[Induction of rhythmical activity in digastric muscles in an in vitro brainstem preparation from adult mice].

In this study, it was attempted to induce masticatory movements in an in vitro brainstem-spinal cord preparation isolated together with the orofacial structure from adult mice. 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 bath perfused with the ACSF. Repetitive electrical stimulation of the medullary pyramidal tract (MPT) induced rhythmic EMG activities in the digastric muscle (3.8-7.2 Hz). Bath and intra-arterial application of kynurenic acid (KYN) or D, L-2-amino-5-phosphonovaleric acid (APV) suppressed the rhythm. During application of KYN, the rhythmic EMG activity in the digastric muscle could not be induced, even though the intensity of stimulation was raised. On the other hand, during application of APV, stimulation at a higher intensity induced rhythmic EMG activities with a lower frequency and a smaller amplitude. The results showed that glutamate is involved in induction of the rhythmic EMG activities by stimulation of the MPT, and that excitatory effects via the N-methyl-D-aspaltic acid receptor is not indispensable for its induction.