Abstract
In vertebrates, acute stressors-although short in duration-can influence physiology and behavior over a longer time course, which might have important ramifications under natural conditions. In laboratory rats, for example, acute stress has been shown to increase anxiogenic behaviors for days after a stressor. In this study, we quantified voluntary wheel-running behavior for 22 h following a restraint stress and glucocorticoid levels 24 h postrestraint. We utilized mice from four replicate lines that have been selectively bred for high voluntary wheel-running activity (HR mice) for 60 generations and their nonselected control (C) lines to examine potential interactions between exercise propensity and sensitivity to stress. Following 6 d of wheel access on a 12L∶12D photo cycle (0700-1900 hours, as during the routine selective breeding protocol), 80 mice were physically restrained for 40 min, beginning at 1400 hours, while another 80 were left undisturbed. Relative to unrestrained mice, wheel running increased for both HR and C mice during the first hour postrestraint (P < 0.0001) but did not differ 2 or 3 h postrestraint. Wheel running was also examined at four distinct phases of the photoperiod. Running in the period of 1600-1840 hours was unaffected by restraint stress and did not differ statistically between HR and C mice. During the period of peak wheel running (1920-0140 hours), restrained mice tended to run fewer revolutions (-11%; two-tailed P = 0.0733), while HR mice ran 473% more than C (P = 0.0008), with no restraint × line type interaction. Wheel running declined for all mice in the latter part of the scotophase (0140-0600 hours), restraint had no statistical effect on wheel running, but HR again ran more than C (+467%; P = 0.0122). Finally, during the start of the photophase (0720-1200 hours), restraint increased running by an average of 53% (P = 0.0443) in both line types, but HR and C mice did not differ statistically. Mice from HR lines had statistically higher plasma corticosterone concentrations than C mice, with no statistical effect of restraint and no interaction between line type and restraint. Overall, these results indicate that acute stress can affect locomotor activity (or activity patterns) for many hours, with the most prominent effect being an increase in activity during a period of typical inactivity at the start of the photophase, 15-20 h poststressor.
Highlights
By definition, short in duration; the physiological and behavioral effects produced by acute stress are often assumed to be transient
We predicted that the increase in activity would persist for up to 22 h, since corticosterone elevation is expected to be increased for at least 24 h following restraint, on the basis of studies of rats and Japanese quail (Fleshner et al 1995; Deak et al 1999; Armario et al 2008; Malisch et al 2010). This line of research is interesting because it may provide additional clarity for rodent exercise models of anxiety/ depression and because a finding of a change in circadian locomotor activity would aid in making predictions about the ecological or evolutionary significance of changes in behavior that result from acute stress in free-living populations
We predicted that high voluntary wheelrunning behavior (HR) mice would run more than C mice following restraint because HR mice typically are more active and have higher baseline corticosterone
Summary
By definition, short in duration; the physiological and behavioral effects produced by acute stress are often assumed to be transient. We predicted that the increase in activity would persist for up to 22 h (the length of the experiment), since corticosterone elevation is expected to be increased for at least 24 h following restraint, on the basis of studies of rats and Japanese quail (Fleshner et al 1995; Deak et al 1999; Armario et al 2008; Malisch et al 2010) This line of research is interesting because it may provide additional clarity for rodent exercise models of anxiety/ depression and because a finding of a change in circadian locomotor activity would aid in making predictions about the ecological or evolutionary significance of changes in behavior that result from acute stress in free-living populations
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