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. 2004 Mar 25;2(1):2.
doi: 10.1186/1740-3391-2-2.

Daily rhythm of nociception in rats

AJM Christina  1 , NJ Merlin, C Vijaya, S Jayaprakash, N Murugesh
Affiliations

Daily rhythm of nociception in rats

AJM Christina et al. J Circadian Rhythms. .

Abstract

BACKGROUND: Many behavioral and physiological variables exhibit daily rhythmicity. Few investigations of the daily rhythmicity in nociception have been conducted, and conflicting results have been obtained. The present study evaluated the daily rhythmicity in nociception in Wistar rats. METHODS: Nociception was investigated by Eddy's hot plate method, tail immersion method, and tail clip method. The latency between the noxious stimulus and the animal's response was recorded as reaction time. Separate groups of rats were tested in 4-hour intervals for 24 hours. RESULTS: There was clear daily variation in response latency. Reaction time was shortest a few hours before lights-on and longest at the light-dark transition. CONCLUSION: Nociception exhibits robust daily rhythmicity in rats. Sensitivity to pain is highest late in the dark phase of the light-dark cycle and lowest at the light-dark transition.

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Figures

Figure 1
Figure 1
Daily rhythmicity of nociception in rats The figure shows the daily variation in reaction time to nociceptive stimulation. Each data point corresponds to the mean (±SE) of 6 rats. The horizontal bar at the top indicates the timing of the light-dark cycle.
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