Expression of c-Fos-like immunoreactive neurons in the supratrigeminal region in the rat following noxious stimulation of the orofacial tissues.

This study was conducted to investigate immunohistochemically the expression of c-Fos in neurons around the trigeminal motor nucleus following application of mechanical force to a tooth, a mechanical pinch to the tongue, and paraformaldehyde injection into the periodontal ligament and masseter muscle. Following the application of all of these stimuli except pinching the tongue, a small number of c-Fos-like immunoreactive (Fos-LI) neurons were found in the ipsilateral supratrigeminal region. c-Fos expression was also detected in numerous neurons in the superficial laminae of the subnucleus caudalis in all experimental animals. Induction of c-Fos in the subnucleus caudalis and the supratrigeminal region indicates that Fos-LI neurons in the supratrigeminal region are involved in the processing of intraoral nociceptive signals.