Responses of trigeminal subnucleus interpolaris neurons to afferent inputs from deep oral structures.

Responses of trigeminal subnucleus interpolaris neurons to natural and electrical stimulation of the temporomandibular joint (TMJ) and the masseter muscle (Mm) were studied in the anesthetized rat. Interpolaris neurons could be placed in one of three classes determined by their responses to noxious and innocuous stimuli: Class I, excited by only innocuous stimuli; Class II, excited by only noxious stimuli; Class III, excited by both. In each class, the conduction velocities of the primary afferents were roughly equivalent to those of small-diameter fibers. Approximately 70% of the interpolaris neurons tested received nociceptive inputs from the TMJ and/or the Mm. Most of these neurons had extensive convergence of afferent inputs, including the TMJ, the Mm, and/or the facial skin. The results suggest involvement of interpolaris neurons in the characteristics of deep pain, such as its spread and referral.