Differential responses of intracisternal injection of interleukin-1 ? 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)-1beta 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-1beta injected intracisternally did not change the digastric electromyogram (dEMG). However, 10 ng IL-1beta suppressed dEMG to 76+/-8 % of control values. In an inflammatory pain model, 10 ng IL-1beta injected intracisternally did not change formalin-induced noxious behavioral responses. However, 100 pg IL-1beta increased formalin-induced noxious behavioral responses. At higher dose of 10 ng IL-1beta it did not increase formalin-induced behavioral responses. Pretreatment with IL-1 receptor antagonist abolished hyperalgesic response of 100 pg IL-1beta. These results suggest that the intracisternal injection of IL-1beta 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-1beta receptor.