The Journal of Neuroscience, November 1, 2001, 21(21):8362-8369
Paired-Pulse Plasticity at the Single Release Site Level: An
Experimental and Computational Study
Eric
Hanse and
Bengt
Gustafsson
Institute of Physiology and Pharmacology, Göteborg
University, SE-405 30 Göteborg, Sweden
CA3-CA1 glutamatergic synapses in the hippocampus exhibit a large
heterogeneity in release probability (p)
and paired-pulse (PP) plasticity, established already in the early
neonatal period when the CA3-CA1 connections consist of only a single
release site. At such a site two factors decide initial release
probability: the number of immediately releasable vesicles (preprimed
pool) and the vesicle release probability
(Pves1). Depletion and replenishment of this pool, an alteration in Pves,
and desensitization of postsynaptic receptors may contribute to PP
plasticity. A model based on data from single neonatal CA3-CA1
synapses has been used to address the relative importance of these
factors for the heterogeneity in PP plasticity. At a 20 msec PP
interval, the PP ratio
(P2/P1) varied from 0.1 to 4.5 among the synapses. At this interval
desensitization and replenishment were of little importance. The
heterogeneity was explained mostly by the variation in
Pves1, whereas the preprimed pool
size was of minor importance. Pves altered
from the first to the second stimulus such that
Pves2 was rather uniform among the synapses.
Its variation thus contributed little to the heterogeneity in PP ratio.
The model also shows that the relationship between alterations in
release probability and PP ratio is complex. Thus, an increase in
release probability can be associated with an increase, a decrease, or
no change at all in PP ratio, depending on the original values of
Pves1 and the preprimed pool and on which
one of these factors is altered to produce the increase in release probability.
Key words:
paired pulse; release probability; hippocampus; CA1; synaptic plasticity; development
Copyright © 2001 Society for Neuroscience 0270-6474/01/21218362-08$05.00/0