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The Journal of Neuroscience, February 15, 2002, 22(4):1199-1207
Pathway-Specific Properties of AMPA and NMDA-Mediated
Transmission in CA1 Hippocampal Pyramidal Cells
Nonna A.
Otmakhova,
Nikolai
Otmakhov, and
John E.
Lisman
Department of Biology and Volen Center for Complex Systems,
Brandeis University, Waltham, Massachusetts 02454
CA1 pyramidal cells receive glutamatergic input from the entorhinal
cortex through the perforant path (PP) and from CA3 through Schaffer
collaterals (SC). The PP input terminates in the stratum lacunosum
moleculare ~300 µm from the cell body, whereas SC synapses have a
more proximal location in the stratum radiatum. We compared the
properties of AMPA- and NMDA-mediated transmission at these two inputs.
The AMPA-mediated components have linear voltage dependence in both
inputs. The reversal potential in the PP is only slightly more positive
than in the SC, indicating that distal membrane voltage could be
effectively set. The NMDA-mediated responses in the two pathways,
however, are very different. The PP exhibits inward rectification, as
evidenced by very low outward currents. The rectification persists in
the absence of extracellular Mg2+. It cannot be
attributed to clamping problems, because large outward AMPA currents
can be observed even when conditions are modified to have the AMPA
currents kinetically match the NMDA currents. Thus, it appears that the
PP NMDA channels have novel properties. A second difference between the
PP and SC pathways is that the PP has a larger NMDA/AMPA charge ratio.
This difference could be observed under many conditions, including
block of all voltage-dependent conductances and elimination of the
negative resistance of NMDA channels by removing extracellular
Mg2+. The difference in ratio thus cannot be
attributed to regenerative currents. The higher NMDA component of the
distal PP synapses could help to make these synapses more powerful
under depolarizing conditions.
Key words:
AMPA; CA1; D890; inward rectification; NMDA; perforant
path; QX-314; regenerative process; Schaffer collaterals; voltage
dependence; whole-cell patch clamp; ZD7288
Copyright © 2002 Society for Neuroscience 0270-6474/02/2241199-09$05.00/0
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