DENTAL NOXIOUS INPUT REACHES THE SUBNUCLEUS CAUDALIS OF THE TRIGEMINAL COMPLEX IN THE RAT, AS SHOWN BY C-FOS EXPRESSION UPON THERMAL OR MECHANICAL STIMULATION

The first upper molar tooth was subject to noxious thermal or mechanical stimulation in anaesthetised rats. In some animals, the red-heated metal end of a dental filling instrument was placed upright, briefly, on the occlusal surface. In other rats, a fine explorer was introduced three times into the pulp through a drilling cavity. Brainstem and cervical cord of treated and control animals were immunoreacted for the Fos protein. Numerous Fos cells occurred in the dorsomedial part of the ipsilateral trigeminal subnucleus caudalis including the transition zone with the subnucleus interpolaris, and in lamina I at spinal segments C-1-C-2, but were lacking in more rostral trigeminal subdivisions. Findings support the exclusive processing of nociceptive dental input in the medullary and upper cervical dorsal horn.