Q: how to distinguish pre- or postsynaptic inhibition?

Richard Vickery Richard.Vickery at unsw.edu.au
Tue Aug 8 20:47:48 EST 2000

Kung-Chiao Hsieh wrote:
> Just wandering how neurophysiologists can tell the inhibition occurs
> presynaptically or postsynaptically from the recording electrodes. Can
> they?

This depends upon your recording technique etc.
If you have access to the cell's interior (patch clamping or
sharp electrode) then a post-synaptic inhibition will show up as
an inhibitory potential (negative potential) whereas pre-synaptic
inhibition will not show up as a postsynaptic current.  You may
have to test the cell at a series of holding potentials to see
the current.

Alternatively you can use pharmacology to help as postsynaptic
inhibiton is usually GABA-A mediated and blocked by bicuculline
whereas presynaptic inhib is usually GABA-B mediatedand blocked
by phaclofen.

There are plenty of other tricks, many more indirect but which
can lead to a reasonably safe conclusion.

Dr Richard Vickery                  
School of Physiology & Pharmacology, UNSW, Australia, 2052
ph. 61 2 93851676,  fax 61 2 93851059              

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