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Early structural changes in the axoplasmic cytoskeleton after axotomy studied by cryofixation
1Abteilung für Cytologie, Ruhr-Universität, Bochum, Federal Republic of Germany.
Abstract:
Alterations in the cytoskeleton were studied in the axoplasm of neurites at the tips of proximal stumps of transected chicken sciatic nerves. The studies were carried out using cryofixation with a nitrogen-cooled propane jet. The most immediate effect is the almost complete disassembly of axoplasmic microtubules. This consequently causes the axonal transport of membrane-bounded organelles to cease and results in an accumulation of mitochondria and vesicles of the smooth endoplasmic reticulum. The neurofilament network is partially disorganized. Neurofilaments become shorter and fragmented, and are linked by a large number of anastomosed cross-linkers. The neurofilaments become newly aligned to the axis of the axoplasm and are of normal length 48-72 h after the transsection. At this stage the newly formed neurofilament bundles are in close proximity to the anastomosed cisternae and profiles of the smooth endoplasmic reticulum. The axonal sprouts always show a normally organized cytoskeletal network. These studies support the idea that the rapid remodelling of the neurofilament network is apparently a local event, not dependent on the slow transport of cytoskeletal materials to the tip of the proximal stump. The repair of the degraded cytoskeleton may be in accordance with the function of the endoplasmic reticulum as Ca2+-sequestering membrane system, which may be involved in restoring the physiological conditions of the axoplasm.
Insights
Nerve injury causes rapid microtubule disassembly and neurofilament reorganization in chicken sciatic nerves. Cytoskeleton repair appears to be a local event, potentially involving the endoplasmic reticulum.
Area of Science:
- Neuroscience
- Cell Biology
- Biochemistry
Background:
- Nerve injury triggers significant cellular responses, including alterations to the neuronal cytoskeleton.
- Understanding the dynamic changes in the axonal cytoskeleton is crucial for nerve regeneration research.
Purpose of the Study:
- To investigate the immediate and subsequent alterations in the axoplasm cytoskeleton following nerve transection.
- To elucidate the mechanisms underlying neurofilament network remodeling and repair after injury.
Main Methods:
- Cryofixation using a nitrogen-cooled propane jet to preserve axoplasmic structures.
- Microscopic analysis of cytoskeletal components, including microtubules and neurofilaments, in transected chicken sciatic nerves.
Main Results:
- Immediate disassembly of axoplasmic microtubules, leading to cessation of axonal transport.
- Partial disorganization and fragmentation of neurofilaments, followed by realignment and restoration of normal length within 48-72 hours.
- Axonal sprouts exhibit a normally organized cytoskeletal network.
Conclusions:
- Rapid neurofilament network remodeling is a local event, independent of slow axonal transport.
- The endoplasmic reticulum may play a role in cytoskeleton repair by sequestering calcium ions and restoring axoplasmic conditions.