Electrical axon guidance Flashcards
Brief history electricity
egypt - nile catfish 2750 BC benjamin franklin - storm, leyden jar 1779 celestial bed luigi galvani frogs legs 1818 galvanic corpse electrotherapies
20th century - electric fields in xenopus embryos
glass electrodes measure differnces neural fold, plate and blastopore
EF associated with developing neural plate
animal electricity
Mateucci 1831 - required for muscle contraction by nerves
How is an EF generated in tissues?
skin is a battery - channels
tight junctions between cells
injury allows sodium to flow out from 60mv to 0mV
localised leak produces an EF
How can you experimentally disrupt EF?
block sodium channels
Endogenous field disrupted
disrupted form of embryo
where does electric current exit embryo?
posterior
what happens if EF shunted to lateral flank?
no tail or posterior spinal cord
Bioelectricity in regeneration - children’s fingertips
wound closed, dry dressing - poor outcome
wound open, moist dressing - back to normal
explain bioelectricity in regeneration
injury current, ions transported out making EF
has to be above joint
normal voltage neural tube cells develop naturally in
400mv-1000mv
EF application in vitro - explain set up
take cells - coverslip over
2 electrodes connect to power supply - EF
EF through agar salt bridge, across medium and cells
mechanism of neurites turning growing and branching to cathode
VGCC and stores - increase calcium cAMP Rho GTPases rho + end = collapse cdc/rac42 - end = assembly
no calcium in medium
cathode turning delayed
not significant until 2 hours
what time frame is calcium important in?
first 2 hours
cAMP inhibited
no turning - usually 54 degrees but prevents it
GEF
guanine nucleotide exhange factor
inactive - active
GAP
GTPase activating protein
active - inactive
cdc42 works on
filopodia
rac works on
lamellipodia
rho results in
growth cone collapse
Chemical stop signals
nogo/mag/omgp
cspg
activate rhoA
Where is RhoA elevated?
anodally
What can be used to inhibit Rho and what happens?
C3 transferase prevents turning
inhibition of rac1 and cdc42 on turning and growth cone
inhibits turning
rac inhibitor - sparse lamellipodia
cdc42 inhibitor - sparse filopodia
What are required for steering?
actin filaments
microtubules
rhodamine phallodin
bind to Factin
binds to microfilaments in filopodia and lamellopodia - red dye
vinblastine
prevent addition of new tubulin subunits to active microtubules
latruculin
interfere actin cytoskeleton in growth cone - absence of microfilament
taxol
drives all existing monomers into microtubules and freezes them
endocannabinoids
AEA resembles THC
binds CB1R
what does CB1R activate?
elevates RhoA
what does AEA/activation of CB1R result in? why?
prevent cathodal steering
lose gradient
Explain electrical therapy - how it done on guinea pig
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?
better battery implants?
oscillating field stimulator
possible future combined strategies for spinal cord repair
cAMP and rho GTPase no self medicating with cannabis drugs elevate cAMP EF scaffold to bridge the scar
