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[Neuroscience] Re: Electrophysiology: monosynaptic vs heterosynaptic transmission.

SJM Guzman jose.guzman at medizin-uni-leipzig.de
Wed Feb 22 13:29:36 EST 2006

Hi R. Norman:

Your explanation was fabulous. I was kind of confuse regarding the 
terminology homosynaptic/monosynpatic. Now is clear to me. Again thank 
you very much.

Regarding the field potential question.... To access the monosynaptic 
component, some laboratories analyze EPSP slopes using the least-squares 
regression. Why not simply to analyze the amplitude?

Here some examples of publications...

"For EPSP analysis, The initial rising slope was measured, (1 msec 
period form its onset, in milivolts per millisencond), which contains 
only a monosynaptic component )..."

"To minimize the contribution of voltage-dependent conductances, initial 
slopes of EPSPs were calculated..."

I would appreciate some literature about it. I miss some about PSC/Ps, 
because traditional electrophysiological books (i.e Hille, Neher & 
Sakmann), don't tell much about it.

Thank you very much again!

SJ Guzman

r norman wrote:

> I think you are confusing two dichotomies.  There is monosynaptic vs.
> multisynaptic referring to the number of sequential synapses in a
> pathway and there is homosynaptic vs. heterosynaptic referring to the
> way that synaptic inputs modulate onto a single cell.  That is, if
> cell A synapses directly on cell B, that is a monosynaptic connection.
> If cell A synapses on cell C which then synapses on cell B, then from
> A to B is disynaptic (or multisynaptic).  I assume that your question
> is about this subject.  Heterosynaptic modulation occurs when cell A
> modifies the way that cell B synapses on cell C.
> In a monosynaptic synapse, an action potential in cell A produces a
> synaptic potential in cell B and there is usually a fixed latency in
> the synaptic potential, as you say.  If the connection between A and B
> is multisynaptic, though, mediated through cell C, then ordinarily
> cell A would have to produce a synaptic potential in cell C strong
> enough to elicit an action potential in C. The action potential in C
> then produces a synaptic potential in B.  There is a fixed latency
> between the action potential in C and the synaptic potential in B (a
> monosynaptic connection) but not between the action potential in A and
> the complex process between the synaptic potential in C and the action
> potential in C.  If the synaptic potential in C is just barely at
> threshold in cell C, it may take some time for the action potential to
> be produced whereas if it is well above threshold, the action
> potential will occur quickly.  And if A is firing at a relatively high
> frequency, it is unlikely that the action potentials in cell C will
> follow one-for-one (unless you have a very unusual "relay" type of
> connection) so that the synaptic potentials in B will not follow the
> action potentials in A one-for-one.  Of course, in a monosynaptic
> connection, the synaptic potentials are always one-for-one with fixed
> latency.
> I am not sure what you mean by the slope of the EPSP/C.  If you mean
> the relation between end plate potential (as measured "normally", i.e.
> during "current" clamp) and the end plate current as measured during
> voltage clamp, that ratio is a measure of the membrane resistance.
> Activation of nearby synapses (i.e. true heterosynaptic effects as
> opposed to multisynaptic ones) can open membrane channels and reduce
> the membrane resistance, causing a synaptic current to generate a
> smaller synaptic potential.  Is that what you mean?


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