15 - Neural Regeneration Flashcards
Peripheral and central projections
1
2
3
1) Central to central
2) Central to peripheral
3) Peripheral to peripheral
Direction in which damaged peripheral neurons regenerate?
Proximal portion of the axon can regenerate distally.
Partial repair is more common than full repair.
Three main things that prevent regeneration in CNS
Structure, cell types, molecules and guidance/repellent cues
Normal neuron fibre
Central nucleus.
Dense Nissl substance (ribosomes, rER)
Neuron fibre two weeks post-injury
Peripheral nucleus
Loss of Nissl substance (chromolysis/chromatolysis)
Wallerian degeneration
Muscle fibre atrophy
Wallerian degeneration
Degeneration of axon and myelin sheath below site of injuty.
Debris phagocytosed by macrophages
Neuron fibre three weeks post injury (PNS)
Schwann cells proliferate, forming a compact cord.
Growing axons penetrate the Schwann cell cord
Muscle fibre atrophy
Rate at which axons regenerate (PNS)
0.5 - 3mm/day
Neuron fibre three months post injury
Successful regeneration.
Electrical activity restored
Muscle fibre regeneration.
Potential outcome of improper axon regeneration
Neuroma
Molecular, cellular responses that promote peripheral nerve regeneration
Macrophages rapidly remove myelin debris (dead Schwann cells)
Neuron expresses growth-related genes.
Axon growth cone follow neurotrophins, etc.
Regenerating Schwann cells promote axon regeneration
Is axon regrowth faster in cut or crushed axons?
Crushed.
Schwann cells and ECM are more continuous in a crush injury.
The more precise the alignment, the better the recovery, regeneration.
Main therapeutic approach to PNS injury
Microsurgery
Nerve crush versus cut injury.
Get dieback with both types of injury.
Better regrowth with crush.
Only variable regrowth with cut.
Example of a treatment for CNS injury
Can administer tissue plasminogen activator for a stroke to break up the clot.
Primary CNS injury
Physical damage, cell loss
Secondary CNS injury 1 2 3 4 5
Minutes to hours: Degenerative insults • Ischaemia • Ca2+ influx • Lipid peroxidation & free radical production • Glutamate excitotoxicity • BBB breakdown
Examples of treatments for CNS secondary injury
1
2
1 ) Methylprednisolone in some countries (not Oz)
2) Erythropoietin (Epo) in several clinical trials
Secondary CNS injury over hours to days
Hours to days/weeks:
• immune cell infiltration/microglial activation
• cytokines, chemokines, metalloproteases
Secondary CNS injury over days to weeks 1 2 3 4 5
- axonal degeneration
- demyelination
- apoptosis
- astrocytic gliosis & glial scar
- also syrinx (cavity) formation, meningeal fibroblast migration
Treatments for secondary CNS injuries over days to weeks
None, as of yet.
What stops axonal regeneration in the CNS?
1) Lack of trophic support
2) Axon regrowth is inhibited by the injury environment
Factors that attract axon growth
Brain derived neurotrophic factor
Why do some spinal injuries improve somewhat?
Axonal plasticity (not axonal regeneration). Axonal plasticity is where there is axonal sprouting from an uninjured axon.