Differential effects of trigeminal tractotomy on A delta- and C-fiber-mediated nociceptive responses

In this study we have tested in the rat, whether trigeminal tractotomy, whi ch deprives the spinal trigeminal nucleus caudalis (Sp5C) of its trigeminal inputs, affected differentially nociceptive responses mediated by C- vs. A delta-nociceptors from oral and perioral regions. Tractotomy had no effect on the threshold of the jaw opening reflex, induced by incisive pulp stimu lation (A delta-fiber-mediated), but blocked the formalin response (mainly C-fiber-mediated). These results suggest that nociceptive responses mediate d by trigeminal C-fibers completely depend on the integrity of the Sp5C, wh ile intraoral sensations triggered A delta-fibers (especially of dental ori gin) are primarily processed in the rostral part of the spinal trigeminal n ucleus. (C) 2000 Elsevier Science B.V. All rights reserved.