It has been demonstrated that the interrelation between pain and sleep produces changes in sleep patterns and pain perception. Although some evidences suggest that sleep and pain may interact in a complex way, polysomnographic studies in animals with acute nociception are limited in number.
This study was carried out in order to evaluate the effect of intra-articular knee injection of uric acid on sleep-wake patterns.
Surgical electrode implantation was performed in seven anesthetized Wistar rats to carry out 10 h polysomnographic recordings. Acute nociception was induced by the intra-articular administration of 30% uric acid crystals into the knee joint of the right hind limb. Two recordings before and after intra-articular drug administration were obtained. Sleep-wake parameters were classified as (i) wakefulness (W), (ii) slow wave sleep (SWS), and (iii) rapid eye movement (REM) sleep. Frequency and duration from each parameter were evaluated under the two above-mentioned conditions.
Intra-articular administration of uric acid induced: (i) an increased duration of wakefulness (p=0.014), (ii) a decrement in the duration (p=0.001) and number of events (p=0.027) in REM sleep, and (iii) a decrement in the total sleep time (p=0.001). SWS did not present statistical differences between groups.
These data suggest that a nociceptive stimulus, induced by the intra-articular administration of uric acid, alters the sleep-wake equilibrium with REM sleep being particularly altered. However, further research concerning pain-sleep interaction is needed.