EFFECTS OF CHRONIC STRESS ON SLEEP IN RATS

The present study was conducted to determine the effects of chronic st ress on sleep using a rodent paradigm of around-the-crock signalled in termittent foot shock in which some rats can pull a chain to avoid/esc ape shock while another group of rats is yoked to the first group. We measured sleep using telemetry; four-channel EEG was collected 24 h/da y in rats during 2 prestress days; days 1, 2, 3, 7, and 14 during chro nic stress; and 3 poststress days. States of REM sleep, non-REM (NREM) sleep, and waking were scored for each 15-s period of the EEG recordi ngs. During the prestress period, rats slept (REM plus NREM) 55% of av ailable time during the light hours and 34% of the dark hours with the remainder represented by waking. On the first day of stress, total sl eep and, especially REM sleep, decreased markedly. By the second day o f stress, only REM sleep in the controllable stress group (but not the uncontrollable stress group) was still significantly decreased compar ed to prestress levels, and REM sleep returned to baseline levels by d ay 7 of stress. The recovery of sleep quantity was accomplished by inc reased sleep during the dark hours, resulting in a long-lasting disrup tion of normal circadian sleep patterning.