Electron Microscopic Studies on Wallerian Degeneration of Primary Afferent Neurons in Feline Mesencephalic Trigeminal Nucleus Which Innervate Tooth Pulps : I. Difference in Proportion of Degenerating Myelinated Axons in the Canine Tooth Pulp Between Cats Undergoing Trigeminal Ganglionectomy and Cats Receiving Trigeminal Neurotomy

Previously we demonstrated using retrograde transport of HRP primary afferent neurons innervating tooth pulps in the mesencephalic trigeminal nucleus (MTN) of the cat, dog and monkey. Presently an electron microscopic study was made to compare the proportion of degenerating myelinated axons in the inferior alveolar nerve (IAN) and the mandibular canine tooth pulp (MdTP) between 2 cats receiving complete cut of the left IAN at the mandibular foramen and 2 cats undergoing complete excision of cell bodies of the mandibular part of the left trigeminal ganglion (TG). The relationship of the incidence of degenerating myelinated axons to the survival period following the transection of IAN was examined with 10 cats. Two weeks after transection of the left IAN, IAN and MdTP peripheral to the cut site showed the maximum degeneration of 96.1-97.8% and 97.3-100%, respectively. Two weeks after destruction of the left mandibular TG cells, IAN and MdTP on the operated side showed the maximum degeneration of 82.6-83.5% and 86.8-90.4%, respectively. Thus the proportion of degenerating myelinated axons in IAN and MdTP was found to be lower in the cats with perfect destruction of the mandibular TG cells than in the cats with complete cut of the IAN by 12.6-15.2% and 6.9-13.2%, respectively. Taking into account of the previous histological report on average 345 myelinated axons enter each apex of the cat canine tooth, these results suggest that approximately 25-50 myelinated axons from the MTN cells enter the apex of the MdTP.