Regeneration in the PNS and CNS

Question 1

what is spinal decompression?

Answer 1

After trauma, damage to the spinal cord causes swelling.
Surgical decompression of the cord reduces this
enlargement.
to relieve the pressure on the spinal cord and/or spinal nerves.
This can be accomplished by removing damaged structures (eg, herniated disc, bone fracture) or soft tissues pressing on the cord and nerves—thereby creating space around these neural elements.

Question 2

what difference was shown in the clinical outcome of early vs late spinal decompression?

Answer 2

early spinal decompresssion was more likely to give rise to a better ASIA scale rating - greater frequency to improve on ASIA scale
both worked similarly one the lower scale

Question 3

what difference was shown in the clinical outcome of early vs late spinal decompression?

Answer 3

early spinal decompresssion was more likely to give rise to a better ASIA scale rating also both worked similarly one the lower scale

Question 4

what did Ramon y Cajal say about the regeneration in the Central nervous system?

Answer 4

“Once development was ended, the founts of growth and regeneration of axons dried up irrevocably. In adult centres the nerve paths are fixed, ended, immutable. Everything may die, nothing may be regenerated. It is for science to change, if possible this harsh decree.” (Ramon y Cajal, 1913)

Question 5

give an example of an animal with the ability to regenerate their CNS

Answer 5

The eel-like lamprey can fully regenerate its spinal cord after transection.

Within 3 months, an injured lamprey is able to swim, burrow, and flip around, as normal.

Repair and regeneration occur after retransection!

11 weeks after injury you can have full function – even after completely cut (with no bridge)

Question 6

give three reasons why Wallerian degeneration is successful in the PNS and not the CNS

Answer 6

Wallerian degeneration in the CNS fails due to the presence of inhibitory molecules (Nogo, MAG, OGmp), intrinsic lack of regenerative ability of CNS axons and no macrophages to clear debris

In the PNS the axons have intrinsically high regenerative ability and a permissive environment: macrophages clear debris and there are no inhibitory molecules present

Question 7

breifly why does axon regeneration fail in the CNS?

Answer 7

Axon regeneration fails in the CNS because of the inhibitory environment, and because of the intrinsic lack of regenerative ability of CNS axons.

Question 8

what areas of the spine are most commonly injured?

Answer 8

Further, the two most easily injured portions of the spine are the lumbar and cervical spines

Question 9

what areas of the spine are most commonly injured?

Answer 9

Further, the two most easily injured portions of the spine are the lumbar and cervical spines

Question 10

which regenerates better and why, a crush or cut peripheral nerve injury?

Answer 10

Crush lesions regenerate better than cut lesions due to intact extracellular matrix (ECM). Acts as guidance channel for regrowth

Question 11

what is needed for regeneration to occur in the peripheral nervous system?

conditions for successful regrowth

Answer 11

In order for regeneration to occur, Schwann cells must be present and form bands of Büngner before axons growth can occur.
The lesion gap must also be vascularised and fibroblasts must form connective tissue

Question 12

regeneration rate vary but what is usually the rate in successful cases?

Answer 12

~1-1.5mm/day

Question 13

why can muscle become severely atrophied after PNS injury?

Answer 13

Human peripheral nerve repair rate is around 1mm/day - this means that it could take years to repair some structures
proximal structures are well innervated but distal structures are poorly innervated
muscle endplates lose their ability to become re-innervated after around a year
therefore muscles can become severely atrophied in the absence of innervation

if muscles arent stimulated in a long time then they stop functioning

Question 14

describe an early experiment where they tried to use to PNS environment within the CNS for repair

Answer 14

In 1981 David and Aguayo discovered CNS axons can regenerate through a PNS graft
IN a rat spinal cord a lesion was made up towards the brain stem and a peice of sciatic nerve was implanted as a bridge above and below the lesion to provide a source of schwann cells (creating an environment similar to the PNS)
THe result showed that the CNS had regenerative potential under these conditions however the axons grew into the graft but not beyond back into the CNS

‘The Paper that Restarted Modern Central Nervous System Axon Regeneration Research’ Fawcett 2018

Question 15

describe the experiment that showed showed Peripheral injury enhances central regeneration of primary sensory neurones

why was this interesting but not clinically relevant?

