Targeted dendrotomy reveals active and passive contributions of the dendritic tree to synaptic integration and neuronal output

doi:10.1073/pnas.0701586104

Targeted dendrotomy reveals active and passive contributions of the dendritic tree to synaptic integration and neuronal output

John M. Bekkers*,^†,^‡ and
Michael Häusser^‡,^§

*Division of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra ACT 0200, Australia; and
^‡Wolfson Institute for Biomedical Research and
^§Department of Physiology, University College London, Gower Street, London WC1E 6BT, United Kingdom

Edited by Charles F. Stevens, The Salk Institute for Biological Studies, La Jolla, CA, and approved May 17, 2007 (received for review February 21, 2007)

Abstract

Neurons typically function as transduction devices, converting patterns of synaptic inputs, received on the dendrites, into trains of output action potentials in the axon. This transduction process is surprisingly complex and has been proposed to involve a two-way dialogue between axosomatic and dendritic compartments that can generate mutually interacting regenerative responses. To manipulate this process, we have developed a new approach for rapid and reversible occlusion or amputation of the primary dendrites of individual neurons in brain slices. By applying these techniques to cerebellar Purkinje and layer 5 cortical pyramidal neurons, we show directly that both the active and passive properties of dendrites differentially affect firing in the axon depending on the strength of stimulation. For weak excitation, dendrites act as a passive electrical load, raising spike threshold and dampening axonal excitability. For strong excitation, dendrites contribute regenerative inward currents, which trigger burst firing and enhance neuronal excitability. These findings provide direct support for the idea that dendritic morphology and conductances act in concert to regulate the excitability of the neuron.

Footnotes

^†To whom correspondence should be addressed. E-mail: John.Bekkers{at}anu.edu.au
Author contributions: J.M.B. and M.H. designed research; J.M.B. performed research; J.M.B. analyzed data; J.M.B. and M.H. wrote the paper; and J.M.B. and M.H. performed modeling.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Abbreviations:

ADP,

afterdepolarization;

AHP,

afterhyperpolarization;

AP,

action potential;

f-I plot,

plot of AP frequency versus current step amplitude.