Alteration in REM sleep and sleep spindles’ characteristics by a model of immobilization stress in rat

Investigation of sleep spindles’ oscillations is increasingly considered as a major avenue of inquiry in analyzing the microarchitecture of sleep. Previous studies highlight a strong mutual interaction between sleep and stress. In the present study, we investigated the effects of multiple stresses, provoked by animal immobilization in the narrow Plexiglas boxes with additional stress by placing some stones on the floor. Male Wistar rats (n = 14) were subjected to 2 h of immobilization per day in a narrow, uneven and stony place for 3 consecutive days. The electroencephalogram (EEG) was recorded with stainless steel screw electrodes placed over the skull and the electromyogram (EMG) was recorded from dorsal neck muscles. The sleep stages were recorded during 2 h before and 2 h after stress exposure for 3 days. Apart from sleep stages’ variations, sleep spindles’ density as well as their time- and frequency-domain characteristics were investigated rigorously by a semi-automatic sleep scoring method developed in MATLAB. Results indicate that multiple stresses containing immobilization as well as physical stress attenuate rapid eye movement sleep (REM). However, the stress effect on spindles is more sophisticated in NREM stages. Although spindle density does not undergo a significant change, spindle amplitude and sigma power of EEG during spindles raised significantly. Besides, a decrease in the mean frequency of spindles depicts a dramatic multiplication in delta slow oscillations. An especially mixed immobility including psychological and physical stress which we applied could affect sleep stability through an alteration in the sleep spindles’ amplitude and frequency but not the density of spindles and also through a reduction in REM sleep.