Answer 15

In 1984 Richardson and Issa isolated the peripheral nerve ans induces a crush injury in edition to inducing injury in the spinal cord of a rat
they found that this enhanced the regeneration in the psinal cord
in studies that followed it was discovered that the crush in jury in the peripheral nerve upregulated a series of genes that induced a higher regenerative capacity (eg GAP43 and CAP23)

this is not clinically relavant because the peripheral nerve injury came before the spinal cord injury however it was informative in terms of the protein involvement

Question 16

describe the experiment that showed showed Peripheral injury enhances central regeneration of primary sensory neurones

Answer 16

In 1984 Richardson and Issa isolated the peripheral nerve ans induces a crush injury in edition to inducing injury in the spinal cord of a rat
they found that this enhanced the regeneration in the psinal cord
in studies that followed it was discovered that the crush in jury in the peripheral nerve upregulated a series of genes that induced a higher regenerative capacity (eg CAP43 and CAP23)

this is not clinically relavant because the peripheral nerve injury came before the spinal cord injury however it was informative in terms of the protein involvement

Question 17

what proteins are upregulated in the PNS immediately after injury?

Answer 17

actin, tubulin, and GAP-43 are upregulated immediately after injury

Question 18

injection of what proteins (‘chemicals’) can mimic the effect that a peripheral nerve injury has on enhancing regeneration in the spinal cord?

Answer 18

injections of cAMP, GAP43, CAP23

Question 19

what 5 intrinsic mechanisms are there to allow repair in neurons?

criteria for success

Answer 19

1. Neuron cell survival
2. Axon elongation
3. Axon guidance to target
4. Appropriate target innervation and synapse formation
5. Activation of target in functionally meaningful way (functional repair).

Question 20

what is neuronal plasticity?

Answer 20

refers to the capacity of the nervous system to modify itself, functionally and structurally, in response to experience and injury
ie can intact nearby neurons take over the function of damaged neurons

Question 21

what is the difference in neuronal plasticity between children and adults?

Answer 21

in the developing nervous system there is a high potential for plasticity
in the adult, mature nervoud system there is a low plasticity and regenerative ability

Question 22

when a neuron is damage what are three options for repair?

Answer 22

regeneration
replacement
plasticity

Question 23

what is the critical period of the nervous system?

Answer 23

Time during which reduction of neuronal numbers, remodeling of synapses and strengthening of connections occurs. Time when system is most vulnerable to external influences/stimuli

*	This period is the most influential time during development since permanent connections are established.
   Brain is more ‘plastic’ during this time period

Question 24

describe the experiment that compared the the cirtical periord in the visual system

between children and adults

Answer 24

they covered one eye of a child under 5 and an adult and waited
after a period of time, the child had undergone plastic changes in their bisual cortex that allowed a larger visual feild in the eye that wasnt covered - ocular dominance plasticty
in the adult, no changes occured in the mapping of the visual cortex

Question 25

what is ocular dominance plasticity?

Answer 25

a type of cortical plasticity operating in visual cortex of mammals that are endowed with binocular vision based on the competition-driven disparity
(if one visual feild is obscured then the unobscured eye will take over some of the obscured eyes territory if during the critical period

eye patches

Question 26

what are perineuronal nets?

Answer 26

Perineuronal nets are formed at the end of the critical period
They are composed of extracellular matrix (including CSPGs) which covers the cell soma and proximal dendrites of certain classes of neurons
Perineuronal nets inhibit plasticity in the adult CNS; set the networks in place

stained with WFA (wisteria floribunda agglutinin)

partial PNN knockout mice display increased plasticity following adult CNS damage (Carulli et al., 2010; Rowlands et al., 2018)

Question 27

what are the four steps to growth cone formation?

