The Journal of Neuroscience, January 1, 2003, 23(1):112-121
Differential Effects of Short- and Long-Term Potentiation on Cell
Firing in the CA1 Region of the Hippocampus
Carrie P.
Marder and
Dean V.
Buonomano
Departments of Neurobiology and Psychology, and Brain Research
Institute, University of California, Los Angeles, Los Angeles,
California 90095
Long-term potentiation (LTP) in the hippocampus enhances the
ability of a stimulus to produce cell firing, not only by increasing the strength of the EPSPs, but also by increasing the efficiency of the
input/output (I/O) function of pyramidal neurons. This means that EPSPs
of a given size more easily elicit spikes after LTP, a process known as
EPSP-spike (E-S) potentiation. In contrast to LTP, it is not known
whether the synaptic strengthening produced by paired-pulse
facilitation (PPF) also results in changes in the I/O function. We have
addressed this question by examining E-S curves from rat hippocampal
area CA1 in response to both PPF and LTP. We describe a novel form of
I/O modulation in which PPF produces E-S depression; that is, the E-S
curve is shifted to the right, indicating a decreased ability of EPSPs
to elicit action potentials. Consistent with the notion that E-S
potentiation observed with LTP is caused by long-term increases in the
excitatory-inhibitory ratio, we show that PPF-induced E-S
depression relies on short-term decreases in this ratio. These results
indicate that different forms of synaptic plasticity that produce the
same degree of EPSP potentiation can result in dramatically different
effects on cell firing, because of the dynamic changes in the
excitatory-inhibitory balance within local circuits.
Key words:
hippocampus; CA1; inhibition; EPSP-spike
potentiation; long-term potentiation; paired-pulse facilitation; input/output; circuit
Copyright © 2003 Society for Neuroscience 0270-6474/03/231112-10$05.00/0
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