Role of the neural network of the brain stem in the inhibition of the rhythmical jaw movements

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It has been known that electrical stimulation to the focal area in the brain stem inhibits the rhythmical jaw movements (RJMs) evoked by repetitive stimulation to the cortical masticatry area (CMA). However, the physiological significance of that area has not been clarified. First, the neural network involved in the inhibitory effect on the RJMs was investigated in the rabbit using neuro-tracing methods. The inhibitory area was identified in the reticular formation adjacent to the periaqueductal gray matter. Injection of the anterograde tracer biocytine or retrograde tracer fluoro-gold was in this area conformed by the inhibitory effect. Labeled terminals by biocytine were found in the medial pontine reticular nucleus, and labeled cell by fluoro-gold was also found in the medial pontine reticular nucleus. This suggests that the reciprocal connection between the reticular formation adjacent to the periaqueductal gray matter and the medial pontine reticular nucleus may involved in the inhibitory effect on RJMs. Second, in order to know the feature of cortically induced RJMs, we investigated the cortico-striatal pathway from the CMA of the rabbit with electrophysiology and anatomical technique. Evoked potentials by stimulation to the CMA were recorded from the ventral part of the putamen. Injection of biocytine to the CMA resulted in that labeled terminals were located in the ventral part of the putamen. It is suggested that the ventral part of the putamen may involved in the control of masticatory movements.