TY - JOUR
T1 - Circadian pattern of total and free corticosterone concentrations, corticosteroid-binding globulin, and physical activity in mice selectively bred for high voluntary wheel-running behavior
AU - Malisch, Jessica L.
AU - Breuner, Creagh W.
AU - Gomes, Fernando R.
AU - Chappell, Mark A.
AU - Garland, Theodore
N1 - Funding Information:
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 Science Foundation Grants IOB-0543429 (T.G.) and IBN-0202676 (C.B.). J.L.M. was partially supported by a Graduate Assistantship in Areas of National Need grant to the Department of Biology and a U.C. Office of the President Dissertation Year Fellowship Award.
PY - 2008/4/1
Y1 - 2008/4/1
N2 - 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.
AB - 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.
KW - Artificial selection
KW - Circadian rhythm
KW - Corticosteroid-binding globulin
KW - Corticosterone
KW - Experimental evolution
KW - Locomotor activity
UR - http://www.scopus.com/inward/record.url?scp=40849123723&partnerID=8YFLogxK
U2 - 10.1016/j.ygcen.2008.01.020
DO - 10.1016/j.ygcen.2008.01.020
M3 - Article
C2 - 18329645
AN - SCOPUS:40849123723
SN - 0016-6480
VL - 156
SP - 210
EP - 217
JO - General and Comparative Endocrinology
JF - General and Comparative Endocrinology
IS - 2
ER -