Figure 1.

Daily restraint is stressful to rats. (A) Plasma corticosterone was measured in anesthetized rats 1 hr after exposure to restraint stress. One (1 day, n = 8), four (4 day, n = 5), or seven daily (7 day, n = 7) exposures to restraint stress induced a significant increase in plasma corticosterone compared with home-cage control rats (Control, n = 10). After seven daily exposures to restraint stress, the adrenal gland habituated to the stressful stimulus. (B) Rats exposed daily to restraint stress (▴) gained significantly less body weight over time compared with home-cage controls (●), providing an independent verification that daily restraint is perceived by the rats as stressful.