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LTP and post-tetanic potentiation

Matt Jones jonesmat at ohsu.edu
Wed Apr 7 15:09:36 EST 1999

In article <370a08ca.3760457 at news.ox.ac.uk> Grushnik,
james.teo at chch.ox.ac.uk writes:
>If I am correct this prime burst
>potentiation is still quite unphysiological.

The primed-burst protocol is about as physiological as you can get if
you're stimulating several axons synchronously (which may or may not be
what happens in the brain).

The idea is this: there are GABA-B receptors on inhibitory terminals,
that sense the GABA released by the last stimulus, and down-regulate the
release probability on the next stimulus. The window over which these
receptors remains active is about 100 -1000 ms, with a peak of the effect
at about 200 ms. Notice that this spans the range of the hippocampal
theta rhythm (~2-7 Hz). So you give a spike, that triggers both
excitation and feed-forward inhibition, but the inhibition will be
down-regulating itself for about 1sec. If you give a brief burst (which
is the preferential mode of CA3 firing) during this period, inhibition is
not very effective and you can drive the CA1 cells very strongly. 

So this allows you to get LTP by using frequencies and patterns that are
already going on in the hippocampus (where it's most often studied). The
caveat is that it probably doesn't work very well at all if you're only
stimulating a single axon, because that can't usually drive a spike
anyway in CA1 cells.

Matt Jones

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