Biology Reference
In-Depth Information
5.1. Neuroprotective effect of electrical stimulation on nervous
system
Many researchers have been studying the neuroprotective effects of electrical
stimulation of injured neurons for the past several decades. In the auditory sys-
tem, the survival of the spiral ganglion cells (SGCs) is the most common factor
that affects the performance of cochlear implants. Increased SGC survival
is expected to increase the sensitivity and improve thediscriminability. Chronic
electrical stimulation promoted the survival of SGSs which otherwise would
have degenerated from the administration of an ototoxic drug
in vivo
(
Hartshorn, Miller, & Altschuler, 1991; Lousteau, 1987
). The mechanisms
for the SGCprotection by chronic stimulationwere suggested to be an indirect
protection, secondary toprotectionof theorganof corti (
Lousteau, 1987
), met-
abolic activation of SGC through electrical stimulation, changes in cochlear
blood flow, changes in ion pump activity in the lateral wall of the cochlea,
and biochemical events in the neural membrane subsequent to stimulation
(
Hartshornet al., 1991
).
Leake,Hradek,Rebscher,&Snyder, (1991
)foundthat
SGC protection occurred in a region extending beyond the putative field of
neural activation, suggesting the potential for subthreshold protective effects.
Brief electrical stimulation enhances the regeneration of axotomized
motoneurons (
Al-Majed, Brushart, & Gordon, 2000; Nix & Hopf, 1983
)
and sensory neurons (
Brushart, Jari, Verge, Rohde, & Gordon, 2005
).
A brief electrical stimulation of a peripheral nerve proximal to the site of
the nerve transection and surgical repair promotes an earlier and marked
upregulation of BDNF and trkB in the axotomized motoneurons (
Al-
Majed, Neumann, Brushart, & Gordon, 2000
). This accelerated neuro-
trophic factor upregulation also occurs in sensory neurons (
Brushart et al.,
2002; Geremia, Gordon, Brushart, Al-Majed, & Verge, 2007
).
Examination of the regenerating axons in mice showed that electrical stim-
ulation promoted the sprouting of axons into the distal nerve stump, and the
effect of exogenous BDNF at the surgical site led to immediate nerve repair
by promoting sprouting (
Franz, Rutishauser, &Rafuse, 2008
).Thus,itislikely
that electrical stimulation and upregulation of neurotrophic factors in the neu-
rons play a key role in axon outgrowth from axotomized neurons. Consistent
with this notion, electrical stimulation for 1 h accelerated the upregulationof the
axon growth-associated protein GAP-43 (
Al-Majed, Tam, & Gordon, 2004
).
In the visual system, our laboratory has shown that electrical stimulation
to the cut end of the ON with monophasic pulses increased the number of
surviving RGCs in rats. The degree of survival depended on the parameters
of the electrical stimuli (
Morimoto, Miyoshi, Fujikado, Tano, & Fukuda,
2002; Okazaki, Morimoto, & Sawai, 2008
). These findings are consistent