in aplesia

Answer 27

1. axotomy and destruction of axonal membrane - entrance of calcium > calcium increase > membrane depolarisation > activation of voltage gated Ca channels and release from intracellular stores
2. Ca2+ activates calpains which digest the spectrin cortex of the axon. Actin and MTs become depolymerised, vacuole interanlisation occurs and membrane begine to collapse at cut end
3. cut membrane reseals following membrane collapse by forming a sealing patch. Ca2+ levels decrease to normal and actin and MTs repolymerise
4. actin filaments assemble to generate force at leading edge of lemellipodium. MTs polymerise and point their + ends towards the plasma membrane

spectrin isa cytoskeletal component in axonal tips
small tip at reseal to make work more efficient

Question 28

describe the experiment that highlighted the importance of calcium in regeneration

Answer 28

Aplysia (sea slug) neurons were cutureed in low calcium and normal calcium conditions
A lesion was created
In low calcium conditions they did not see regrowth as vigorous as in the normal calcium culture

Question 29

what happens in axon growth cone formation/regeneration when calcium is absent?

Answer 29

In the absence of calcium, regeneration fails and a static endbulb is formed.

Question 30

where does the material needed to make a new growth cone come from?
(4)

Answer 30

1. Recycling of axonal molecules (actin, tubulin)
2. Transport vesicles on their way to the axon terminals
3. Local translation of mRNAs
4. Taken in from the environment

material recycled, taken in from environemtn or made brand new

Axotomy leads to upregulation of new proteins in cell bodies, which are needed for axon growth. Growth cone regeneration may happen too fast for these molecules to arrive.

Question 31

what three proteins expressed on oligodendrocyte myelin inhibit axonal regeneration?

Answer 31

Nogo-A,
MAG (myelin-associated glycoprotein),
and
OMgp (oligodendrocyte myelin protein

Question 32

what is MAG?

Answer 32

localised to compact, mature myelin; stabilises neuronal networks; growth permissive to embryonic neurons; is released upon damage into lesion

expressed on oligodendrocytes myelin, they inhibit axon regeneration

Question 33

what is NogoA

Answer 33

acts through a receptor complex involving p75 and NgR, affecting axon growth via calcium and RhoA signalling.

expressed on oligodendrocytes myelin, they inhibit axon regeneration.

Question 34

what is NogoA

Answer 34

.

Question 35

what is OMgp?

Answer 35

oligodendrocyte myelin protein
GPI-anchored protein; also expressed by neurons; mediates cell-cell interactions at nodes of Ranvier

expressed on oligodendrocytes, where they inhibit axon regeneration.

Question 36

antibodies for what protein helped increase the functional recovery in rat spinal cord injury

Answer 36

Anti-Nogo A antibodies increase axon regeneration in rat spinal cord injury

Question 37

AntiNogoA antibodies are inwhat stage of clinical trials at the moment?

Answer 37

Currently in phase II clinical trials – SCI; Phase I – MS

Not just looking at spinal cord injury but also sclerosis and stroke

Question 38

describe the experiment that showed AntiNogoA antibodies increase axon regeneration in rat spinal cord injury

Answer 38

In 2005 a group created a T lesion in the spinal cord of rats and then intrathecally applied AntiNogoA antibodies (11C7 and 7B12)
THey found that there was more growth in the lesion centre and even at the boundaries than the control ( 1.5-2.5mm away there was still nice growth – even up to 5mm away still nice growth)

T lesion - the dorsal cord is injured and the central part of the ventral cord is injured
Knocks out the doral column fibres – the dorsal column holds sensory fibres for vibration, pain, touch, proprioception
In a rodent the dorsal column also holds the corticospinal tract – the point of the lesion is to knockout the sensory fibres as well as those main corticalspinal tract fibres but leave some tissue in the ventral spinal lcord intact

similar testing has been done in primates and the therapy is inclinical trials for different CNS conditions

Question 39

knockout mice have been tested as an alternative to antibodies against NogoA. have they been as successful or not?

Answer 39

Knockout mice don’t show as favourable repair as antibodies.
* NogoA knockouts have produced variable amounts of axon regeneration after injury.
* One knockout regenerates vigorously
* One regenerates a bit
* One doesn’t regenerate at all.

