Interactions between brief restraint, novelty and footshock stress on subsequent sleep and EEG power in rats

Stress produces significant alterations in sleep that appear to vary with the type, intensity and duration of the stressor. Brief manual restraint may be stressful in rodents but is often required for experimental procedures. We examined the effects of brief manual restraint on sleep and its possible influence on sleep induced after footshock and after the opportunity to explore a neutral enclosure. Sleep was recorded during non-interrupted baseline and during 8-h light and 12-h dark periods after three sessions of 5-min manual restraint (M1-3), after 30 min in neutral enclosure alone (NE) or with previous manual restraint (mNE) and after 20 footshocks presented over the course of 30 min alone (FS) or with previous manual restraint (mFS). Compared to baseline, M1-3 increased total sleep and NREM during both light and dark periods and significantly increased dark period REM. Both NE and mNE increased dark period total sleep, NREM and REM; however, mNE also increased light period total sleep and NREM, but not REM. FS and mFS increased total sleep, NREM and REM during the dark period and total sleep and NREM during light period. FS also significantly decreased light period REM whereas mFS did not. M1, mNE and mFS significantly increased EEG delta power during NREM, but M2-3, NE and FS alone did not. The results revealed that manual restraint can increase sleep and EEG delta power and that increases in sleep may persist across repeated sessions whereas the magnitude of EEG delta power may vary across sessions. In addition, prior manual restraint may significantly alter the changes in sleep and EEG induced by footshock and by the opportunity to explore a neutral enclosure. The results suggest that mild stressors may interact in their effects on sleep.