DC lesion?

NMF nm_fournier at ns.sympatico.ca
Sat Feb 14 01:23:44 EST 2004


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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