Nervous System Injury and Repair Flashcards
What’s about the longest distance that a peripheral axon can regrow?
About a foot.
What are two important things that Schwann cells might have that help axons regrow?
Adhesive molecules (so that the axons can follow their path) Trophic factors
What’s Ramon y Cajal’s neurotropic theory (or hypothesis)?
Regrowing axons are recruited by secreted factors to de-innervated Schwann cells in the distal nerve stump.
Why might the whole face move at once after the patient recovers from a CN VII (LMN) lesion?
Misrouting of regenerating axons -> signals cross.
Practical way to avoid misrouting axons?
Stitch together individual fasicles instead of just the whole nerve.
Why is CNS axon regeneration so limited? (1 instrinsic factor, 3 extrinsic factors)
Injured neurons just have low regenerative capacity.
Loss of trophic support from target.
Glial scar inhibits regrowth.
Inhibitory factors for axon regrowth (eg. stuff on central myelin)
Can addition of exogenous trophic factors help damaged CNS neurons survive longer?
Yes, but not long enough to be significant.
What do experiments with grafting PNS nerve onto lesioned CNS tracts show us?
CNS axons can in fact regrow in the permissive environment of the PNS graft. But they can’t regrow in the “hostile” environment of the CNS.
What’s one specific inhibitor of regrowth found in glial scars? Possible pharmacological intervention targeting it?
Chondroitin sulfate proteoglycan. Removing it with chondroitinase promotes axon regrowth.
Are regrowing CNS axons attracted to oligodendrocytes?
Nope. They’re repelled by them.
What are 3 inhibitory factors for CNS axon regrowth that activate a common pathway? What’s the pathway? Implication for pharmacological therapy?
Nomg, Omgp, MAG
All activate Rho.
Inhibiting Rho may promote axon regrowth. (but it hasn’t worked out so far)
What axons in the CNS do in fact regenerate regularly?
Axons of olfactory sensory nerves (OSNs) entering to synapse in the glomeruli of the olfactory bulb.
Where are the stem cells for interneurons in the olfactory bulb?
The subventricular zone.
Granule cells are generated postnatally in rodents. But are they in humans? How do we know?
Nope. Nuclear weapons testing radiation in the granular cells of adult humans is at the level corresponding to the year they were born. (recall that granule cells modulate output from mitral cells to the cortex)
What does the phenomenon of “chemo-brain” suggest about regeneration in the CNS?
We might have cells turning over in there after all…
