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The Journal of Neuroscience, July 23, 2003, 23(16):6660-6670
Previous Article
Distribution and Properties of Functional Postsynaptic Kainate Receptors on Neocortical Layer V Pyramidal Neurons
Matthias Eder,1
Klaus Becker,1
Gerhard Rammes,1,2
Anja Schierloh,1
Shahnaz Christina Azad,1,3
Walter Zieglgänsberger,1 and
Hans-Ulrich Dodt1
1Clinical Neuropharmacology, Max-Planck-Institute
of Psychiatry, 80804 Munich, Germany, 2Department of
Anesthesiology, Technical University of Munich, 81675 Munich, Germany, and
3Clinic for Anesthesiology, Pain Treatment Unit,
Ludwig-Maximilians-University, 81377 Munich, Germany
The distribution of glutamate receptor subtypes on the surface of neurons
is highly relevant for synaptic transmission and signal processing. In the
present study we investigated the location and properties of functional
kainate receptors (KARs) on the somatodendritic membrane of rat neocortical
layer V pyramidal neurons. Infrared-guided laser stimulation was used to apply
glutamate photolytically to the soma and various sites along the apical
dendrite. Electrical currents, resulting from the activation of
pharmacologically isolated KARs, were measured by whole-cell patch-clamp
recording. In addition, KARs on somatic and dendritic outside-out patches were
activated while still within the brain tissue. We found that functional KARs
are located on the entire somatodendritic membrane that was examined. Fast
kinetics, a linear I-V relationship, and a relatively high
single-channel conductance are characteristic features of these receptors. We
provide evidence that the unitary properties of somatic and dendritic KARs are
identical. Regarding the subcellular distribution of KARs, our results
indicate that the density of these receptors increases toward the distal
dendrite. They are located mainly at extrasynaptic sites but also mediate fast
synaptic signaling triggered by afferent stimulation. The differential
distribution speaks in favor of a selective targeting of KARs on central
neurons and may reflect a mechanism for a location-dependent regulation of
synaptic efficacy. Furthermore, it is feasible to assume that extrasynaptic
KARs could be activated by a "spillover" of synaptically released
glutamate, ambient glutamate in the CSF, or glutamate released from adjacent
astrocytes.
Key words: AMPA receptors; brain slices; caged glutamate; dendrite; distribution; extrasynaptic; kainate receptors; layer V; neocortex; photostimulation; pyramidal neuron; rat; somatosensory; synaptic
Received Apr. 14, 2003;
revised May. 29, 2003;
accepted Jun. 6, 2003.
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