Interleukin-1 beta injected intracisternally inhibited NMDA-evoked behavioral response in the orofacial area of freely moving rats.

The brain-derived interleukin-1beta (IL-1beta) has been involved in the modulation of nociceptive processing. The direction of the effects, however, analgesia or hyperalgesia, is controversial. Here, we report the role of IL-1beta injected intracisternally in orofacial pain transmission. Experiments were carried out on 90 male SD rats and surgical procedures were performed under pentobarbital sodium. Intracisternal injection of 0.3 or 0.6 microg of N-methyl-d-aspartic acid (NMDA) produced intense scratching behavioral responses including vocalization, agitation and a desire to escape in a dose-related manner. The intracisternal injection of 1 or 10 ng IL-1beta significantly decreased the NMDA-evoked scratching behavioral responses. Pretreatment with an IL-1 receptor antagonist or naloxone, an opioid receptor antagonist, blocked the IL-1beta-induced antinociceptive response. These results suggest that cytokine injected intracisternally seems to produce antinociceptive effects in the NMDA-evoked pain model of the orofacial area and the antinociceptive effect seems to be mediated by an opioid pathway.