The Journal of Neuroscience, April 1, 2000, 20(7):2451-2458
Synaptic Activity Modulates the Induction of Bidirectional
Synaptic Changes in Adult Mouse Hippocampus
Anaclet
Ngezahayo1,
Melitta
Schachner1, 2, and
Alain
Artola1
1 Department of Neurobiology, Swiss Federal Institute
of Technology Zürich, Hönggerberg, CH-8093 Zürich,
Switzerland, and 2 Zentrum für Molekulare
Neurobiologie, Universität Hamburg, D-20246 Hamburg,
Germany
Activity-dependent synaptic plasticity is critical for learning and
memory. Considerable attention has been paid to mechanisms that
increase or decrease synaptic efficacy, referred to as long-term potentiation (LTP) and long-term depression (LTD), respectively. It is
becoming apparent that synaptic activity also modulates the ability to
elicit subsequent synaptic changes. We provide direct experimental
evidence that this modulation is attributable, at least in part,
to variations in the level of postsynaptic depolarization required for
inducing plasticity. In slices from adult hippocampal CA1, a brief
pairing protocol known to produce LTP can also induce LTD. The
voltage-response function for the induction of LTD and LTP in naive
synapses exhibits three parts: at a postsynaptic membrane potential
during pairing (Vm) 
40 mV,
no synaptic modification is obtained; at Vm
between 40 and 20 mV, LTD is induced; and, finally, at
Vm > 20 mV, LTP is generated. This
function varies with initial synaptic efficacy. In depressed synapses,
, the Vm above which LTD is
generated, is shifted toward more depolarized
Vms and +, the LTD-LTP
crossover point or, equivalently, the Vm
above which LTP is induced, toward more polarized
Vms. Conversely in potentiated synapses,
is shifted toward more polarized
Vms. Therefore synaptic activity changes
synaptic efficacy and accordingly adjusts the voltages for eliciting
subsequent synaptic modifications. The concomitant shifts in the
voltages for inducing LTD and LTP in opposite directions promote
synaptic potentiation and inhibit synaptic depression in depressed
synapses and vice versa in potentiated synapses.
Key words:
long-term potentiation; long-term depression; activity-dependent modulation of LTD-LTP induction; hippocampus; CA1; mouse
Copyright © 2000 Society for Neuroscience 0270-6474/00/2072451-08$05.00/0
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