Restraint increases prolactin and REM sleep in C57BL/6J mice but not in BALB/cJ mice

Sleep is generally considered to be a recovery from prior wakefulness. The architecture of sleep not only depends on the duration of wakefulness but a lso on its quality in terms of specific experiences. In the present experim ent, we studied the effects of restraint stress on sleep architecture and s leep electroencephalography (EEG) in different strains of mice (C57BL/6J an d BALB/cJ). One objective was to determine if the rapid eye movement (REM) sleep-promoting effects of restraint stress previously reported for rats wo uld also occur in mice. In addition, we examined whether the effects of res traint stress on sleep are different from effects of social defeat stress, which was found to have a non-REM (NREM) sleep-promoting effect. We further measured corticosterone and prolactin levels as possible mediators of rest raint stress-induced changes in sleep. Adult male C57BL/6J and BALB/cJ mice were subjected to 1 h of restraint stress in the middle of the light phase . To control for possible effects of sleep loss per se, the animals were al so kept awake for I h by gentle handling. Restraint stress resulted in a mi ld increase in NREM sleep compared with baseline, but, overall, this effect was not significantly different from sleep deprivation by gentle handling. In contrast, restraint stress caused a significant increase in REM sleep c ompared with handling in the C57BL/6J mice but not in BALB/cJ mice. Cortico sterone levels were significantly and similarly elevated after restraint in both strains, but prolactin was increased only in the C57BL/6J mice. In co nclusion, this study shows that the restraint stress-induced increase in RE M sleep in mice is strongly strain dependent. The concomitant increases in prolactin and REM sleep in the C57BL/6J mice, but not in BALB/cJ mice, sugg est prolactin may be involved in the mechanism underlying restraint stress- induced REM sleep. Furthermore, this study confirms that different stressor s differentially affect NREM and REM sleep. Whereas restraint stress promot es REM sleep in C57BL/6J mice, we previously found that in the same strain, social defeat stress promotes NREM sleep. As such, studying the consequenc es of specific stressful stimuli may be an important tool to unravel both t he mechanism and function of different sleep stages.