postnatal development via cortisol concentrations

“…Increased steroid hormone secretion rates during the postnatal development in SFA males were followed by a significantly higher mortality rate during adulthood. N-3 PUFA metabolites such as eicosanoids 46 and glucocorticoids in general 47 exert anti-inflammatory actions, whereas n-3 PUFA deficiencies and HPA-axis dysfunctions may profoundly impair the immune system and inflammatory responses 48 , 49 . Although the cause of deaths in SFA males was not investigated in this study, their highly increased cortisol concentrations may indicate a detrimental chronic stress state 49 , 50 .…”

“…N-3 PUFA metabolites such as eicosanoids 46 and glucocorticoids in general 47 exert anti-inflammatory actions, whereas n-3 PUFA deficiencies and HPA-axis dysfunctions may profoundly impair the immune system and inflammatory responses 48 , 49 . Although the cause of deaths in SFA males was not investigated in this study, their highly increased cortisol concentrations may indicate a detrimental chronic stress state 49 , 50 . This is usually accompanied by impaired glucocorticoid receptor sensitivity or even a resistance to cortisol, which is suggested to negatively affect HPA-axis responses to immune challenges, impair homeostasis, and increase the disease risk 49 , 51 , 52 .…”