Question 40

what are the major markers/cell surface molecule/cytokines produced by microglia?

in normal CNS

Answer 40

CR3
MCSF
TGFbeta1

Question 41

what are the major markers/cell surface molecule/cytokines produced by atrocytes?

in normal CNS

Answer 41

GFAP
CAMs
NGF
FGF
CNTF
TGFbeta1

Question 42

what are the major markers/cell surface molecule/cytokines produced by oligodendrocyte precursors?

in normal CNS

Answer 42

PDGFalphaR

Question 43

what is the main funcion/behaviour of microglia?

in the normal CNS

Answer 43

immunosurveillance

Question 44

what is the main funcion/behaviour of astrocytes?

in normal CNS

Answer 44

neuronal support

Question 45

what is the main funcion/behaviour of astrocytes?

in normal CNS

Answer 45

neuronal support

Question 46

what is the main funcion/behaviour of oligodendrocyte precursors cells?

in normal CNS

Answer 46

unknown
continually cycling population

Question 47

what is the main funcion/behaviour of oligodendrocyte precursors cells?

in injured CNS

Answer 47

rapid proliferation
hypertrophy

Question 48

what is the main funcion/behaviour of astrocytes?

in injured CNS

Answer 48

scar fromation
hypertrophy

Question 49

what is the main funcion/behaviour of microglia?

in injured CNS

Answer 49

antigen recognition, proliferation, hypertrophy

Question 50

what CS-PGs are expressed by microglia?

in normal CNS

Answer 50

none known

Question 51

what CS-PGs are expressed by astrocytes?

in normal CNS

Answer 51

Brevican, versican, phosphacan

Question 52

what CS-PGs are expressed by oligodendrocyte precursor cells?

in normal CNS

Answer 52

NG2
versican

Question 53

upon injury to the CNS microglial increase what cell surface molecules/cytokines?

Answer 53

CR3
MCSF
TGFbeta1
plus TNFalpha, IL1beta, IL6, B7, MHC1, CAMs ,MCSF-R, integrins

Question 54

upon injury to the CNS astrocytes increase which cell surface markers/cytokines?

Answer 54

GFAP, CAMS, NGF, FGFs, CNTF, TGFbeta1
plus, TNFalpha, IL1, IL6 and tenascin

Question 55

which CSPGs are increased and by which cell after injury to CNS?

Answer 55

astrocytes cause increase in brevican, versican, and phosphacan
oligodendrocyte precursors cause increase in NG2 and versican

Question 56

what is chondrotinase ABC?

Answer 56

Chondroitinase ABC (cABC) is an enzyme that digests glycosaminoglycan side chains of CSPGs.

Question 57

how do CSPGs in the glial scar prevent axonal regrowth?

Answer 57

Structure of CSPGs – has protein core and sugar side chain (glycosaminoglycan side chain ie GAG) and this is what produces steric hinderance making it a non permissive substrate for things to grow across

Question 58

what is the only certified treatment option for human patients with spinal cord injury?

Answer 58

Rehabilitive training
(the standard)
can the patient be helped with whatever function is remaining

Question 59

give an example of a steroid treatment that has been used for spinal cord injury?

Answer 59

methylprednisolone
- it relieves inflammation (swelling, heat, redness, and pain),
- given to control the swelling
- has many side effects but 20-30 years ago experimental studies showed that it did have a beneficial effect after spinal cord injury so then it became clinically applicable, neuroprotection it supplies is arguable
* Clinicians can be sued if they don’t provide it – because it has been seen as the standard of care in the US (doesn’t mean it provides that much protection

Question 60

describe the use of hypothermia as a neuroprotective treatment for spinal cord injury

Question 61

describe the mechanism of hypothermia mediated-protection

Answer 61

The neuroprotective action of hypothermia has been ascribed to its effect on a number of pathomechanisms including,
- the slowing of metabolism,
- decreasing cellular stress and
- reducing the generation of free radicals,
- ameliorating inflammation and
- inhibiting excitotoxicity that can reduce apoptosis,
- preserving the blood spinal cord barrier,
- preventing vasogenic edema,
- inhibiting astrogliosis,
- decreasing axonal damage,
- promoting neurogenesis as well as
- increasing angiogenesis

Question 62

what did cajal observe about the central nervous system after injury (cat/dog)?

