|Budget Amount *help
¥3,100,000 (Direct Cost : ¥3,100,000)
Fiscal Year 1999 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1998 : ¥2,500,000 (Direct Cost : ¥2,500,000)
Periodontal mechanosensitive (PM) neurons contribute to intraoral sensation of the location, hardness and textures of foods. They also modifies jaw movement so that mastication is performed efficiently and smoothly. To investigate an effect of periodontal information on masticatory movement, the response properties of trigeminothalamic neurons in the brain stem, thalamic VPM nucleus and primary somatosensory cortex were studied, for a start, in the anesthetized rats. Trigeminothalamic neurons were recorded at levels from the caudal part of the trigeminal main sensory nucleus to the rostral part of the subnucleus oralis. PM neurons in the rostral and caudal areas were sensitive to the ipsilateral mandibular and maxillary incisor teeth, respectively. The were single-tooth units. When the tooth was stimulated in the several directions, the responses were varied. The optimal stimulus direction was oriented lingually or labially. Slowly adapting and rapidly adapting neurons were about half-and-half. Thalamic VPM nucleus neurons were distributed in a ventro-medial area at the rostral two-third. Neurons sensitive to the maxillary and mandibular incisor teeth arranged dorso-ventrally. Incidence of slowly adapting neurons decreases to 30%, all neurons had their receptive fields contralaterally. Somatosensory cortex neurons were represented in two areas. Neurons in a rostro-medial area were sensitive to the contralateral mandibular incisor tooth, and that in the caudro-leteral one were to the contralateral maxillary tooth. Almost all of them were rapidly adapting, single-tooth neurons. The response properties of PM neurons in the rat were different from those in the cat, as suggesting a difference in the masticatory jaw movement.