HRP 法による歯髄支配の三叉神経節及び中脳路核一次ニューロンの種差に関する研究

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Using the method of retrograde transport of horseradish perioxdase (HRP) the authors (1987, 1989) demonstrated the existence of the primary afferent neurons which innervate the tooth pulp in the feline mesencephalic trigeminal nucleus (MTN). In the present study with the same HRP method the possibility of dual innervation of the tooth pulp by the trigeminal ganglion (TG) and MTN was examined in a variety of mammalian species including the cat. HRP was applied to the pulp horn of the mandibular teeth excluding incisors in 4 rats, 4 rabbits, 4 cats, 3 dogs and one monkey ; all animals were subjected to postoperative administration of the anti-inflammatory steroid, prednisolone. The number and size of HRP-labeled neurons appeared in the TG and/or MTN as well as in the superior cervical ganglion (SCG) were measured. The number and size distributions were compared statistically among the TG, MTN, and SCG, and among the five species. The results obtained can be summarized as follows : 1) In the rat and rabbit labeled neurons were found in the TG, but none were found in the MTN. In the cat, dog and monkey, on the other hand, labeled cells were found both in the TG and MTN. All labeled cells appeared in the TG and MTN only on the side ipsilateral to the HRP application. 2) Within the TG the labeled cells localized in its posterolateral region corresponding to the mandibular division, which was common to the five species. 3) Within the MTN of the cat, dog and monkey the labeled cells, being either unipolar or pseudounipolar, were distributed in almost all rostrocaudal extent of the nucleus. The majority of the labeled neurons were concentrated to the caudal half of the MTN. 4) The soma diameter of all labeled SCG neurons having unmyelinated C fibers showed less than 36μm. Accordingly, the neurons in the TG and MTN were effectively separated into two categories, large cells and small cells, based on the soma diameter of 36μm. The large cells and small cells were considered to be the neurons having myelinated fibers and unmyelinated fibers, respectively. 5) In the cat labeled neurons in the MTN were significantly larger than those in the TG. 61.8% and 85.9% of labeled neurons in the TG and MTN were categorized into the large cells, respectively. In the monkey, on the contrary, labeled neurons in the TG were significantly larger than those in the MTN. 76.9% and 46.2% of labeled neurons were grouped into the large cells in the TG and MTN, respectively. 6) Assuming that the cell body diameter of the primary sensory neurons is in proportion to their axon diameter, it is reasonable to regard the great majority of tooth-pulp neurons in the feline MTN and monkey TG as Aβ-range neurons being engaged in the low threshold mechanoreception. 7) In conclusion a conspicuous species difference was found in the primary sensory neurons which innervate tooth pulps in the rat, rabbit, cat, dog and monkey. Dual innervation of the tooth pulp by the TG and MTN occurred in the cat, dog and monkey, but not in the rat and rabbit. This species difference in pulpal innervation might be brought about by a cumulative dominance over the teeth closely associated with feeding habit.
九州歯科学会の論文
1996-08-25

HRP 法による歯髄支配の三叉神経節及び中脳路核一次ニューロンの種差に関する研究

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