Answer 62

Enlarged or hypotrophic neurons (look at cell bodies), axons turning around of themselves avoiding the area of inhibition and it the lighter coloured structures, neurons that were dying away.

Question 63

what are the current treatments for spinal cord injury?

Answer 63

• Spinal Decompression
• Neuroprotection (steroid treatments, hypothermia – only in rare cases )
• Rehabilitation
• Assistive devices

Question 64

why do CNS neurosn have an intrinsic lack of regenerative ability?

Answer 64

CNS neurons do not upregulate growth-associated genes to the same extent as do PNS neurons. Consequently, their ability to regenerate is limited even in the absence of inhibitors

Question 65

why do CNS neurosn have an intrinsic lack of regenerative ability?

Answer 65

CNS neurons do not upregulate growth-associated genes to the same extent as do PNS neurons. Consequently, their ability to regenerate is limited even in the absence of inhibitors

In contrast to the PNS, the upregulation of peripheral RAGs (see Sect. 2.2) is relatively modest in the CNS after injury (Fernandes et al. 1999; Marklund et al. 2006). This paucity of RAG expression appears to be partially responsible for the limited ability of CNS neurons to regenerate. Increasing RAG expression in CNS neurons improves their regenerative ability. For example, Bomze et al. (2001) demonstrated that overexpressing GAP-43 and CAP-23 together promotes sensory axon regeneration after SCI

Question 66

how long do schwann cells remain permissive for in denervated peripheral nerves?

Answer 66

2-3 months

Question 67

give an example of why peripheral regeneration is not always successful

Answer 67

if there is a crush injury in the shoulder there is such a long distance for regenerative capcity to work and bring back innervation to the hands and fingers
at a pase of around 1mm a day human peripheral nerve rapir rate might not be fast enough to recover this functions - because schwann cells only remain permissive for 2-3 months in denervated peripheral nerve and a muscle endplate lose their ability to become reinnervated after around 1 year

This means that proximal structures are well innervated and distal sturctures left poorly innervated

Question 68

partial perineuronal net knockout mice display increase……. following adult CNS damage

how can this be recapitulated in humans

Answer 68

partial PeriNeuronalNet knockout mice display increased plasticity following adult CNS

cant do this in human, but enzymatic digestion by chondroitinase can erduce the load of perineuronal nets

Question 69

describe the experiment that showed the problem is associated with mammalian myelin and not myelin of all animals

Answer 69

experiments done in 1981
myelin taken from a goldfish and neurons plated on top, they grow nicely
3T3 cells were grown on different species myelin and a diff substrate
On CNS myelin derived from a rat, cell didn’t put out processes,
On PNS myelin derived from a rat, they did start to put out some processes,
On polylysine substrate, they grew quite well
Experiment repeated using primary neurons, Superior cervical ganglion neurons from mammalian system. Did some differential plating with polylysine or rat CNS.PNS myelin and with that of a fishWe can see that the Cells are avoiding the mammalian CNS
they used laminin another growth promoting substrate, and myelin from rat and fish and grew primary neruosn. Presence of CNS rat myelin you can see long fibres grow on the laminin tracks and the myelin is inbetween avoiding the CNS myelin
On the goldfish one, the fibres were growing everywhere because the myelin is not inhibitory

these studies led up to the discovery of the inhibitory myelin proteins

Question 69

describe the experiment that showed the problem is associated with mammalian myelin and not myelin of all animals

Answer 69

experiments done in 1981
myelin taken from a goldfish and neurons plated on top, they grow nicely
3T3 cells were grown on different species myelin and a diff substrate
On CNS myelin derived from a rat, cell didn’t put out processes,
On PNS myelin derived from a rat, they did start to put out some processes,
On polylysine substrate, they grew quite well
Experiment repeated using primary neurons, Superior cervical ganglion neurons from mammalian system. Did some differential plating with polylysine or rat CNS.PNS myelin and with that of a fishWe can see that the Cells are avoiding the mammalian CNS
they used laminin another growth promoting substrate, and myelin from rat and fish and grew primary neruosn. Presence of CNS rat myelin you can see long fibres grow on the laminin tracks and the myelin is inbetween avoiding the CNS myelin
On the goldfish one, the fibres were growing everywhere because the myelin is not inhibitory

these studies led up to the discovery of the inhibitory myelin proteins

Question 70

what are the effects of a triple knocout of NogoA, MAG, OMgp?

