Neural mechanisms of rhythm generation for mastication-analysis in an in vitro brain preparation from abult mammals

新生哺乳动物体外中枢神经系统制备的最新进展，为哺乳动物吸吮、呼吸和运动中枢节律产生的生理学研究提供了重要工具。本研究的目的是在体外分离的脑干-脊髓制备物中诱导咀嚼运动，并从成年哺乳动物的口面部结构中分离出来。将含有葡聚糖的人工脑脊液（ACSF）通过固定在降主动脉上的套管注入动脉内，并放置在灌注了ACSF的记录室中。用丝电极监测二腹肌肌电图。结果表明：(1)反复电刺激髓锥体束（MPT）可诱导二腹肌节律性肌电图活动；(2)肌酸浴和动脉灌注阻断mpt诱导的节律性肌电活动；(3) dl -2-氨基-5-膦戊酸溶液和动脉内应用可降低mpt诱导的节律性肌电活动的频率和幅度。这些结果表明，谷氨酸通过刺激MPT参与了MEG节律性活动的诱导，而NMDA受体的兴奋作用对其诱导并非不可或缺。这种体外制备将有助于研究进食运动中枢节律产生的神经机制。

The recent development of in vitro CNS preparations of newborn mammals has provided important tools for physiological investigation of central rhythm generation of sucking as well as respiration and locomotion. The aim of this research was to induce masticatory movements in an in vitro brainstem-spinal cord preparation isolated together with the orofacial structure form adult mammals. The preparation was perfused intra-arterially with an artificial cerebrospinal fluid (ACSF) containing dextran through a cannula fixed to the descending aorta, and was placed in a recording chamber perfused with the ACSF.EMG of the digastric muscle was monitored with wire electrodes. The following results were obtained : (1) repetitive electrical stimulation of the medullary pyramidal tract (MPT) induced rhythmic EMG activities in the digastric muscle ; (2) bath and intra-arterial application of kynurenic acid blocked the MPT-induced rhythmic EMG ectivities ; (3) bath and intra-arterial application of DL-2-amino-5-phosphonovaleric acid slowed the frequency and suppressed the amplitude of the MPT-induced rhythmic EMG activities. These result demonstrate that glutamate is involved in induction of the rhythmic MEG activities by stimulation of the MPT, and that excitatory effects via the NMDA receptor is no indispensable for its induction. This in vitro preparation will be useful for the investigation of neural mechanisms underlying the central rhythm generation of food ingestive movements.