TY - JOUR
T1 - Sequential Changes in Cortical Excitation during Orthodontic Treatment
AU - Horinuki, E.
AU - Yamamoto, K.
AU - Shimizu, N.
AU - Koshikawa, N.
AU - Kobayashi, M.
N1 - Publisher Copyright:
© International & American Associations for Dental Research.
PY - 2016/7/1
Y1 - 2016/7/1
N2 - Cortical excitation responding to periodontal ligament (PDL) stimulation is observed in the rat primary somatosensory (S1), secondary somatosensory, and insular oral region of the cortex (S2/IOR), which are considered to process somatosensation, including nociception. Our previous studies have demonstrated that excitatory propagation induced by PDL stimulation is facilitated in S1 and S2/IOR 1 d after experimental tooth movement (ETM), and tetanic stimulation of IOR induces long-term potentiation of cortical excitatory propagation consistently. These findings raise the possibility that ETM induces neuroplastic changes, and as a result, facilitation of cortical excitation would be sustained for weeks. However, no information is available about the temporal profiles of the facilitated cortical responses. We estimated PDL stimulation-induced cortical excitatory propagation in S1 and S2/IOR of rats by optical imaging 1 to 7 d after ETM of the maxillary first molar. ETM models showed facilitated cortical excitatory propagation in comparison with controls and sham groups 1 d after ETM, but the facilitation gradually recovered to the control level 3 to 7 d after ETM. Sham groups that received wire fixation without orthodontic force tended to enhance cortical responses, although the differences between controls and sham groups were almost insignificant. We also examined the relationship between cortical responses and expression of inflammatory cytokines, interleukin (IL)-1β and tumor necrosis factor (TNF)-α, in PDL of the first molar. The peak amplitude of optical signals responding to PDL stimulation tended to be increased in parallel to the number of IL-1β and TNF-α immunopositive cells, suggesting that, at least in part, the enhancement of cortical responses is induced by PDL inflammation. These findings suggest that ETM-induced facilitation of cortical excitatory propagation responding to PDL stimulation 1 d after ETM recovers to the control level within a week. The time course of the facilitated cortical responses is comparable to that of pain and discomfort induced by clinical orthodontic treatments.
AB - Cortical excitation responding to periodontal ligament (PDL) stimulation is observed in the rat primary somatosensory (S1), secondary somatosensory, and insular oral region of the cortex (S2/IOR), which are considered to process somatosensation, including nociception. Our previous studies have demonstrated that excitatory propagation induced by PDL stimulation is facilitated in S1 and S2/IOR 1 d after experimental tooth movement (ETM), and tetanic stimulation of IOR induces long-term potentiation of cortical excitatory propagation consistently. These findings raise the possibility that ETM induces neuroplastic changes, and as a result, facilitation of cortical excitation would be sustained for weeks. However, no information is available about the temporal profiles of the facilitated cortical responses. We estimated PDL stimulation-induced cortical excitatory propagation in S1 and S2/IOR of rats by optical imaging 1 to 7 d after ETM of the maxillary first molar. ETM models showed facilitated cortical excitatory propagation in comparison with controls and sham groups 1 d after ETM, but the facilitation gradually recovered to the control level 3 to 7 d after ETM. Sham groups that received wire fixation without orthodontic force tended to enhance cortical responses, although the differences between controls and sham groups were almost insignificant. We also examined the relationship between cortical responses and expression of inflammatory cytokines, interleukin (IL)-1β and tumor necrosis factor (TNF)-α, in PDL of the first molar. The peak amplitude of optical signals responding to PDL stimulation tended to be increased in parallel to the number of IL-1β and TNF-α immunopositive cells, suggesting that, at least in part, the enhancement of cortical responses is induced by PDL inflammation. These findings suggest that ETM-induced facilitation of cortical excitatory propagation responding to PDL stimulation 1 d after ETM recovers to the control level within a week. The time course of the facilitated cortical responses is comparable to that of pain and discomfort induced by clinical orthodontic treatments.
KW - inflammation
KW - nervous system
KW - neuroscience
KW - orthodontic tooth movement
KW - pain
KW - periodontal ligament
UR - http://www.scopus.com/inward/record.url?scp=84975462503&partnerID=8YFLogxK
U2 - 10.1177/0022034516641276
DO - 10.1177/0022034516641276
M3 - Article
C2 - 27021255
AN - SCOPUS:84975462503
SN - 0022-0345
VL - 95
SP - 897
EP - 905
JO - Journal of Dental Research
JF - Journal of Dental Research
IS - 8
ER -