Psychogenetically selected (Roman high- and low-avoidance) rats differ in 24-hour sleep organization

A comparison of sleep organization in Roman high-(RHA/Verh) and low-(RLA/Ve rh) avoidance rats, which differ in the way they respond to environmental s timuli and in several neuroendocrine and neurochemical parameters, was carr ied out. EEG-sleep recordings were obtained from adult males over 12:12 lig ht-dark periods to determine how these two psychogenetically selected rat l ines might also differ in their sleep-wake cycle. There was no significant difference in total sleep time between the two lines. However, the (hypoemo tional) RHA/Verh rats showed an overall increase (percentage of total sleep ) in paradoxical. sleep (PS) duration, with a concomitant decrease in slow- wave sleep (SWS). During the dark phase, RHA/Verh rats showed a shorter PS latency and a larger number of PS episodes. Hourly sleep scoring also revea led a more discontinuous pattern (total sleep and PS vs. SWS) during the da rk phase in RHA/Verh rats. In relation to recognized neurochemical and neur oendocrine differences between them, these rat lines may prove useful in in vestigations of the neurobiological mechanisms underlying sleep regulation.