TARGET INFLUENCE ON AGING OF MYELINATED SENSORY NERVE-FIBERS

Large myelinated fibres in the rat inferior alveolar nerve (IAN) exhib it age-related aberrations partly similar to alterations in target-dep rived nerves. Shortly after entering the mandibular canal the rat IAN splits into a mental(MN) and an inferior dental (IDN) portion. This of fers a possibility to compare the occurrence of age-related aberration s in the MN and the IDN, which project to different target types. Henc e, we examined the relation between internodal length (L) and fibre di ameter (D) in teased fibre preparations of MNs and IDNs from adult rat s of different ages. The results show that the relation L/D is similar in MNs and IDNs of 6- to 24-month-old rats and that it is significant ly more irregular in IDNs than in MNs of 26- to 30-month-oldrats. This difference may be related to the fact that the IDN-innervated mandibu lar dentition is deteriorating in rats older than 2 years, whereas the muco-cutaneous target of the MN is not. We suggest that target deteri oration may be one major factor behind the increasing incidence of str uctural aberrations in large myelinated peripheral nerve fibres.