Behavioural responses and expression of P2X3 receptor in trigeminal ganglion after experimental tooth movement in rats

Objective To explore the role of P2X 3 receptor in pain induced by experimental tooth movement. Design Male Sprague-Dawley rats weighing 200–300 g were used. P2X 3 receptor distribution in the caudal one-third portion of the trigeminal ganglion (TG) was studied by IHC. Next, the changes of P2X 3 expression were detected by Western blotting 4 h, 1 d, 2 d, 3 d, 5 d, 7 d, 14 d after tooth movement. We then developed a behaviour pain model associated with directed mouth wiping. Finally, the effect of TNP-ATP on nociceptive-like behaviour was evaluated. Results Our results showed that P2X 3 receptors were expressed mainly in small- and medium-sized cells and experimental tooth movement led to an increase in staining of mandibular P2X 3 receptors. In addition, following experimental tooth movement, the expression of P2X 3 receptor in TG was statistically significantly up-regulated from days 1 to 5, with a peak on day 3. It was also found that the time spent on directed mouth wiping was dramatically increased by experimental tooth movement from days 1 to 7. The rhythm change of P2X 3 receptor expression in TG and the mouth wiping behaviour were in concert with the initial orthodontic pain responses. The directed mouth wiping behaviour was modulated in a force-dependent manner and could be attenuated by peripheral and systemic morphine. Furthermore, peripherally administered TNP-ATP could exert an analgesic effect on this pain model. Conclusion These results suggest that directed mouth wiping behaviour can be a reliable measurement of pain following experimental tooth movement in rats. The P2X 3 receptor is important in the development and maintenance of tooth movement pain and thus may be peripheral targets for analgesics in orthodontic pain control.