Differential responses of intracisternal injection of interleukin-1 β to acute and inflammatory orofacial pain model in freely moving rats

The present study was performed to investigate the modulatory role of central interleukin (IL)-1β in nociception with a nociceptive jaw opening reflex and an orofacial formalin test in freely moving rats. In an acute pain model, 10 pg, 100 pg and 1 ng IL-1β injected intracisternally did not change the digastric electromyogram (dEMG). However, 10 ng IL-1β suppressed dEMG to 76±8% of control values. In an inflammatory pain model, 10 pg IL-1β injected intracisternally did not change formalin-induced noxious behavioral responses. However, 100 pg IL-1β increased formalin-induced noxious behavioral responses. At higher dose of 10 ng IL-1β, it did not increase formalin-induced behavioral responses. Pretreatment with IL-1 receptor antagonist abolished hyperalgesic response of 100 pg IL-1β. These results suggest that the intracisternal injection of IL-1β modulate the transmission of nociceptive information in the orofacial area. The hypo/hyper-algesic responses of central cytokines seem to depend on the pain model or dose related manner and the hyperalgesic action seems to be mediated by IL-1 receptor.