Circadian pattern of total and free corticosterone concentrations, corticosteroid-binding globulin, and physical activity in mice selectively bred for high voluntary wheel-running behavior

https://doi.org/10.1016/j.ygcen.2008.01.020Get rights and content

Abstract

In vertebrates, baseline glucocorticoid concentrations vary predictably on a diel basis, usually peaking shortly before the onset of activity. Presumably, circadian patterns in glucocorticoid secretion have evolved to match predictable rises in energetic need. In mice from lines selectively bred for high voluntary wheel-running, previous studies have reported that baseline plasma corticosterone concentrations at two different times during the photophase are elevated twofold above those of non-selected control lines. Here, we tested the hypothesis that the elevated daytime corticosterone levels could be explained by a shift in the circadian pattern of corticosterone levels. We measured baseline total plasma corticosterone levels, corticosteroid-binding globulin (CBG) capacity, and calculated free corticosterone levels (corticosterone not bound to corticosteroid-binding globulin and potentially biologically active) at six points during the 24-hour cycle in males on a 12:12 photoperiod. We also examined the daily pattern of both wheel-running and home-cage activity. Based on combined analysis of all six points, the circadian pattern of total corticosterone, corticosteroid-binding globulin, and free corticosterone levels did not significantly differ between high-runner and control mice (linetype  time interaction P = 0.56, 0.45, and 0.55, respectively); however, all varied with time (all P < 0.0001) and mice from the selected lines had significantly elevated total (P = 0.0125) and free (P = 0.0140) corticosterone, with no difference in CBG binding capacity (P = 0.77). All mice were active primarily during the dark phase, and the factorial increase in activity of selected relative to controls lines was 2.33 for total daily wheel revolutions and 2.76 for total daily home-cage activity. The onset of the active period for both measures of locomotor activity coincided with peak total and free corticosterone levels in both selected and control lines. These findings lend support to our hypothesis that elevated circulating corticosterone levels have evolved as an adaptation to support increased locomotor activity in the selected lines.

Introduction

Adrenal glucocorticoid hormones have highly integrated effects on both energy balance (Dallman et al., 1993, Pecoraro et al., 2005, Pecoraro et al., 2006, Dallman et al., 2007) and behavior (Breuner and Wingfield, 2000, Pecoraro et al., 2005, Pecoraro et al., 2006, Dallman et al., 2007). Under baseline conditions, plasma glucocorticoid (GC) levels vary predictably across a 24 h period (circadian variation) and, in some species, across the year in a seasonal pattern (for a review see Romero, 2002). Both circadian and seasonal patterns in GC secretion may have evolved to meet predictable rises in energy requirements (Romero, 2002, Pecoraro et al., 2006). For example, GC concentrations are highest around the time of arousal on a daily basis (morning for diurnal species and evening for nocturnal species), whereas seasonal peaks in baseline GC levels occur around the time of reproduction in several species of vertebrates, when energetic needs are often highest (Romero, 2002).

Acute elevations of circulating corticosterone (CORT) levels are superimposed on daily and seasonal fluctuations. In mammals (Lin et al., 1988, Lin et al., 1989, Coleman et al., 1998, Girard and Garland, 2002) and birds (Breuner et al., 1998, Lynn et al., 2003), CORT increases acutely in association with increases in locomotor activity. For example, in laboratory mice housed with access to wheels, plasma CORT concentration is significantly correlated with the number of wheel revolutions in the 20 min prior to blood sampling (Girard and Garland, 2002). Sparrows fed mealworms enriched with CORT display increased perch-hopping behavior (Breuner and Wingfield, 2000). Furthermore, ablation and replacement studies in rats have shown that CORT is necessary for rats to display schedule-induced wheel-running (Lin et al., 1988, Lin et al., 1989).

In a recent study, we reported that baseline plasma CORT levels of mice from lines that had been selectively bred for high levels of voluntary wheel-running are elevated twofold above those of their non-selected control lines (Malisch et al., 2007). Because of the known physiological effects of CORT that may support aerobically sustained exercise, such as increased lipolysis, proteolysis, and gluconeogenesis, with a simultaneous glycogen-sparing effect (Tharp, 1975, Coderre et al., 1992), we hypothesized that the increase in baseline CORT is an evolved (i.e., cross-generational) adaptation to support the high levels of wheel-running (nearly threefold higher than control mice). In addition, increased circulating CORT may promote wheel-running by increasing motivation to run. Running is a rewarding behavior (Belke and Garland, 2007, Brené et al., 2007) and elevation in plasma CORT increases the reward value of some behaviors. For example, increases in plasma CORT have been associated with increased self-administration of drugs, increased ingestions of saccharine, sucrose, and fats, and even increased self-administration of glucocorticoids (Piazza et al., 1993, Piazza and Le Moal, 1996, Piazza and Le Moal, 1997, Piazza and Le Moal, 1998, Bhatnagar et al., 2000, la Fleur et al., 2004, Pecoraro et al., 2004, Pecoraro et al., 2005).

