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

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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.