Effects of social stimuli on sleep in mice: non-rapid-eye-movement (NREM) sleep is promoted by aggressive interaction but not by sexual interaction

Sleep is generally considered to be a process of recovery from prior wakefulness. In addition to being affected by the duration of the waking period, sleep architecture and sleep EEG also depend on the quality of wakefulness. In the present experiment, we examined how sleep is affected by different social stimuli (social conflict and sexual interaction). Male C57BL/6J mice were placed in the cage of an aggressive dominant male or an estrous female for 1 h in the middle of the light phase. The conflict with an aggressive male had a pronounced NREM sleep-promoting effect. EEG slow wave activity, a measure of NREM sleep intensity, was increased for about 6 h and NREM sleep time was significantly increased for 12 h. REM sleep was strongly suppressed during the remainder of the light phase after the conflict, followed by a rebound later in the recovery phase. The sexual interaction, in contrast, had only mild effects. Both NREM sleep and REM sleep were somewhat suppressed shortly after the interaction. In a separate group of mice, blood samples were taken to measure prolactin and corticosterone. The results suggest that the temporary suppression of REM sleep following the social stimuli may be partly due to elevated corticosterone. The different effects of the social stimuli on NREM sleep are not easily explained by differences in the hormone responses. In conclusion, although both social conflict and sexual interaction induce a strong physiological activation, only social conflict has a strong stimulatory effect on NREM sleep mechanisms.