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J Physiol Vol 483, Issue Pt 1 pp 239-250
Copyright © 1995 by The Physiological Society
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Inhibitory effect of sympathetic stimulation on activities of masseter muscle spindles and the jaw jerk reflex in rats.

R Matsuo, A Ikehara, T Nokubi and T Morimoto

Department of Oral Physiology, Faculty of Dentistry, Osaka University, Japan.

1. To evaluate sympathetic effects on jaw muscles, the discharges of masseter muscle spindle afferents, jaw muscle electromyographic (EMG) activities and blood flow changes were compared in anaesthetized decerebrate rats before and during electrical stimulation of the cervical sympathetic trunk. 2. To eliminate the possibility of efferent control from the trigeminal motoneurones, muscle spindle activity was recorded from the cut peripheral end of the masseter nerve. The absence of a sympathetic component in the masseter nerve was confirmed by the horseradish peroxidase method. 3. Electrical stimulation of the sympathetic nerve at frequencies within the physiological range reduced muscle spindle afferent discharges evoked by passive jaw opening. 4. Sympathetic stimulation also reduced the EMG activity evoked by the jaw jerk reflex, which may reflect a sympathetic effect on spindle afferents. After cessation of stimulation, a transient increase in EMG activity was observed, which may be due to efferent supply from the trigeminal motoneurones. During rhythmical jaw movements, no sympathetic effect on EMG activity was detected. 5. The above sympathetic effect on muscle spindle afferents and EMG activity was independent of blood flow changes.




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Am. J. Physiol. Regul. Integr. Comp. Physiol.Home page
H. Ishii, T. Niioka, H. Watanabe, and H. Izumi
Inhibitory effects of excess sympathetic activity on parasympathetic vasodilation in the rat masseter muscle
Am J Physiol Regulatory Integrative Comp Physiol, August 1, 2007; 293(2): R729 - R736.
[Abstract] [Full Text] [PDF]




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