Sleep alterations in an experimental orofacial pain model in rats

This study sought to assess sleep patterns in rats injected with Freund's adjuvant (FA) in the temporomandibular joint (TMJ) as a potential experimental orofacial pain model. Pain response to indomethacin was also assessed. Rats were implanted with electrodes to record electrocorticogram and eletromyogram signals. After a baseline (B) recording, they were injected with Freund's adjuvant (orofacial pain group, n=8) or saline (sham group, n=8) in the temporomandibular joint, and their sleep was monitored over two 12-h light periods. In the second phase of the study, after injecting Freund's adjuvant, indomethacin was administered (1 mg/kg p.o.) at 12- intervals, and sleep patterns were recorded for two additional light periods. The orofacial pain group showed a reduction in sleep efficiency during the two light periods compared with the baseline recording and with the sham group (p<0.001). Increases in sleep and paradoxical sleep (PS) latencies of approximately 200% and 420%, respectively, were observed, as well as an increase in the number of awakenings during both periods (p<0.001). Treatment with indomethacin increased sleep efficiency (p<0.001) and paradoxical sleep time (p<0.001). The number of awakenings (p<0.001) and sleep (p<0.001) and paradoxical sleep latencies (p<0.001) were reduced reestablishing the normal sleep pattern. The results showed the reliability and usefulness of the temporomandibular joint pain model to characterize sleep disturbances related to pain and its response to indomethacin.