Convergence patterns of afferent information from the temporomandibular joint and masseter muscle in the trigeminal subnucleus caudalis

Convergence patterns of afferent information from the temporomandibular joint (TMJ) and the masseter muscle (Mm) in the trigeminal subnucleus caudalis in response to natural stimulation were examined in anesthetized rats for a better understanding of masticatory pain phenomena. All neurons tested (135) could be placed in one of the following three classes according to their responsiveness to natural stimulation in the TMJ and/or the Mm: Class I neurons, excited by only innocuous stimuli; Class II neurons, excited by only noxious stimuli; Class III neurons, excited by both. Afferent inputs from the TMJ and the Mm converged on 108 (80%) of the 135 neurons. Of these convergent neurons, 79% received nociceptive information from the TMJ and/or the Mm. The results suggest that convergent caudalis neurons that receive nociceptive information from the TMJ and/or the Mm may be important to referred pain associated with dysfunction of the masticatory system.