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NEUROSCIENCE |
1 Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, VA, USA
2
Center for Learning and Memory, University of Texas, Austin, TX, USA
Back-propagating action potentials (bAPs) travelling from the soma to the dendrites of neurons are involved in various aspects of synaptic plasticity. The distance-dependent increase in Kv4.2-mediated A-type K+ current along the apical dendrites of CA1 pyramidal cells (CA1 PCs) is responsible for the attenuation of bAP amplitude with distance from the soma. Genetic deletion of Kv4.2 reduced dendritic A-type K+ current and increased the bAP amplitude in distal dendrites. Our previous studies revealed that the amplitude of unitary Schaffer collateral inputs increases with distance from the soma along the apical dendrites of CA1 PCs. We tested the hypothesis that the weight of distal synapses is dependent on dendritic Kv4.2 channels. We compared the amplitude and kinetics of mEPSCs at different locations on the main apical trunk of CA1 PCs from wild-type (WT) and Kv4.2 knockout (KO) mice. While wild-type mice showed normal distance-dependent scaling, it was missing in the Kv4.2 KO mice. We also tested whether there was an increase in inhibition in the Kv4.2 knockout, induced in an attempt to compensate for a non-specific increase in neuronal excitability (after-polarization duration and burst firing probability were increased in KO). Indeed, we found that the magnitude of the tonic GABA current increased in Kv4.2 KO mice by 53% and the amplitude of mIPSCs increased by 25%, as recorded at the soma. Our results suggest important roles for the dendritic K+ channels in distance-dependent adjustment of synaptic strength as well as a primary role for tonic inhibition in the regulation of global synaptic strength and membrane excitability.
(Received 19 March 2008;
accepted after revision 16 June 2008;
first published online 19 June 2008)
Corresponding author B. K. Andrásfalvy: HHMI, Janelia Farm Research Campus, 19700 Helix Drive, Ashburn, VA 20147, USA. Email: andrasfalvyb{at}janelia.hhmi.org
Related Article
J. Physiol. 2008 586: 3731-3732.
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  D. Hoffman Firing first: compensatory changes in K+ channel knockout mice preserve excitability but not synaptic scaling J. Physiol., August 15, 2008; 586(16): 3731 - 3732. [Full Text] [PDF]
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