Response properties of temporomandibular joint mechanosensitive neurons in the trigeminal sensory complex of the rabbit.

The neurophysiological properties of neurons sensitive to TMJ movement (TMJ neurons) in the trigeminal sensory complex (Vcomp) during passive movement of the isolated condyle were examined in 46 rabbits. Discharges of TMJ neurons from the rostral part of the Vcomp were recorded with a microelectrode when the isolated condyle was moved manually and with a computer-regulated mechanostimulator. A total of 443 neurons responding to mechanical stimulation of the face and oral cavity were recorded from the brainstem. Twenty-one TMJ neurons were detected rostrocaudally from the dorsal part of the trigeminal principal sensory nucleus (NVsnpr), subnucleus oralis of the trigeminal spinal nucleus, and reticular formation surrounding the trigeminal motor nucleus. Most of the TMJ neurons were located in the dorso-rostral part of the NVsnpr. Of the TMJ units recorded, 90 % were slowly adapting and 26 % had an accompanying resting discharge. The majority (86 %) of the TMJ units responded to the movement of the isolated condyle in the anterior and/or ventral directions, and half were sensitive to the condyle movement in a single direction. The discharge frequencies of TMJ units increased as the condyle displacement and constant velocity (5 mm/s) increased within a 5-mm anterior displacement of the isolated condyle. Based on these results, we conclude that sensory information is processed by TMJ neurons encoding at least joint position and displacement in the physiological range of mandibular displacement.

Response properties of trigeminal ganglion mechanosensitive neurons innervating the temporomandibular joint of the rabbit.

The primary mechanosensitive neurons innervating the temporomandibular joint (TMJ neurons) may play an important role in controlling mandibular movement and position. The purpose of the study was to investigate the neurophysiological properties of TMJ neurons during passive movement of the isolated condyle in 55 rabbits and the intact condyle in 29 rabbits. Discharges of TMJ neurons from the trigeminal ganglion were recorded with a microelectrode as the isolated condyle was moved manually and by a computer-regulated mechanostimulator and as the intact condyle was manually stimulated. A total of 237 TMJ neurons were recorded rostrocaudally from the mandibular nerve area lateral to the maxillary region in the dorsal half of the trigeminal ganglion. Of the recorded TMJ units, 97% were slowly adapting (SA) and 67% of the SA units had an accompanying ongoing discharge. The proportion of adaptation types and appearance of ongoing discharges for the isolated condyle did not differ significantly from those for the intact condyle. Most of the TMJ units (89%) responded multidirectionally to the rostral and ventral movements of the isolated condyle. The discharge frequencies of the TMJ units increased as the condylar displacement and velocity increased within a 5-mm anterior displacement of the isolated condyle. Displacement of the isolated condyle influenced the discharge frequency of the units to a greater extent than the velocity of the condyle movement. No responses of TMJ units were observed during the descending ramp. Based on these results, we conclude that sensory information is transmitted by TMJ neurons encoding joint position, displacement and velocity in a physiological range of mandibular displacement.

Physiological properties of molar-mechanosensitive periodontal neurons in the trigeminal ganglion of the rat.

Spike discharges from periodontal mechanosensitive neurones responding to the mechanical stimulation of molar teeth were recorded from the trigeminal ganglion of rats anaesthetized with pentobarbital sodium. Maxillary molar-sensitive units were close together in a narrow, lateral area of the maxillary division of the ganglion, whereas those of mandibular molar-sensitive units were scattered throughout the mandibular division. The majority of maxillary molar-sensitive units responded only to stimulation of the first molar. They were slowly adapting and responded most strongly to pressure applied to the lingual surface and buccal cusp of the tooth or to the buccal surface and lingual cusp. By contrast, approximately one-half of the mandibular molar-sensitive units were rapidly adapting, multitooth units that responded to tooth stimulation almost equally in all directions. The other half were slowly adapting and activated most effectively by pressure applied to the lingual surface and buccal cusp of the molar tooth. These slowly adapting units consisted of first molar-sensitive, single- and multitooth units. Differences in the response characteristics of the maxillary and mandibular molar-sensitive periodontal units may reflect differences in the sensory role of individual molars.