Answer 70

shows no regeneration after injury
suggesting that transgenic forms regulate these proteins differently

Question 71

how do you ‘cure’ the environmental problem of inhibitory factors?

Answer 71

If you were to digest the GAG side chains with Condroitinase enzyme then you would non longer have the problem of the CSPGs
If add antiNogoA aswell then you have Cured environmental problem of inhibitory factors

Question 72

describe the first chondroitase studies done by Bradbury

Answer 72

Partial lesion of rat spinal column – cut the dorsal columns, administered chonroitinase at lesion site and looked for axons
In the lesion and saline you can barely see any axons. With chondroitinase you can see fibres going around the lesion area quite nicely.
Time frame looking at this regrowth was quite quick.
Since the publications, her team and others have stopped calling it regeneration and have alluded to the fact that it might be an increase in plasticity that is occurring.
She was able to identify a few fibres that came from non injured axons suggesting that plasticity was at least partially responsible for the effect
Axonal crossings, axonal sprouting and probably partial growth of intact fibres as well as regenerative growth

Following rodent spinal cord injury and digestion of glycosaminoglycan side chains with cABC, no CSPG immunoreactivity detected and fibres regrew around lesion site better than untreated

Question 73

describe the experiments that tested specific and non specific rehabilitation in control and chondroitase conditions

do you just need to be active or do you need to do specific things to recover these functions?

Answer 73

All spinal cord injury patients receive rehabilitation so it would be more representative if we rehabilitated animals with various tasks
Skilled forepaw reaching (wishaw task) – rat trained to reach for sugar pellet through small window – testing corticospinal tract function. Before the animal was injured they were trained to do this task.
After injury they were tested on this task again along side some daily practice time to rehabilitate the task - Specific rehabilitation
Another cohort of animals were given clay wheels to run around climb on - Non specific rehabilitation

With chondrotinase and specific rehab there were far move pellets retrieved in the reaching task.
However with penicillinase (the control) and specific rehabilitation a fair number of pellets was retrieved aswell far and above the chondroitinase with non specific or no rehabilitation at all.
Showing that rehabilitation is a viable way of treating spinal cord injury patients but chondroitianse can at least help a little bit

Question 74

what type of rehabilitation is most successful?

Answer 74

When you undergo rehabilitation, specific rehab is best to recover function rather than just being active – but also that combining rehab with a growth promoting treatment can be far and above better than one or the other alone

When you undergo rehabilitation, specific rehab is best to recover function rather than just being active – but also that combining rehab with a growth promoting treatment can be far and above better than one or the other alone

Question 75

what were the results of a combined rehabilitation, AntiNogoA and chondroitase on repair?

what was the caveat?

Answer 75

The combined treatment led to the most axons recovered

a viable treatment to recover growth and functional behaviour

the timing of adminsteration – could not apply AntiNogoA and chondroirinase at the same time. Apply AntiNogoA first and delay chondroitinase (if not they had bad reaction)

Question 76

why can’t we just abolish the glial scar?

Answer 76

Glial scar has a protective effect for the rest of the nervous system, it avoids a complete spread and destruction of tissue.
It walls off the lesion keeping it in one area
Taking the glial scar away completely you would miss out on some of the inflammatory responses (anti and pro inflammatory) and no longer have control of the lesion site (it may just expand)

a worst outcome is seen for the animal if it is

Question 77

describe the important of the glial scar for repair

Answer 77

“Despite acting as a physical barrier to axonal regrowth, the glial scar modulates the inflammatory response after injury and that without the glial scar present, this inflammatory response can be an equivalent barrier to regrowth.” (Quraishe et al 2018 Neural Plast)
Presence of “transitional” astrocytes with potential neuroprotective and immune-regulatory roles…

