Expression Of P2X₃ Receptors In The Rat Trigeminal Subnucleus Caudalis After Experimental Tooth Movement

Pain is one of the most troublesome and commonest problems encountered by orthodontists clinically. More and more researches have been focusing on this field. Considerable evidences have indicated that Adenosine Triphosphate (ATP) has played a crucial role in pain transmission as a possible neurotransmitter. P2X₃ receptor is one of ATP receptors, which was found to be attributed to pain transmission. Formerly studies in our team have suggested that P2X₃ receptor may be involved in orthodontic pain, which merely pay attention to periphery nerve system, however, spinal trigeminal subnucleus caudalis (Vc) has been found to be related to oral facial pain closely, which was considered as a part of central nervous system (CNS). Therefore, present research mainly investigated the P2X₃ receptor changes in Vc during experimental tooth movement in rat at early stage.43 male SD rats (200-250g) were selected for this research. There were 7 experimental groups (4h, 12h, 24h, d2, d3, d5, d7) and 2 control groups [Group A: intact rat ; Group B: rat received false experimental tooth movement].5 rats were involved in each experimental group and 4 rats were contained in each control group. 80g force was applied to upper left incisor and the first left molar using close Ni-Ti coil. Immunohistology was used to reveal the distribution of P2X₃ receptors in Vc.Results showed as follows:1. P2X₃ receptor staining was found in Vc, which was expressed in superficial layer of Vc dominantly. Predominant up regulation of P2X₃ receptor immunoactivity was found on the left side (ipsilateral) from 4h to 7 day. It started to significantly increase at 4h, peaked at 3 day, then decreased continuously, as compared with the Group B. This kind of rhythm change was similar to initial orthodontic pain responses investigated in clinical.2. The rhythm change of P2X₃ receptor staining was also found in Vc on the right side (Contralateral) during the 7 days long period when compared with Group B. It was interesting to find that P2X₃ receptor staining started to increase significantly at 12h, peaked on 5 day, then decreased constantly.3. Significant difference was found when compared the immunoactivity of P2X₃ receptor between the left and right side in Vc. The experimental side (left) showed significant increased immune positive neurons than that of the control side (right).4. As compared with former study of our team, which investigated the P2X₃ receptors changes in trigeminal ganglion (TG) after experimental tooth movement in rat at early stage, similar changes were found between the two individual studies.On the whole, P2X₃ receptor had a rhythm change in Vc of rat as a result of experimental tooth movement on ipsilateral side and contra lateral side, which was similar to the result in TG (periphery nerve system). Also, the rhythm change was almost correspondent to the pain response after the first arch wires were ligatured at the early stage clinically. Thus, P2X₃ receptor may play an important role in orthodontic pain. Furthermore, the change of P2X₃ receptor on the Contralateral side may reveal that nerve fibers of trigeminal ganglion may project to the contra lateral side in Vc limitedly. However, the delayed response of P2X₃ receptor after experimental tooth movement on contra lateral side should be further investigated. Meanwhile, more attention should be paid to the P2X₃ receptor in superdorasl nerve system.