Response properties of periodontal mechanosensitive neurons in the trigeminal ganglion of rabbit and neuronal activities during grinding-like jaw movement induced by cortical stimulation

Objective: To examine the response properties of incisor- and molar-sensitive periodontal mechanosensitive (PM) neurons in the trigeminal ganglion of rabbit and the activities of the molar-sensitive PM neurons during the grinding-like jaw movement. Design: Discharges of PM units were recorded from the trigeminal ganglion with a microelectrode. The grinding-like jaw movement was induced by repetitive electrical stimulation of the cortical masticatory area. Results: Upper-incisor (UI) and upper-molar (UM) units were recorded from the rostromedial area of the trigeminal ganglion, and lower-incisor (LI) and lower-molar (LM) units were distributed in the caudolateral area. Most PM units were responsive to only one tooth, slowly adapting ones and responded to tooth stimulation of a force of less than 0.05 N. The optimal stimulus direction for most UI units was labio-lingual, axial or linguo-labial, and that for most LI units was linguo-labial or axial. The optimal stimulus direction of anterior UM and LM units was oriented predominantly mesio-distal or axial. The maximum frequency of spike discharges for UM units for which the optimal stimulus direction was axial or bucco-lingual was in the middle period of the grinding phase. However, UM units for which the optimal stimulus direction was mesio-distal or linguo-buccal were fired mostly in the early period. Conclusions: Periodontal sensory information in the grinding phase of jaw movement is transmitted by PM neurons with various response properties encoding the magnitude and direction of a force at least, in a weaker range of force than a saturating response level.