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NMDA Receptor-Mediated Currents in Rat Cerebellar Granule and Unipolar Brush Cells
Department of Physiology and Institute for Neuroscience, Northwestern University Medical School, Chicago, Illinois 60611 Billups, Daniela, Ying-Bing Liu, Susanne Birnstiel, and N. Traverse Slater. NMDA Receptor-Mediated Currents in Rat Cerebellar Granule and Unipolar Brush Cells. J. Neurophysiol. 87...
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Published in: | Journal of neurophysiology 2002-04, Vol.87 (4), p.1948-1959 |
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Main Authors: | , , , |
Format: | Article |
Language: | English |
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Online Access: | Get full text |
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Summary: | Department of Physiology and Institute for Neuroscience,
Northwestern University Medical School, Chicago, Illinois 60611
Billups, Daniela,
Ying-Bing Liu,
Susanne Birnstiel, and
N. Traverse Slater.
NMDA Receptor-Mediated Currents in Rat Cerebellar Granule and
Unipolar Brush Cells. J. Neurophysiol. 87: 1948-1959, 2002. The properties of
N -methyl- D -aspartate (NMDA) receptor-mediated
currents at the giant cerebellar mossy-fiber unipolar brush cell (UBC)
synapse were compared with those of adjacent granule cells using
patch-clamp recording methods in thin slices of rat cerebellar nodulus.
In UBCs, NMDA receptor-mediated excitatory postsynaptic currents
(EPSCs) decayed as a single exponential whose time constant was
independent of membrane potential. The EPSC was reduced in all cells by
the NR1/NR2B-selective antagonist ifenprodil, and the
Zn 2+ chelator
N,N,N',N' -tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) produced a transient potentiation in 50% of cells. In contrast, the
NMDA EPSC in granule cells decayed as a double exponential that
dramatically switched to a slower rate at positive membrane potentials.
The synaptic response in some granule cells also displayed a late
second peak at positive potentials, and in others, activation of mossy
fibers produced repetitive trains of EPSCs indicating they may be
postsynaptic to the UBC network. Single-channel recordings of
outside-out somatic patches from UBCs in magnesium-free solution revealed only high-conductance (50 pS) channels whose open time was
increased with depolarization, but the opening frequency was decreased
to yield a low ( p o = 0.0298),
voltage-independent opening probability. Lowering extracellular calcium
(2.5-0.25 mM) had no effects on channel gating, although an increase
of single-channel conductance was observed at lower calcium
concentrations. Taken together, the data support the notion that the
NMDA receptor in UBCs may comprise both NR1/NR2A and NR1/NR2B
receptors. Furthermore, the properties of the EPSC in these two classes
of feedforward glutamatergic interneurons display fundamental
differences that may relate to their roles in synaptic integration. |
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ISSN: | 0022-3077 1522-1598 |
DOI: | 10.1152/jn.00599.2001 |