Long-term effect of cued fear conditioning on REM sleep microarchitecture in rats.
OBJECTIVE
To study long-term effects of conditioned fear on REM sleep (REMS) parameters in albino rats.


METHODS
We have investigated disturbances in sleep architecture, including muscle twitch density as REMS phasic activity, and freezing behavior in wakefulness, upon reexposure to a conditioned stimulus (CS) on Day 1 and Day 14 postconditioning.


METHODS
Male Sprague-Dawley rats prepared for polysomnographic recordings.


METHODS
After baseline sleep recording, the animals in the experimental group received five pairings of a 5-sec tone, co-terminating with a 1-sec, 1 mAfootshock. The control rats received similar numbers of tones and shocks, but explicitly unpaired. On postconditioning days, after reexposure to tones alone, sleep and freezing behavior were recorded.


RESULTS
Conditioned fear significantly altered REMS microarchitecture (characterized as sequential-REMS [seq-REMS: < or =3 min episode separation] and single-REMS [sin-REMS: >3 min episode separation]) on Day 14. The total amount and number of seq-REMS episodes decreased, while the total amount and number of sin-REMS episodes increased. Further, the CS induced significant increases in freezing and REMS myoclonic twitch density in the experimental group. Reexposure to the CS produced no alterations in controls.


CONCLUSIONS
The results suggest that conditioned fear causes REMS alterations, including difficulty in initiating a REMS episode as indicated by the diminution in the number of seq-REMS episodes. Another finding, the increase in phasic activity, agrees with the inference from clinical investigations that retrieval of fearful memories can be associated with the long-term REMS disturbances characteristic of posttraumatic stress disorder.
Madan
Vibha
V
Laboratory for Study of the Brain in Sleep, Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia 19104-6045, USA.
Brennan
Francis X
FX
Mann
Graziella L
GL
Horbal
Apryle A
AA
Dunn
Gregory A
GA
Ross
Richard J
RJ
Morrison
Adrian R
AR
D000818:Animals; D001007:Anxiety / Q000523:psychology; D001921:Brain / Q000033:anatomy & histology* / Q000502:physiology; D003213:Conditioning, Psychological; D003463:Cues; D004195:Disease Models, Animal; D004576:Electromyography; D005239:Fear; D046352:Freezing Reaction, Cataleptic; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology; D017286:Polysomnography; D051381:Rats; D017207:Rats, Sprague-Dawley; D012895:Sleep, REM / Q000502:physiology*; D013313:Stress Disorders, Post-Traumatic / Q000523:psychology; D013997:Time Factors