| Popis: |
The roots of certain cranial and spinal nerves are particularly suitable for studying the growth, myelination and maturation of motoneuron fibres. Furthermore, their rootlets can be readily traced on serial sections in both PNS and CNS. Accordingly, they were used for a series of morphometic studies analysing the developmental changes involved in the segregation, growth, myelination and maturation of central and peripheral segments of large and small motoneuron fibres (1-9). These included analysis of age changes in the internodal morphology of the entire myelin sheath of both the Schwann cell and the oligodendrocyte. This permitted comparison of the myelinogenic responses to stimuli emerging the same axon bundles, both within and between the two classes of ensheathing cell (5,6,8,9). Extensive statistical analysis was performed on the myelin sheath thickness - axon calibre relationship for the developing internodes of large and small calibre motoneuron fibres (1,8,9). To test if this relationship was constant among all motoneuron fibre bundles, its setting was compared between nerves of similar developmental origin, peripheral distribution and function (10). The extent to which it varied between different levels along one and the same fibre bundle was also studied using dorsolateral vagal rootlets (14). A series of morphometric studies was performed on the developing CNS-PNS transitional zones of a number of rat cranial and spinal nerves to analyse the complex interaction, migration, and sometimes intermingling, of central and peripheral nervous tissues during this process (16-25). These contribute to understanding the wide variety of forms of the mature transitional zones (15,16,20-30), whether these lie at, peripheral to, or central to the plane of the CNS surface to which the nerve roots or rootlets which contain them are attached. CNS-PNS transitional node development was examined to assess the manner in which oligodendrocytes and Schwann cells modify their developmental behaviour in response to their unique relationship to one another in this location (20). |
