Analysis of neural mechanisms of transformation from sucking to mastication in in vitro brain preparations.

哺乳动物的摄食行为从吮吸到咀嚼，与牙齿萌出相吻合。在成年哺乳动物中，参与咀嚼节律产生的神经元位于脑干下部，并沿吻尾轴分布。本研究的目的是探讨体外吸吮节律产生的神经组织。用N-甲基-D-天冬氨酸(NMDA)沐浴，在新生大鼠分离的脑干-脊髓标本中，在舌下神经(XIIn)中诱导出节律性吸吮样活动(RSA)。由于自然吸吮由舌、面和颌肌的节律性活动组成，因此假设三叉神经(V)和面(VII)运动神经元在RSA过程中表现出节律性活动。在本研究中，我试图(1)在NMDA应用期间在这些神经中诱导节律性活动，(2)如果它们被诱导，则定位NMDA诱导节律性活动产生所必需的结构。实验是在分离自具有或不具有口面部结构的新生小鼠的脑干-脊髓标本上进行的。用抽吸电极记录每条神经的神经活动。用CCD摄像系统记录舌头和颌骨的运动。结果发现：(1)N-甲基-D-天冬氨酸可诱导V、VII和XII核的RSA；(2)也可引起颌骨和舌头的节律性吸吮运动；(3)在V、VII和桥髓交界处的脑干完全切断后，NMDA仍可在V、VII和XII核诱发RSA。这些结果表明，NMDA诱导的RSA活动分别位于脑干的不同水平，CPG(S)本身的重组是从吸吮到咀嚼转换所必需的。

Feeding behavior of mammals changes from sucking to mastication, coinciding with the teeth eruption. In adult mammals, it is thought that the neurons involved in the rhythm generation of mastication locate in the lower brainstem and distributed along rostro-caudal axis. The purpose of this study was to investigate the neural organization of the rhythm generation of sucking in in vitro preprarations. Rhythmical sucking-like activity (RSA) is known to be induced in the hypoglossal nerve (XIIn) in an isolated brainstem-spinal cord preparation from newborn rats with bath application of N-methyl-D-aspartate (NMDA). Since natural sucking consists of well-coordinated rhythmical activities of the tongue, face, and jaw muscles, it is assumed that the trigeminal (V) and facial (VII) motoneurons would show rhythmical activities during the RSA.In this study, I tried (1 ) to induce rhythmical activities in these nerves during NMDA application, and (2) if they are induced, to locate the structures essential for generation of the NMDA-induced rhythmical activities. Experiments were performed on brainstem-spinal cord preparations isolated from newborn mice with or without the orofacial structure. Neural activities were recorded from each nerve with suction electrodes. Movements of the tongue and jaw were recorded with a CCD camera system. It was found that (1) bath application of NMDA induced RSA in the V, VII, and XII ns, (2) it also induced rhythmical sucking-like movements of the jaw and tongue, and (3) after complete transections of the brainstem between the V and VII ns as well as the pontomedullary junction, NMDA still induced the RSA in the V, VII, and XII ns, These results demonstrate that separate rhythm generators for the NMDA-induced activities are located at the respective levels in the brainstem, and that the reorganization of the CPG(s) itself would be necessary for the conversion from sucking to mastication.