Sleep pattern in an experimental model of osteoarthritis

Osteoarthritis (OA) is a major healthcare burden of increasing prevalence. It has been demonstrated that the relationship between pain and sleep produces changes in sleep patterns and pain perception. However, electrophysiological studies in animal models of pain are limited. The current study examined the effect of chronic articular pain on sleep patterns in an experimental model of OA. Rats were implanted with electrodes for electrocorticography and electromyography. OA was induced in these rats by the intra-articular administration of monosodium iodoacetate into the left knee joint. Sleep recordings were monitored during light and dark periods lasting 12h each and were evaluated at baseline as well as on days 1, 10, 15, 20 and 28 after iodoacetate injection or assignment to sham or control groups. The pain threshold was also assessed by hot plate testing in other groups of rats at the same time points. The results demonstrated that OA significantly reduced the thermal pain threshold from day 10 until the end of experiment. OA rats exhibited reduced sleep efficiency, slow-wave sleep, paradoxical sleep and an increased number of microarousals during the light periods compared with the baseline as well as control and sham groups. These changes in sleep pattern occurred mostly between days 10 and 28. In the dark period, sleep disturbances were also characterized by decreased sleep efficiency, slow-wave sleep, and paradoxical sleep, although sleep was only initially fragmented. Thus, pain associated with the rat OA model causes alterations in sleep architecture by disrupting the sleep pattern.