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

ObjectiveTo 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.DesignDischarges 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.ResultsUpper-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.ConclusionsPeriodontal 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.