EXPRESSION OF FOS IN THE RAT FOREBRAIN FOLLOWING EXPERIMENTAL TOOTH MOVEMENT

Orthodontic tooth movement is known to cause pain and discomfort to pa tients. Mechanically induced inflammatory responses in the periodontiu m are assumed to be related to the mechanism of pain sensation. An imm ediate-early gene, c-Jos, that is expressed within some neurons follow ing synaptic activation, is widely used as a marker for neuronal activ ity following noxious or innocuous stimulation. We have recently demon strated that experimental tooth movement produced Fos induction in the ipsilateral trigeminal subnucleus caudalis and in the bilateral later al parabrachial nucleus, which is known to be involved in the transmis sion of nociceptive information. As a further step, we investigated th e distribution of Fos-Like immunoreactive neurons in the upper brain r egions. Twenty-four hours after the commencement of the experimental t ooth movement, the Fos-like immunoreactive neurons appeared in the cen tral nucleus of the amygdala (Ce), paraventricular nucleus of the hypo thalamus (PVH), and paraventricular nucleus of the thalamus (PV) of th e experimental rats. The numbers of the labeled neurons were significa ntly increased by 639% (P < 0.001) and 644% (P < 0.001) in the ipsilat eral and contralateral sides of the Ce, respectively, by 292% (P < 0.0 01) and 307% (P < 0.001) in the ipsilateral and contralateral sides of the PVH, and by 264% (P < 0.0001) in the PV with respect to sham cont rol rats. These results suggest that nociceptive information caused by experimental tooth movement might be transmitted and modulated in sev eral regions of the forebrain.