Increased circulating CORT levels as a correlated response to selective breeding for high locomotor activity (Girard and Garland, 2002, Malisch et al., 2007) are an important finding from the perspective of evolutionary endocrinology (e.g., see Garland and Carter, 1994, Finch and Rose, 1995, Goymann et al., 2004, Ketterson et al., 2005, John-Alder and Cox, 2007, Zera et al., 2007), but downstream modulators could negate or amplify any effects of CORT on target tissues. For example, corticosteroid-binding globulin (CBG) circulates in the plasma and binds CORT with high affinity (Hammond, 1995). Although the exact function of CBG is unknown, one hypothesis is that CORT bound to CBG is biologically inactive (Mendel, 1989, Breuner and Orchinik, 2002). Like CORT, CBG levels are not static, and in mammals they can vary seasonally (Tinnikov, 1999), daily (Friaria et al., 1988, Hsu and Kuhn, 1988), and in response to stress (Tinnikov and Oskina, 1994, Fleshner et al., 1995, Spencer et al., 1996, Deak et al., 1999).

Here, we examine baseline total CORT, CBG levels, and calculated free CORT (the putatively biologically active fraction) at multiple points across the daily cycle. A finding that CBG is increased in HR mice would suggest that it might be buffering elevated CORT, and hence that elevated CORT may be a maladaptive byproduct of the selection regimen. In contrast, a decrease or no change in CBG levels would be consistent with the hypothesis that elevated CORT in HR mice may be an adaptation to promote wheel-running. We also compared the circadian pattern of total CORT, free CORT, and bound CORT with the circadian pattern of two measures of activity, home-cage and wheel-running.

Section snippets

Study animals

Adult (8- to 10-week-old) male Mus domesticus were obtained from an ongoing experiment in which four replicate lines of house mice are bred for high levels of voluntary running on days 5 + 6 of a 6-day exposure to wheels attached to standard housing cages (Swallow et al., 1998). Four replicate non-selected lines are maintained as controls (Swallow et al., 1998, Garland, 2003). Progenitors of these mice were from the outbred Hsd:ICR strain.

At weaning (21 days old), mice were toe-clipped for

Diel pattern of total CORT, CBG binding, and free CORT

For both high-runner and control lines, total CORT levels followed the expected diel pattern, with highest levels at 19:00 h, just prior to lights out (Fig. 1). Thus, time of day was a highly significant predictor of total CORT (Ptime < 0.0001). Linetype was also a significant predictor of total CORT (Plinetype = 0.0125), but the time  linetype interaction was not significant (P = 0.560), indicating that the daily pattern of CORT secretion does not statistically differ between HR and C males. In this

Discussion

Values measured for circulating CORT levels (see also Malisch, 2007) are similar to those from previous studies (Coleman et al., 1998, Malisch et al., 2007). Although the study of Malisch et al. (2007) on both sexes and that of Girard and Garland (2002) on females both indicated that HR mice have elevated baseline CORT relative to C mice, they examined only a few times. In addition, a recent study of HR males (at 10 and 18 months of age) indicated plasma CORT levels during the middle of the

Acknowledgments

We thank Leslie Karpinski and Jim Sinclair for their help maintaining the mouse colony, Glennis Julian and Haruka Wada for their generous help during CORT and CBG sample analysis, Kevin Middleton for writing the R script that was used to process wheel-running and home-cage activity data, Andrea Radtke and Shana Van Cleave for their assistance during data collection, and Wendy Saltzman and Henry B. John-Alder for comments on earlier versions of the manuscript. This work was supported by National

References (72)

  • S.E. Lynn et al.

    Short-term fasting affects locomotor activity, corticosterone, and corticosterone binding globulin in a migratory songbird

    Hormones and Behavior

    (2003)
  • N. Pecoraro et al.

    Glucocorticoids dose-dependently remodel energy stores and amplify incentive relativity effects

    Psychoneuroendocrinology

    (2005)
  • N. Pecoraro et al.

