A double exposure to social defeat induces sub-chronic effects on sleep and open field behaviour in rats

Social defeat, resulting from the fight for a territory is based on the resident–intruder paradigm. A male rat intruder is placed in the territory of an older, bigger and more aggressive male resident and is defeated. In the present study, a double exposure to social defeat increased sleep fragmentation due to an increased amount of waking and slow-wave-sleep-1 (SWS-1) episodes. Also, social defeats increased the amount of slow-wave-sleep-2 (SWS-2). In repeated exposures to an open field, socially defeated rats showed low central activity and persistent defecation indicating high emotionality. The strongest effects of social defeat on sleep and open field behaviour were seen sub-chronically after stress. Social defeat did not induce changes in rapid eye movement (REM) sleep (e.g. total amount, latency), sleep latency, sexual activity, body weight or adrenal weight. A negative correlation between habituation in open field central activity and total sleep fragmentation indicates a commonality of effects of social defeat on both behaviour and sleep.