Features of nociception in female rats on the model of maxillofacial pain syndrome

Objective. To study nociceptive sensitivity in female rats on the model of maxillofacial pain syndrome. Material and methods. The study was conducted on 37 female Wistar rats. The animals were divided into groups: intact ones; animals receiving injection of physiological solution into temporomandibular joint (TMJ); rats with induced pain syndrome by injection of sodium monoiodoacetate into TMJ. Pain response threshold was studied considering latent period of tail withdrawal reaction under light-thermal stimulation (tail-flick method). Measurements were performed in diestrus phase of estrous cycle according to microscopy of vaginal swabs). Results. Intra-articular injection of sodium monoiodoacetate decreased latency period of tail withdrawal reaction in female rats during six estrous cycles after injection. The most pronounced decrease of this index in rats with pain syndrome occurs by the second estrous cycle after injection. There were no significant differences in nociceptive sensitivity of animals at subsequent stages of follow-up (from the third to the sixth diestrus). Conclusion. Injection of sodium monoiodoacetate into temporomandibular joint is accompanied by lower pain response threshold in female rats. These changes are more pronounced by the second estrous cycle and persist until the end of follow-up. These data indicate persistent maxillofacial pain syndrome under these conditions.