    From Malthus to motive: how the HPA axis engineers the phenotype, yoking needs to wants

    Progress in Neurobiology

    (2006)
  • P.V. Piazza et al.

    Glucocorticoids as a biological substrate of reward: physiological and pathological implications

    Brain Research Reviews

    (1997)
  • P.V. Piazza et al.

    The role of stress in drug self-administration

    Trends in Pharmacological Science

    (1998)
  • R.L. Spencer et al.

    Chronic social stress produces reductions in available splenic type II corticosteroid receptor binding and plasma corticosteroid binding globulin levels

    Psychoneuroendocrinology

    (1996)
  • S.E. Taymans et al.

    The hypothalamic-pituitary-adrenal axis of prairie voles (Microtus ochrogaster): evidence for target tissue glucocorticoid resistance

    General and Comparative Endocrinology

    (1997)
  • H. Wada et al.

    Development of stress reactivity in white-crowned sparrow nestlings: total corticosterone response increases with age, while free corticosterone response remains low

    General and Comparative Endocrinology

    (2007)
  • A. Angeli et al.

    Diurnal variation of prednisolone binding to serum corticosterone-binding globulin in man

    Clinical Pharmacology and Therapeutics

    (1978)
  • R.J. Adcock et al.

    Relationships between plasma cortisol, corticosteroid-binding globulin (CBG) and the free cortisol index (FCI) in pigs over a 24 h period

    Journal of Animal and Veterinary Advances

    (2006)
  • C.P. Barsano et al.

    Editorial: simple algebraic and graphic methods for the apportionment of hormone (and receptor) into bound and free hormone fractions in binding equilibria; or how to calculate bound and free hormone?

    Endocrinology

    (1989)
  • T.W. Belke et al.

    A brief opportunity to run does not function as a reinforcer for mice selected for high daily wheel-running rates

    Journal of the Experimental Analysis of Behavior

    (2007)
  • S. Bhatnagar et al.

    Corticosterone facilitates saccharin intake in adrenalectomized rats: does corticosterone increase salience?

    Journal of Neuroendocrinology

    (2000)
  • C.W. Breuner et al.

    Beyond carrier proteins plasma binding proteins as mediators of corticosteroid action in vertebrates

    Journal of Endocrinology

    (2002)
  • C.W. Breuner et al.

    Differential mechanisms for plasticity of the stress response across latitudinal gradients

    American Journal of Physiology: Regulatory, Integrative, and Comparative Physiology

    (2003)
  • J.L. Bunkers et al.

    Susceptibility of mice with chronically elevated plasma corticosterone to a parasitic nematode infection

    Integrative and Comparative Biology

    (2004)
  • S.E. Calvano et al.

    Circadian fluctuations in plasma corticosterone, corticosterone-binding activity and total protein in male rats: possible disruption by serial blood sampling

    Endocrine Research

    (1984)
  • L. Coderre et al.

    Effect of hypercorticism on regulation of skeletal muscle glycogen metabolism by epinephrine

    American Journal of Physiology

    (1992)
  • J. D’Agostino et al.

    Diurnal rhythm of total and free concentrations of serum corticosterone in the rat

    Acta Endocrinology

    (1982)
  • M.F. Dallman et al.

    Glucocorticoids and insulin both modulate caloric intake through actions on the brain

    Journal of Physiology

    (2007)
  • C.L. Dumke et al.

    Genetic selection of mice for high voluntary wheel-running: effect on skeletal muscle glucose uptake

    Journal of Applied Physiology

    (2001)
  • S.K. Droste et al.

    Effects of long-term voluntary exercise on the mouse hypothalamic-pituitary-adrenal axis

    Endocrinology

    (2003)
  • C.E. Finch et al.

    Hormones and the physiological architecture of life history evolution

    Quarterly Review Biology

    (1995)
  • M. Fleshner et al.

    A long term increase in basal levels of corticosterone and a decrease in corticosteroid-binding globulin after acute stressor exposure

    Endocrinology

    (1995)
  • R. Friaria et al.

    Influence of naturally occurring and synthetic glucocorticoids on corticosterone-binding globulin-steroid interaction in human peripheral plasma

    Annals of the New York Academy of Sciences

    (1988)
  • K. Fujieda et al.

    Regulation of the pituitary-adrenal axis and corticosterone-binding globulin-cortisol interaction in the guinea pig

    Endocrinology

    (1982)
  • Cited by (0)

    1

    Present address: Departamento de Fisiologia, Instituto de Biociencias, UNESP-Botucatu CEP: 18618-000, Brazil.

    View full text