Question 78

cell transplants may provide what for regeneration and repair of SCI

Answer 78

1. Bridge over/through scar
2. Provide a growth Permissive substrate
3. Cell replacement (new cells to take place of dead ones)
4. Growth factors
5. Remyelination

Question 79

give three common cell transplant types for SCI

Answer 79

1. Schwann cells – (eg seen in peripheral nerve grafts)
2. Olfactory ensheathing cells
3. Stem cells
   * Induced pluripotent (little ethical implications)
   * Embryonic
   * Multipotent progenitors

Question 80

why are OECs a potentially viable means of treating spinal cord injury?

Answer 80

because of the relationship that they have with one of the few CNS cell types (olfactory neurons) that regenerates.

also they are a very accessible source -
a trained clinician can do a biopsy and extract these cell from an adult - to get an autologous transplant (donate your own to be used)

Question 81

what are olfactory ensheathing cells (OECs)

Answer 81

a unique class of vertebrate glial cells that envelop bundles of olfactory axons, both peripherally in the olfactory nerve and within the olfactory nerve layer (ONL) of the olfactory bulb
OECs sit at the top of the nose in the olfactory epithelium and enwrapping bipolar olfactory neurons (very accessible)
It has features of various cell types: the trophic support feature of an astrocyte, schwann cell feature of trophic support

Question 82

what molecular/functional features give OECs such potential for treating SCI

Answer 82

• They provide trophic support (i.e. neurotrophins); they can phagocytose debris, and they allow cells and axons to integrate through glial scar-rich regions
• Functional recovery and/or CNS axon regeneration has been reported when OB-derived cells where transplanted

Question 83

what is a major advantage OECs have over schwann cells for SCI?

Answer 83

axons can grow through an OEC transplant robustly - showing a bridge like tropic support capacity
they cannot grow through schwann cells

Question 84

why was the feild of OECs tarnished?

Answer 84

OEC craze got into the wrong hands – an unethical trial

In places like china and Portugal you could just buy some OECs for your SCI and they’ll transplant them in for about $20000.
A team of neuroscientist found they werent even OECs that were being transplanted
Put a whole load of doubt over the entire field and ruined it

even though Some proper clinical trials done in other countries such as Australia to show there was positive and beneficial effect of OEC transplants in spinal cord subjects. the feild is tarnished

Question 85

what replace OECs as the new hot cell to transplant?

Answer 85

Schwann cells are now picking up momentum, at a preclinical stage, testing pigs, ready for clinical trails anytime soon.
They have the ability to regrow fibres quite rigorously.

Question 86

describe the experiment that showed the potential of stem cell transplant for SCI

Answer 86

About 10 years ago, Mark Kozinski in UCSD California took injured rat spinal cord T3 (full transection lesion no fibres left intact)
Human Neural stem cells (NSCs) transplanted into immune-deficient mouse after T3 transection injury. Assessed for regeneration and axon growth, 7-12 weeks post-injury
Put embryonic stem cells (now neural stem cells expressing GFP)
Transplanted directly into the lesion site and assessed for growth at 7 to 12 weeks.
In red see cell bodies and green axons. There was capacity of the axons to grow around the bulous of cells. Showing the bridge like structure formed by transplanted cells.
Followed up with functional testing, animal tested to see if limbs and joints work. The open field score increased a lot, better locomotion.
Retransected the spinal cord and the scores dropped dramatically showing their recovery wasn’t an anomaly but by the treatment they put in.
Electrophysiology experiments show a similar effect – almost normal function seen.

Question 87

how many clinical trials are there currently using stem cells for SCI patients?

Answer 87

There are at least 38 ‘clinical trials’ going on around the world using stem cells in SCI patients

Question 88

what are biomaterials and how can they be used for regeneration and repair in SCI?

Answer 88

A material derived from, or produced by, biological organisms like plants, animals, bacteria, fungi and other life forms
Biomaterials may be natural or synthetic and are used in medical applications to support, enhance, or replace damaged tissue or a biological function
eg channels micropatterns porous materials

in a combined treatment with antibodies, enzymes, cell transplants

Question 89

give four ways biomaterials can be used for regeneration and repair in SCI?

