Effects of rapid eye movement (REM) sleep deprivation on pain sensitivity in the rat

The relationship between pain and sleep stems to be reciprocal: if pain may interrupt or disturb sleep, poor sleep can also influence pain perception. However the influence of sleep disturbances on pain sensitivity remain poo rly investigated. The aim of this study was to assess the effect of REM sle ep deprivation on the reaction of rats subjected to different noxious stimu li. In each experiment 16 Wistar male rats were randomly assigned to two gr oups: controls (n = 8), and REM sleep deprived rats (n = 8). REM sleep depr ivation was elicited using the 'inverted flower pot technique. Four differe nt experiments were performed to assess the sensitivity to mechanical (voca lization threshold in paw pressure). thermal (tail withdrawal latency in ho t water immersion), electrical (envelope of 2nd peep in rail shock test) an d chemical (analgesic behavior in formalin test) noxious stimuli. All exper iments were performed over a 5-day period with baseline (day 1, day 2) in a dry environment and REM sleep deprivation (day 3, day 4 and day 5) in a we t environment. Under wet conditions, vocalization threshold in the paw pres sure test (-20%. P=0.005). and tail withdrawal latency in the hot water imm ersion test (-21%, P=0.006) were significantly lower, and the envelope of 2 nd peep in the tail electrical shock was significantly greater (+78%, P=0.0 09), in REM sleep deprived rats compared to controls. However, under wet co nditions the mean duration of nociceptive behaviors in the formalin test di d not differ between the two groups. In conclusion. REM sleep deprivation i nduces a significant increase in the behavioral responses to noxious mechan ical, thermal and electrical stimuli in rats. (C) 2001 Elsevier Science B.V . All rights reserved.