Induction of Fos protein in the rat trigeminal nucleus complex during an experimental tooth movement

The induction and temporal changes of Fos protein in the rat spinal trigeminal nucleus complex during experimental tooth movement were studied immunohistochemically. Separating elastics were unilaterally inserted between the upper molars. The animals were perfused at 0, 1, 2, 4, 8, 12 and 24 h thereafter, and the brains containing the mesencephalic trigeminal nucleus and the spinal trigeminal nucleus complex were then removed. Cells showing Fos immunoreactivity were observed in the superficial layers of the subnucleus caudalis on the ipsilateral side except at 0 and 24 h. The numbers of the immunoreactive cells peaked 2 and 4 h after the insertion. On the contralateral side, only a few immunoreactive cells were observed in the subnucleus caudalis of the 1-, 2- and 4-h groups. The subnucleus interporalis and the subnucleus oralis of the spinal trigeminal nucleus complex, the principal trigeminal nucleus and the mesencephalic trigeminal nucleus of the experimental animals and all the trigeminal nuclei of the control animals contained no immunopositive cells. Thus experimental tooth movement induced a Fos protein in the superficial layers of the subnucleus caudalis of the spinal trigeminal nucleus complex. The subnucleus caudalis may modulate pain induced by tooth movement.