Answer 89

1. Hydrogels that mimic the ECM
2. Provide physical or topographical cues for axonal growth
3. Substrate for cell delivery and survival
4. Important part of combined therapies (growth factors, cells, etc.)

Question 90

give four ways biomaterials can be used for regeneration and repair in SCI?

Answer 90

1. Hydrogels that mimic the ECM
2. Provide physical or topographical cues for axonal growth
3. Substrate for cell delivery and survival
4. Important part of combined therapies (growth factors, cells, etc.)

Question 91

how could electrical stimulation help rehabilitation after SCI?

Answer 91

Epidural stimulation uses electrical stimulation with propriospinal input derived from muscles, bones, and skin that project to the lower spinal cord (to serve as a source of neural control)
The electrical stimulator sits on the dura of the spinal cord, the thick outer meningeal layer. Electrical stimulation is pulsed in to target to proprial spinals in the spinal cord
targeting central pattern generators

Question 92

what are propriospinal (interneurons) neurons?

Answer 92

• Contained entirely within the spinal cord.
• May have short segmental or multi-segment projections.
• May convey supraspinal descending commands and aid in the integration of these commands with sensory feedback from the body.
• Mediate and coordinate rhythmic motor output involving multiple joints and neurons across several spinal segments
• They provide a large proportion of the excitatory and inhibitory inputs that the motor neurons receive

Question 93

what are central pattern generators?

the molecular basis of epidural stimulation?

Answer 93

Walking, swimming, etc. all depend on cycles of muscle activity
* For most quadruped mammals, it is assumed that the neural control of locomotion is based on CPGs within the spinal cord. This network generates the rhythm and shapes the pattern of bursts of motor neurons.
* Specialized neural circuits located in the caudal spinal cord (the CPG) organize hindlimb locomotor activity, while those in the rostral spinal cord control forelimb movement
* The coordination of both circuits is mediated by propriospinal neurons with long axons, which couple the cervical and lumbar enlargements of the spinal cord.

some people dont believe they exist

Question 94

describe the experiment that supports epidural stimulation

Answer 94

In 2011 people that were able to support their weight with walkers through rehabilitation or spatial lesions, using epidural stimulation they were able to walk and move their limbs to a greater degree suggesting that the epidural stimulation was stimulating the CPGs.
It was not inducing regenerative growth until many years later when this was studied after years of epidural stimulation
There is a suggestion that it has.
Weight-supported locomotor training + epidural stimulation resulted in walking (with assistive devices).

Question 95

after the studies in 2011 on epidural stimulation, what did the 2018 follow up report about the outcome

Answer 95

A follow up paper in 2018 said that
“Standing and voluntary movement were not driven solely by electrical stimulation but occurred only with the intention to move and when the sensory information of weight bearing during standing was provided…”

they also said that those who were more athletic and ‘strong’ had a better result

maybe placebo?

Question 96

what are the critical issues in regeneration research?

Answer 96

1. Small numbers of fibres regenerate (2-10%) in order to get a functional effect (no one knows)
2. Distance of regeneration.
3. Relevance of regeneration - proof?
4. Specificity of connectivity. (not all connections could be positive)
5. Adaptive and maladaptive.

Question 97

what things need to be considered for regeneration research

opposing ideas

Answer 97

• Acute versus chronic
• Focal versus diffuse
• Regeneration versus repair (plasticity?)
• Rehabilitation & Motivation

Question 98

what is the normal role of chondroitin sulphate proteoglycans?

Answer 98

are known to be involved in important cell processes like cell adhesion and growth, receptor binding, or cell migration.

Question 99

what are the two distinct regions of a glial scar?

Answer 99

Typically, the glial scar from traumatic injury in the CNS contains two distinct regions:
(1) the lesion core, which primarily consists of NG2 glia, fibroblasts/pericytes, and macrophages and
(2) the penumbra, which contains mostly reactive astrocytes and activated microglia.