Two Paired-Pulse Facilitation Questions

Stephen Maren maren at
Fri Mar 1 10:39:52 EST 1996

> Is anyone of you aware of any references dealing with the physiological role 
> of PPF in neuronal and synaptic function ? 

I suggest looking at Zucker's (1989?) Ann. Rev. Neurosci. paper on
short-term synaptic plasticity.

> Also, it has been showed that PPF 
> changes in a rather complicated manner after the induction of LTP, and I 
> wandered if there are any references dealing with the role of this influence 
> in synaptic plasticity.

You're right, PPF does change following LTP induction, but this effect
appears to be restricted to mossy fiber synapses in hippocampal area CA3
(I've also found synapses in the amygdala that appear to exhibit decreased
PPF following LTP induction; Maren & Fanselow (1995), J. Neurosci.,
15:7548-64).  There is no good evidence that LTP in hippocampal area CA1
is associated with a change in PPF, and the situation in the dentate gyrus
may depend on the afferent pathway (medial vs. lateral perforant path)
that is stimulated.  (Nicoll has a good deal of work on PPF and LTP
induction in CA3 vs. CA1).  The reductions in PPF following mossy fiber
LTP induction have been used as evidence for an increase in presynaptic
transmitter release probablity (Pr) following LTP induction.  The notion
is that insofar as LTP involves a change in Pr, it should be associated
with a change in PPF, because PPF is sensitive to a wide variety of
manipulations that change Pr.  The absence of a change in PPF in CA1 has
bolstered the view that LTP may be mediated by a postsynaptic change (Liao
et al., 1995, Nature), possibly by an increase in the number of
postsynaptic AMPA receptors (Maren et al., 1993, PNAS 90:9654-9658).  

Hope this helps...

S. Maren

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