[Modulation of spinal monosynaptic reflexes during rhythmical jaw movements and its central neural mechanisms].
The present study was carried out to investigate whether there was any modulation of the spinal monosynaptic reflexes during mastication in the healthy humans and urethane-anesthetized rabbits and to elucidate the central neural mechanisms responsible for the modulation in the urethane-anesthetized rabbits. 1. Human soleus H-reflex was significantly facilitated during the rhythmical jaw movements and rhythmical gum chewing. 2. There was no significant difference in the magnitude of the facilitation between the jaw-opening and -closing phases. 3. In the rabbits, monosynaptic reflex (MSR) volleys recorded from the tibial nerve (TIB) innervating the crural extensors and the common peroneal nerve (CP) innervating the crural flexors tonically increased in amplitude during the masticatory movements induced by either intraoral stimulation or repetitive stimulation of the cortical masticatory area (CMA). 4. Antidromic field potentials in the anterior horn of the lumbar cord evoked by the stimulation of TIB and CP increased during the CMA-induced actual and fictive mastication. 5. There was no significant change in the amplitude of the directly evoked antidromic potential in the primary afferents by intraspinal stimulation during the CMA-induced mastication compared with the resting state. It was concluded that (1) the MSR of the crural muscles undergoes a tonic non-reciprocal facilitation during mastication, (2) the stomatognathic afferents induced during mastication are not essential for the facilitation, and (3) an increase in the excitability of motoneurons is mainly involved in the facilitation of the MSR during mastication.
Hagiya
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Department of Stomatognathic Dysfunction, Faculty of Dentistry, Tokyo Medical and Dental University.
D000328:Adult; D000818:Animals; D006801:Humans; D007568:Jaw / Q000502:physiology*; D008297:Male; D008409:Mastication / Q000502:physiology; D009046:Motor Neurons / Q000502:physiology; D011817:Rabbits; D012023:Reflex, Monosynaptic / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology*