Relationship between the response properties of periodontal mechanosensitive neurons of the thalamus and cerebral cortex and masticatory movement in the rat

牙周机械敏感（PM）神经元有助于口腔内对食物的位置、硬度和质地的感觉。他们也修改下颚运动，使咀嚼进行有效和顺利。为了研究牙周信息对咀嚼运动的影响，我们首先研究了麻醉大鼠脑干三叉丘脑神经元、丘脑VPM核和初级体感皮层的反应特性。三叉丘脑神经元分布在三叉主感觉核的尾侧至口侧亚核的吻侧。喙侧和尾侧的PM神经元分别对同侧下颌骨和上颌切牙敏感。它们是单齿动物。当牙齿受到不同方向的刺激时，反应是不同的。最优的刺激方向是舌上或唇上。缓慢适应和快速适应的神经元大约各占一半。丘脑VPM核神经元分布在吻侧三分之二的腹内侧区。对上颌和下颌切牙敏感的神经元背侧排列。慢适应神经元的发生率下降到30%，所有神经元的感受野都是对侧的。体感觉皮层神经元分布在两个区域。前内侧区神经元对对侧下颚门牙敏感，后外侧区神经元对对侧上颌牙敏感。它们几乎都是快速适应的单齿神经元。大鼠的PM神经元的反应特性与猫的不同，这表明咀嚼颌运动的不同。

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.