The developing cervical spinal ventral commissure of the rat: A highly controlled axon-glial system
- 102 Downloads
The floor plate of the neural tube is of major importance in determining axonal behaviour, such that, having crossed, decussating axons do not cross back again. The ventral commissure (VC) of the spinal cord forms immediately ventral to the floor plate shortly after neural tube closure. It is the principal location in which decussating axons cross the midline. It is probably also of major importance in neural tube development, but has received relatively little attention. This study analyses the growth and development of the rat VC and also axon-glial relationships within it throughout the crucial prenatal period of extensive transmedian axon growth, when key biochemical interactions between the two tissues are taking place. The morphometric, stereological and immunohistochemical methods used show that the axonal and glial populations remain in a finely balanced equilibrium throughout a period of almost a hundred-fold growth of both elements. At all stages axons are highly segregated into small bundles of constant size by glial processes, to which they are closely apposed. Thus, glial-axon contact is remarkably precocious, uniquely intimate and persists throughout VC development. This suggests that the relationship between the two tissues is highly controlled through interactions between them. The VC is likely to be the physical basis of a second set of glial-axonal interactions, namely, those which are well known to influence axon crossing behaviour. In mediating these, the extensive axon-glial contact is an ideal arrangement for molecular transfer between them, and is probably the substrate for altering axon responsiveness and ensuring reliable transmedian decussation. The VC is therefore a segregating matrix temporally and spatially specialised for a range of key developmental axon-glial interactions.
Unable to display preview. Download preview PDF.
- ALTMAN, J. & BAYER, S. A. (1984) The Development of the Rat Spinal Cord. Berlin: Springer-Verlag.Google Scholar
- FRAHER, J. P. (1992) The CNS-PNS transitional zone of the rat: Morphometric studies at cranial and spinal levels. Progress in Neurobiology 3, 261–316.Google Scholar
- GALKO, M. J. & TESSIER-LAVIGNE, M. (2000) Biochemical characterisation of netrin-synergising activity. Journal of Biological Chemistry 75, 7832–7838.Google Scholar
- RATHJEN, F. G. & JESSELL, T. M. (1991) Glycoproteins that regulate growth and guidance of vertebrate axons: Domains and dynamics of the immunoglobulin/fibronectin type III subfamily. Seminars in Neuroscience 3, 297–307.Google Scholar
- WEIBEL, E. R. (1979) Stereological Methods, Vol. 1: Practical Methods for Biological Morphometry. London: Academic Press.Google Scholar
- WILLIAMS, M. A. (1977) Quantitative methods in biology. In Practical Methods in Electron Microscopy (edited by GLAUERT, A. M.) pp. 36–38. Amsterdam: North Holland Publishing Company.Google Scholar