Effects of social defeat on sleep and behavior: Importance of the confrontational behavior

Abstract

We studied the short- and long-term effects of a double social defeat (SD) on sleep architecture, EEG power and behavior. A few studies have shown that rats that fight back or oppose the resident during the social conflict seem less affected by the defeat than those that show quick submission and passivity. Our hypothesis was that rats showing rapid submission in the social defeat would exhibit the most pronounced alterations in sleep architecture and behavior. All rats were surgically implanted with telemetric transmitters for sleep recording. Rats in the SD group ( n = 10) were exposed to 1 h SD on two consecutive days, while control rats ( n = 10) were left undisturbed. Telemetric sleep recordings were performed before SD (day −1), day 1, day 14 and day 21 post SD. The open field emergence test was performed on day 9, day 16 and day 23. Acoustic startle responses were tested on day 24. Overall, SD rats as a group were not affected, neither short-term nor long- term, by the social conflict with regard to sleep architecture, EEG power or behavior. Effects of SD seemed to vary according to the behaviors that the intruder displayed during the confrontation with the resident. Compared to those SD rats showing quick submission (SDS, latency to defeat: 56 ± 20 s, n = 5), SD rats fighting the resident during one or both SD confrontations before defeat (SDF rats, latency to defeat: 158 ± 45 s, n = 5) showed more fragmented SWS, both in SWS1and SWS2 ( p < 0.05, both) at day 1. This effect became more robust after day 14 ( p < 0.05 and p < 0.01, respectively) and day 21 ( p < 0.01, both). Descriptively, SDS and SDF rats showed different sleep architecture prior to SD. SDF rats were less awake, had more SWS2, less SWS1, and more REM sleep. The pattern of differences in SWS1 and SWS2 was maintained throughout the experiment, suggesting that this might reflect a trait rather than an effect of social conflict. REM sleep descriptively increased in the SDS group compared to their own baseline prior to SD on day 1 and day 14. The change across days was not seen in SDF rats. In the emergence test, SDF rats showed longer latency to leave the start box at day 23 ( p < 0.05) and spent less time in the arena compared to those showing quick submission and passivity at day 16 and day 23 ( p < 0.05, both). The SDF rats failed to show response decrement in the startle test at the lowest sound level ( p < 0.01). Our results indicate that aggressivity in a social conflict induces chronic fragmented sleep. A rapid submission during a social confrontation induces less sleep change and this behavior might reflect greater flexibility and to be more adaptive than fighting back. University of Bergen and Norwegian Competence Center for Sleep Disorders.