DC lesion?

Klenow bakedbeans at spam.not
Sat Feb 14 02:43:19 EST 2004


In our journal club, we were discussing their chapter in the book Kindling 5
where they describe the Quenching effect on kindling.  We're pretty
skeptical about it so we looked to see what else they had done on it.  I'm
curious to know what people think of this.

Here's the article...

1: Exp Neurol.  1998 Nov;154(1):185-92.

Quenching revisited: low level direct current inhibits amygdala-kindled
seizures.

Weiss SR, Eidsath A, Li XL, Heynen T, Post RM.

Biological Psychiatry Branch, National Institute of Mental Health, Bethesda,
Maryland 20892, USA.

We have reported that low frequency stimulation (1 Hz for 15 min), applied
after
kindling stimulation of the amygdala, inhibited the development and
expression
of amygdala-kindled seizures, an effect we termed quenching. Subsequently,
we
discovered that this effect could only be achieved when certain stimulators
were
used that also emitted a low-level direct current (DC). The studies reported
here indicate that DC, applied once daily for 15 min at intensities of 5-15
microA, produced an intensity-related attenuation of kindling development
and an
increase in the afterdischarge threshold. This effect persisted in some
animals
for at least 1 month after discontinuation of the DC. In fully kindled
animals,
a robust increase in seizure threshold and persistent seizure inhibition
were
also observed using 10 microA of DC administered for 14 days. These results
clarify and extend our original findings of a quenching effect; however, the
mechanisms by which low level DC induces quenching require further
elucidation.


"NMF" <nm_fournier at ns.sympatico.ca> wrote in message
news:JEjXb.17152$sO4.1541938 at news20.bellglobal.com...
> Your right that really is a low current, however, depending on where they
> implanted the electrode you might be able produce an electrolytic lesion
> with extremely low current.  It might depend on whether they were using
> monophasic, biphasic fast ramps to deliever the stimulus current.
However,
> I think you said it was a low but constant current intensity, so square
wave
> currents (which can elicit lesions at very low current intensities) are
out
> of the picture.   For example, in the dentate with a low intensity current
> many cells have been shown to readily elicit prolonged burst firing.  The
> prolonged period of burst firing will allow for greater calcium entrance
> into the cell and the potential for deleterious accumulations of
> intracellular calcium, activation of internal stores, and consequential
> secondary messenger cascades.
>
> Generally the microcurrents used in many peripheral nerve stimulation
> experiments are in the 50-100 microAmp range.  Moreover, they elicit
potent
> analgesic responses.  (This is the premise of electroacupuncture
paradigms).
> So definitely potent cellular responses are likely at the low currents you
> suggest.  As an aside point, even picotesla intensity magnetic fields have
> been shown to elicit profound neuronal responses. (no evidence of cystic
> lesions though).  So definitely low intensity currents can elicit potent
> biological effects.
>
> Technically, it doesn't surprise me all that much that you can get a
> deleterious effect with such low intensity.  The cellular responses to
> electrical stimulation is often a U-shaped curve. With extremely minimal
> currents eliciting similar effects to that of high intensity currents.  In
> this case its probably the temporal component (the fact that its a long
> duration low intensity current) that is causing the effect similar to what
> would be encountered at higher intensity currents but have short time
range.
> That is also a common finding in sensory and motoric systems.  But its
also
> a routine finding in the literature involving learning and LTP vs. LTD
> (long-term potentation vs. long-term depression), where the specific level
> of current intensity determines which type of behavioral (physiological)
> response occurs.
>
> I wouldn't mind if you provided the citation to that paper.
>
> Thanks,
>
> NMF
>
>
>
> "Klenow" <bakedbeans at spam.not> wrote in message
> news:PxiXb.9020$%h1.7659 at fe24.usenetserver.com...
> >
> > I've recently read a paper looking at the effects of 15 minutes of
direct
> > current stimulation (5-15 uA) through a chronic indwelling electrode on
> > kindled seizure thresholds in rats.  Can this type of stimulation cause
an
> > electrolytic lesion at the electrode tip even with such low current?
I've
> > been looking through brain stimulation books and can't find an answer.
> >
> > -- 
> > -----
> >
> >
> >
>
>






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