Plasma corticosterone was measured with a commercially available ELISA kit. Blood was collected from 5 groups of mice. (1) Normal sleep without motor running (4 mice); (2) Forward running and normal sleep (3 mice); (3) Forward running and physical restraint (2 mice); (4) Forward running, physical restraint and then NREM sleep disturbance for 7 h (4 mice); (5) Forward running, physical restraint and then REMD for 7 h (5 mice). The level of corticosterone induced by gentle handling is comparable among NREM-d mice, REMD mice and mice with physical restraint. Data are presented as mean ± s.e.m., n.s. = not significant, Wilcoxon–Mann–Whitney test.