Effects of corticosterone pellets on baseline and stress-induced corticosterone and corticosteroid-binding-globulin

Abstract

a b s t r a c tExogenous administration of glucocorticoids is a widely used and efficient tool to investigate the effects of elevated concentrations of these hormones in field studies. Because the effects of corticosterone are dose and duration-dependent, the exact course of plasma corticosterone levels after exogenous administration needs to be known. We tested the performance of self-degradable corticosterone pellets (implanted under the skin) in elevating plasma corticosterone levels. We monitored baseline (sampled within 3 min after capture) total corticosterone levels and investigated potential interactions with corticosteroid-binding-globulin (CBG) capacity and the endogenous corticosterone response to handling in Eurasian kestrel Falco tinnunculus and barn owl Tyto alba nestlings. Corticosterone pellets designed for a 7-day-release in rodents elevated circulating baseline total corticosterone during only 2-3 days compared to placebo-nestlings. Highest levels occurred 1-2 days after implantation and levels decreased strongly thereafter. CBG capacity was also increased, resulting in a smaller, but still significant, increase in baseline free corticosterone levels. The release of endogenous corticosterone as a response to handling was strong in placebo-nestlings, but absent 2 and 8 days after corticosterone pellet implantation. This indicates a potential shut-down of the hypothalamo-pituitary-adrenal axis after the 2-3 days of elevated baseline corticosterone levels. 20 days after pellet implantation, the endogenous corticosterone response to handling of nestlings implanted with corticosterone pellets attained similar levels as in placebo-nestlings. Self-degradable pellets proved to be an efficient tool to artificially elevate circulating baseline corticosterone especially in field studies, requiring only one intervention. The resulting peak-like elevation of circulating corticosterone, the concomitant elevation of CBG capacity, and the absence of an endogenous corticosterone response to an acute stressor have to be taken into account.

Feather corticosterone content in predatory birds in relation to body condition and hepatic metal concentration

“…In the present study, significant differences in feather CORT content between species were most evident between buzzard and sparrowhawk (both Accipitriformes species) whereas feather CORT concentrations did not differ significantly between barn owls, kestrels and tawny owls. This is consistent with reports that baseline and stress-induced levels of plasma CORT are similar in barn owls and kestrels (Almasi et al, 2012(Almasi et al, , 2013Meijer and Schwabl, 1989;Müller et al, 2009;Stier et al, 2009;Strasser and Heath, 2011).…”

Exploratory behaviour and stressor hyper-responsiveness facilitate range expansion of an introduced songbird

“…corticosterone receptors, corticosterone-binding globulins). Other studies have suggested that these factors may be controlled by baseline levels of corticosterone [42,43], which did not vary among populations at either time of year. Although this study was not designed to elucidate the hormonal mechanisms of exploratory behaviour, previous studies indicate that a relationship between corticosterone release and exploratory behaviour might exist; however, no such withinpopulation relationship was observed.…”

The dilemma of foraging herbivores: dealing with food and fear

“…Commercially available drugs can reduce systemic exposure and toxicity of ingested toxins (Seneca et al 2010). Likewise, the physiological stress response can be suppressed (Gagne et al 1985) or elevated (Muller et al 2009). …”