[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 
you very much.

component, some laboratories analyze EPSP slopes using the least-squares 
regression. Why not simply to analyze the amplitude?

Here some examples of publications...

only a monosynaptic component )..."

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

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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