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Somatic EPSP amplitude is independent of synapse location in hippocampal pyramidal neurons

Abstract

Most neurons receive thousands of synaptic inputs onto widely spread dendrites. Because of dendritic filtering, distant synapses should have less efficacy than proximal ones. To investigate this, we characterized the amplitude and kinetics of excitatory synaptic input across the apical dendrites of CA1 pyramidal neurons using dual whole-cell recordings. We found that dendritic EPSP amplitude increases with distance from the soma, counterbalancing the filtering effects of the dendrites and reducing the location dependence of somatic EPSP amplitude. Dendritic current injections and a multi-compartmental computer model demonstrated that dendritic membrane properties have only a minor role in elevating the local EPSP. Instead a progressive increase in synaptic conductance seems to be primarily responsible for normalizing the amplitudes of individual inputs.

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Figure 1: Synaptically evoked EPSP amplitude at the soma is independent of synapse location.
Figure 2: The somatic amplitude of EPSPs generated by uniform current injections depends on input location.
Figure 3: Location and amplitude dependence of EPSP kinetics.
Figure 4: An increase in synaptic conductance can account for the normalization of somatic EPSP amplitude in a passive computer model.
Figure 5: Dendritic EPSC amplitude increases with synapse distance.
Figure 6: Location and amplitude dependence of EPSC kinetics.
Figure 7: Amplitude of smallest dendritic events shows little dependence on synapse location.

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Acknowledgements

We thank M. Carruth for technical assistance, M. Vollrath for comments on the manuscript and D. Johnston for discussions throughout the study. This work was supported by National Institute of Health grants NS35865 and NS39458 and by the Alfred P. Sloan Foundation.

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Correspondence to Jeffrey C. Magee.

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Magee, J., Cook, E. Somatic EPSP amplitude is independent of synapse location in hippocampal pyramidal neurons. Nat Neurosci 3, 895–903 (2000). https://doi.org/10.1038/78800

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