Abstract
Repetitive electrical stimulation of the mesencephalic reticular formation (MRF) in ketamineanesthetized guinea pigs induced a rhythmical jaw movement (RJM) resembling mastication. The RJM was monitored by the multiple unit activity in the anterior digastric motoneuron pool (DIGMUA) as well as by the EMG activity simultaneously recorded from the masseter and anterior digastric muscles on both sides.
The following results were obtained: 1. The RJM induced by the MRF stimulation was characterized by a large opening movement to the contralateral side than that which was induced by stimulation of the cortical masticatory area (CMA) . 2. The RJM induced from the medial MRF was accompanied by a well coordinated tongue movement, but that which was induced from the lateral MRF was accompanied by no tongue movements. 3. The cycle time of the RJM induced from the medial MRF was definitely longer than that induced from the CMA, but there was no difference between the RJM induced from the lateral MRF and that which was induced from the CMA. 4. The rhythmical activity of the masseter EMG appeared in phase bilaterally, as was that of the anterior digastric EMG. The EMG activities of both muscles appeared reciprocally during the RJM induced from the CMA, but they partially overlapped during the RJM induced from the lateral MRF. The medial MRF stimulation induced the digastric EMG activity alone. 5. After the animal was paralyzed, the MRF stimulation induced a rhythmical DIG-MUA in essentially the same pattern as before paralysis. 6. After the CMA-induced rhythmical masticatory activity (RMA) was abolished by a complete lesion of the pyramidal tract at the pontine level on both sides, the MRF stimulation could induce the same pattern of RMA as before the lesion. 7. After a precollicular postmammillary transection was performed, the MRF stimulation induced the same RJM as before the transection.
Microinjectionof L-glutamate into the lateral MRF induced the same RMA as that which was induced by electrical stimulation of the same region in the MRF.
It was concluded that stimulation of the MRF neurons can induce the RMA centrally with no intervention of either the upper brain including the CMA or the peripheral feedback afferents, and that the effect of MRF stimulation is mediated to the lower brain stem by a route other than the pyramidal tract. In addition, the MRF is assumed to be mainly activated from the upper brain including the feeding center in the hypothalamus as well as the limbic system.
