S.K.J. and F.X.B. contributed equally to this work.
REM sleep: a sensitive index of fear conditioning in rats
Article first published online: 4 MAR 2005
European Journal of Neuroscience
Volume 21, Issue 4, pages 1077–1080, February 2005
How to Cite
Jha, S. K., Brennan, F. X., Pawlyk, A. C., Ross, R. J. and Morrison, A. R. (2005), REM sleep: a sensitive index of fear conditioning in rats. European Journal of Neuroscience, 21: 1077–1080. doi: 10.1111/j.1460-9568.2005.03920.x
- Issue published online: 7 MAR 2005
- Article first published online: 4 MAR 2005
- Received 23 July 2004, revised 29 September 2004, accepted 5 December 2004
- fear conditioning;
- post-traumatic stress disorder;
- REM sleep;
- Sprague–Dawley rats;
- unpaired control
To examine the influence of conditioned fear stimuli on sleep-wake states, we recorded sleep in Sprague–Dawley rats after exposure to tones previously paired with footshock. After habituation to a recording chamber and the recording procedure, a baseline sleep recording was obtained the next day. One day later, experimental animals were exposed to shock training designed to induce conditioned fear (FC), consisting of five tone-footshock pairings. The 5-s tones (conditioned stimuli; CS) co-terminated with 1-s footshocks (unconditioned stimuli; US). The next day sleep was recorded for 4 h in the recording chamber after presentation of five CSs alone. Sleep efficiency (total sleep time/recording period) and REM sleep (REM) and non-REM (NREM) measures were determined. While sleep efficiency was not significantly changed after CS presentation, the percentage of total sleep time spent in REM (REM percentage) was reduced in the FC animals. The reduction in REM percentage in the FC animals was due to a decrease in the number of REM bouts. In a separate experiment, we repeated the procedures, except the tones and shocks were presented in an explicitly unpaired (UP) fashion. The next day, presentation of the tones increased REM percentage in the UP group. Results are discussed in terms of the decreases in REM as a response to conditioned fear, and the relevance of these findings to the sleep changes seen in post-traumatic stress disorder (PTSD).