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The sensory input of the Vth cranial nerve might play a great role in the feeding activity of the mammals, especially of the Japanese shrew-moles. After the transection of the pure sensory infraorbital nerve, a drastic structural disorder was observed in the rat masseter muscle. In order to give anatomical evidence as to whether the interference of the sensory input affects the peripheral effector, electron microscopic investigations were performed on the primary axons and neurons of the Japanese shrew-moles. The results obtained are as follows: The preganglionic part of the transected nerves showed drastic degenerative changes of the myelinated fibers, characterized by a prominent decrease in the large- and medium-sized myelinated axon fibers, a gradual numerical increase of the clustered or isolated unmyelinated axons, and the frequent appearance of macrophages. The ganglion cells exhibited displacement of the nucleus with infolding of the nuclear membrane, the appearance of a large amount of lipofuscin granules, and an increase of neurofilaments and reduced Nissl bodies. The transganglionic part of the sensory root exhibited mainly a predominant axonal destruction, accompanied by myelinated disintegration.

In summarizing the present experimental results of tooth extraction, it can be emphasized that the disturbance of the sensory input units from the teeth resulted in a definite degeneration of the primary neurons. On this ground, it is suggested that the lesion of the sensory input units in the masticatory computer system, according to the individual age affected, may become a large factor in impeding the masticatory activity and accelerating the aging of the masticatory function.