Re-utilization of Schwann cells during ingrowth of ventral root afferents in perinatal kittens
| Autor: | Thomas Masterman, Mårten Risling, A Ingela M Nilsson Remahl |
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| Jazyk: | angličtina |
| Rok vydání: | 2008 |
| Předmět: |
Dorsum
Aging Histology Biology medicine Ventral Roots Animals Neurons Afferent Molecular Biology Ecology Evolution Behavior and Systematics Cell Nucleus Nerve Fibers Unmyelinated CATS Pia mater Cell Biology Anatomy Original Articles Spinal cord Axons Microscopy Electron medicine.anatomical_structure Nociception nervous system Animals Newborn Receptive field Cats Mesaxon Schwann Cells Spinal Nerve Roots Developmental Biology |
| Popis: | Ventral roots in all mammalian species, including humans, contain significant numbers of unmyelinated axons, many of them afferents transmitting nociceptive signals from receptive fields in skin, viscera, muscles and joints. Observations in cats indicate that these afferents do not enter the spinal cord via the ventral root, but rather turn distally and enter the dorsal root. Some unmyelinated axons are postganglionic autonomic efferents that innervate blood vessels of the root and the pia mater. In the feline L7 segment, a substantial proportion of unmyelinated axons are not detectable until late in perinatal development. The mechanisms inducing this late ingrowth, and the recruitment of Schwann cells (indispensable, at this stage, for axonal survival and sustenance), are unknown. We have counted axons and Schwann cells in both ends of the L7 ventral root in young kittens and made the following observations. (1) The total number of axons detectable in the root increased throughout the range of investigated ages. (2) The number of myelinated axons was similar in the root's proximal and distal ends. The increased number of unmyelinated axons with age is thus due to increased numbers of small unmyelinated axons. (3) The number of separated large probably promyelin axons was about the same in the proximal and distal ends of the root. (4) Schwann cells appeared to undergo redistribution, from myelinated to unmyelinated axons. (5) During redistribution of Schwann cells they first appear as aberrant Schwann cells and then become endoneurial X-cells temporarily free of axonal contact. We hypothesize that unmyelinated axons invade the ventral root from its distal end, that this ingrowth is particularly intense during the first postnatal month and that disengaged Schwann cells, eliminated from myelinated motoneuron axons, provide the ingrowing axons with structural and trophic support. |
| Databáze: | OpenAIRE |
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