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[Neuroscience] Re: EPSP slope

r norman via neur-sci%40net.bio.net (by r_s_norman from _comcast.net)
Mon Jan 7 11:02:19 EST 2008


On Mon, 07 Jan 2008 15:44:12 +0100, SJM Guzman
<jose.guzman from medizin.uni-leipzig.de> wrote:

>Hello All 
>I am trying to calculate the EPSP slope in the 2 ms period from the EPSP 
>onset. This value is known to give a measure of the synaptic strength, 
>because it contains only the monosynaptic component of the EPSP. 
>
>My question is why is the monosynaptic component related with the synaptic 
>strength (i.e. up/down-regulations of receptors). 
>
>On the other hand, given the kinetics of the EPSP, wouldn't it be more 
>correct to fit the initial component of the EPSP with a monoexponential 
>function and obtain the exponential coefficient as a mesure of the initial 
>EPSP component? 
>
>Thank you very much in advance! 
>

It has been some time since I did this stuff so there may be newer
interpretations.

My impression is that the epsp slope gives a better measure of the
synaptic strength than the amplitude because it is a more direct
measure of synaptic current which is mostly capacitative current, Ic =
C dV/dt.  That is, in the non-synaptic membrane; the ionic synaptic
current completes its loop through the non-synaptic membrane as
capacitative current.  And synaptic current is a direct measure of the
opening of synaptic channels.

The notion of connecting this to monosynaptic connections seems
strange.  A polysynaptic connection through serial synapses would have
no effect on the final synaptic step, which is the only one you
measure.  If you mean parallel synaptic connections, then if more than
one synapse fires simultaneously, you would never see it.  However if
there is a time delay between them then you might be able to see
multiple peaks in the current -- that is, in the slope.


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