Electrical axon guidance

Question 1

Brief history electricity

Answer 1

egypt - nile catfish 2750 BC
benjamin franklin - storm, leyden jar
1779 celestial bed
luigi galvani frogs legs
1818 galvanic corpse
electrotherapies

Question 2

20th century - electric fields in xenopus embryos

Answer 2

glass electrodes measure differnces neural fold, plate and blastopore
EF associated with developing neural plate

Question 3

animal electricity

Answer 3

Mateucci 1831 - required for muscle contraction by nerves

Question 4

How is an EF generated in tissues?

Answer 4

skin is a battery - channels
tight junctions between cells
injury allows sodium to flow out from 60mv to 0mV
localised leak produces an EF

Question 5

How can you experimentally disrupt EF?

Answer 5

block sodium channels

Question 6

Endogenous field disrupted

Answer 6

disrupted form of embryo

Question 7

where does electric current exit embryo?

Answer 7

posterior

Question 8

what happens if EF shunted to lateral flank?

Answer 8

no tail or posterior spinal cord

Question 9

Bioelectricity in regeneration - children’s fingertips

Answer 9

wound closed, dry dressing - poor outcome

wound open, moist dressing - back to normal

Question 10

explain bioelectricity in regeneration

Answer 10

injury current, ions transported out making EF

has to be above joint

Question 11

normal voltage neural tube cells develop naturally in

Answer 11

400mv-1000mv

Question 12

EF application in vitro - explain set up

Answer 12

take cells - coverslip over
2 electrodes connect to power supply - EF
EF through agar salt bridge, across medium and cells

Question 13

mechanism of neurites turning growing and branching to cathode

Answer 13

VGCC and stores - increase calcium 
cAMP
Rho GTPases 
rho + end = collapse 
cdc/rac42 - end = assembly

Question 14

no calcium in medium

Answer 14

cathode turning delayed

not significant until 2 hours

Question 15

what time frame is calcium important in?

Answer 15

first 2 hours

Question 16

cAMP inhibited

Answer 16

no turning - usually 54 degrees but prevents it

Question 17

GEF

Answer 17

guanine nucleotide exhange factor

inactive - active

Question 18

GAP

Answer 18

GTPase activating protein

active - inactive

Question 19

cdc42 works on

Answer 19

filopodia

Question 20

rac works on

Answer 20

lamellipodia

Question 21

rho results in

Answer 21

growth cone collapse

Question 22

Chemical stop signals

Answer 22

nogo/mag/omgp
cspg
activate rhoA

Question 23

Where is RhoA elevated?

Answer 23

anodally

Question 24

What can be used to inhibit Rho and what happens?

Answer 24

C3 transferase prevents turning

Question 25

inhibition of rac1 and cdc42 on turning and growth cone

Answer 25

inhibits turning
rac inhibitor - sparse lamellipodia
cdc42 inhibitor - sparse filopodia

Question 26

What are required for steering?

Answer 26

actin filaments

microtubules

Question 27

rhodamine phallodin

Answer 27

bind to Factin

binds to microfilaments in filopodia and lamellopodia - red dye

Question 28

vinblastine

Answer 28

prevent addition of new tubulin subunits to active microtubules

Question 29

latruculin

Answer 29

interfere actin cytoskeleton in growth cone - absence of microfilament

Question 30

taxol

Answer 30

drives all existing monomers into microtubules and freezes them

Question 31

endocannabinoids

Answer 31

AEA resembles THC

binds CB1R

Question 32

what does CB1R activate?

Answer 32

elevates RhoA

Question 33

what does AEA/activation of CB1R result in? why?

Answer 33

prevent cathodal steering

lose gradient

Question 34

Explain electrical therapy - how it done on guinea pig

Answer 34

dorsal hemisection - add in marker of initial injury
2 holes and glial scar in middle
electrodes on either side of injury
how far can axons go through injury?

Question 35

better battery implants?

Answer 35

oscillating field stimulator

Question 36

possible future combined strategies for spinal cord repair

Answer 36

cAMP and rho GTPase
no self medicating with cannabis
drugs elevate cAMP 
EF
scaffold to bridge the scar