Wounding alters blood chemistry parameters and skin mineralocorticoid receptors in house sparrows (Passer domesticus)

Abstract

Because skin is an important physical barrier against pathogens, the ability to quickly and effectively heal wounds directly impacts an animal's health. The hormone corticosterone (CORT) has many complex effects on immune function and can slow wound healing. It has been suggested that CORT's role during wound healing may be to act as a "brake" on inflammation and cell proliferation. This project aimed to clarify the role of CORT in the healing process by quantifying concentrations of its two intracellular receptors, glucocorticoid receptors (GR) and mineralocorticoid receptors (MR), in the skin of wounded (n = 9) or unwounded (n = 8) house sparrows (Passer domesticus) using radioligand binding assays. We also quantified GR and MR in liver, spleen and pectoralis muscle, as well as several blood chemistry parameters, hypothesizing that wounding would alter whole-body energy use. One day post-wounding, wounded birds had higher blood glucose and lower aspartate aminotransferase (a marker indicating muscle damage or catabolism) compared to controls, which may be related to animals' changing metabolic needs in response to lymphocyte and macrophage recruitment at the wound site. Birds had significantly decreased MR, but not GR, in the skin of wounded legs compared to the skin of unwounded legs. There was also a trend towards lower MR in wounded skin compared to unwounded birds. Receptors in the three other tissues did not differ between groups. This study suggests that decreasing the skin's sensitivity to CORT immediately after wounding may be a necessary part of the normal healing process in wild birds.

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

“…Circulating corticosterone could directly alter healing through its interactions with immune related cells and effects on inflammation (Rabin, 1999;Planey and Litswack, 2000;Sternberg, 2006). Alternatively, direct effects of corticosterone on healing may operate on a more localized level, for instance, through localized changes in skin corticosterone production (Taves et al, 2011;Vukelic et al, 2011) or receptors in the skin that bind to corticosterone (Tiganescu et al, 2014;Lattin et al, 2015) and independent of plasma corticosterone concentrations. It is important to note that blocking of corticosterone was no longer apparent at the time of wounding; therefore, any direct positive effects of reduced corticosterone on healing may have no longer been present.…”

“…Existing evidence (French et al, 2006;DuRant et al, 2015;Love et al, In prep) and the results of this study suggest that elevated corticosterone release during stressful events may inhibit an individual's ability to cope with subsequent stressors, particularly immune-related stressors (but see McCormick and Langkilde, 2014). Thus, individuals or populations of individuals with higher circulating corticosterone due to low resource availability (Romero and Wikelski, 2001;MacLarnon et al, 2014), altered developmental conditions (Kitasky et al, 2006;Meaney, 2001), predation (Boonstra, 1998;, social subordination (Virgin and Sapolsky, 1997), etc., are at greater risk of experiencing pathological effects of stress.…”

“…Using previously-established methods, corticosterone-elevated birds received dermal application on the neck between the feather tracts of 20 µg corticosterone dissolved in 20 µL DMSO twice daily throughout the duration of chronic stress (Schallin- Busch et al, 2008). To block secretion of corticosterone we injected 180 mg/kg body weight mitotane (ortho, para-DDD); dissolved in peanut oil into the pectoralis muscle of birds daily for 3 days (Breuner et al, 2000, 2015 prior to the start of chronic stress, and again on day five of the chronic stress protocol. Control and CORT treated birds received injections of peanut oil.…”

Background DNA damage is higher in summer than winter in both free‐living and captive birds

“…Furthermore, glucocorticoid receptor numbers in house sparrows vary seasonally in some tissues but not others (Lattin et al, 2013). For example, glucocorticoid receptor density changed seasonally in subcutaneous fat, kidney, liver, gastrocnemius, and pectoral muscle, but not in omental fat (Lattin et al, 2015). However, none of those tissues shared a seasonal peak in receptor density, suggesting that seasonal receptor changes occur in a tissue‐specific manner (Lattin et al, 2015).…”

“…For example, glucocorticoid receptor density changed seasonally in subcutaneous fat, kidney, liver, gastrocnemius, and pectoral muscle, but not in omental fat (Lattin et al, 2015). However, none of those tissues shared a seasonal peak in receptor density, suggesting that seasonal receptor changes occur in a tissue‐specific manner (Lattin et al, 2015). Because corticosterone titers are equivalent in the summer and winter in free‐living house sparrows (Romero et al, 2006), we predicted that DNA damage would be equivalent in both seasons but might vary by tissue type.…”