AMPA/NMDA and GABAa/GABAb conductance ratios

Matt Jones jonesmat at physiology.wisc.edu
Thu Sep 19 13:30:03 EST 2002


"John H." <johnhkm at overhere.com.au> wrote in message news:<Fm2i9.6213$Sr6.220414 at ozemail.com.au>...
> Any ideas on what causes the receptor ratio shift??? 

Supposedly, it is insertion of a standby pool of AMPA receptors into
the synaptic membrane. People are still arguing about this (of
course).


>Maybe silent synapses
> is inhibition without inhibitory agents, a way of preventing too much
> activity prior to the establishment of 'working synapses' 

Actually, the synapses are not really silent. They have NMDA EPSCs,
just not AMPA  EPSCs. They -look- silent in a voltage-clamp recording
if the cell is held at -60 (which is a typical thing to do in such a
recording), but when they're depolarized the NMDA EPSC becomes obvious
(because the depolarization relieves the Mg block of NMDA receptors).

After an LTP-inducing  stimulus , suddenly the AMPA EPSC appears. 

As far as I know, few people have tried to study this in
current-clamp, where the membrane potential can go wherever it wants.
These synapses are likely to contribute to the normal behavior, even
while they are "silent" at the resting potential. For example, during
a spike, or an EPSP generated at a neighboring non-silent synapse, the
NMDA component of the silent synapses will wake from its dogmatic
slumber and contribute a further depolarizing influence (as well as
belching calcium all over the place).

Since this seems to have something to do with LTP, that explains why
it's such a sexy topic all of a sudden, and also why nobody can agree
about how it works (apologies to my "excitatory" colleagues - I just
can't help myself).




> 
> Unfortunately God is not going to help us at all. This ng may as well
> receive the last rites.

Oh, I've been reading this group long enough to know that it'll
eventually return to"normal" (oooh, I shiver with
antici..........pation ).  There have been many of these plagues of
irrelevant crossposts in the past (do you remember the perennial
"Aspartame is the devil's messenger" threads). This one is exceedingly
bad, but these people aren't to be taken seriously. They'll ultimately
get bored and go find somewhere else to play.

Cheers,

Matt



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