THE EFFECTS OF MOTORTRIGEMINAL DENUCLEATION ON RAT MASTICATORY MUSCLES

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  • 平岩 徳一
    Department of Physiology, Faculty of Dentistry, Kyushu University

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  • effects of Motortrigeminal Denucleation

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The effects of electrical destruction of the trigeminal motor nucleus of rat masticatory muscles were investigated with the aid of histochemical, cytological and physiological experimental procedures. Atrophy of the muscle fibers occurred 5 to 7 days after denucleation. Changes in the histochemical properties were found after denucleation: oxidative enzyme and glycolytic enzyme decreased, and acid phosphatase increased. Myosin ATPase and acetylcholinesterase activity did not, however, change significantly. Ultrastructural study of the muscle after denucleation revealed the progressive loss of contractile materials and changes of sarcoplasmic substructures. Nerve terminals broke up into small fragments and were replaced by Schwann cells. When electrically stimulated, the muscles exhibited a slower rate of rise of contraction and time delay in reaching peak tension. The stimulus frequency to produce tetanic tension decreased. The cessation of spontaneous miniature end plate pontentials occurred abruptly about 30 hr after denucleation and depolarization of the membrane was observed. Extrajunctional acetylcholine supersensitivity appeared 2-3 days after denucleation and reached a maximum value 10 days after denucleation. Membrane resistance, effective resistance, time constant and length constant increased about five days after denucleation. The rate of rise of the action potential was reduced and the action potential became partially insensitive to tetrodotoxin.<BR>It is concluded that the degenerative effects of denucleation of the masticatory muscle after trigeminal motor nucleus destruction are the same as the effects of cutting the motor nerve. Therefore, in preparation of denervated muscle, the relatively simple procedure of denucleation is recommended in lieu of the more difficult cutting of the nerve fibers.

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