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The Journal of Neuroscience, October 7, 2009, 29(40):12641-12652; doi:10.1523/JNEUROSCI.1124-09.2009

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Cellular/Molecular
Properties of Piriform Cortex Pyramidal Cell Dendrites: Implications for Olfactory Circuit Design

Brice Bathellier,¹ Troy W. Margrie,² and Matthew E. Larkum¹

¹Department of Physiology, University of Bern, CH-3012 Bern, Switzerland, and ²Department of Neuroscience, Physiology, and Pharmacology, University College London, London WC1E 6BT, United Kingdom

Correspondence should be addressed to Matthew E. Larkum, Department of Physiology, University of Bern, Bühlplatz 5, CH-3012 Bern, Switzerland. Email: larkum{at}pyl.unibe.ch

Unlike the neocortex, sensory input to the piriform cortex is anatomically segregated in layer 1, making it ideal for studying the dendritic integration of synaptic inputs pivotal for sensory information processing. Here we investigated dendritic integration of olfactory bulb inputs in pyramidal cells using dual patch-clamp recordings along the soma–apical dendritic axis. We found that these dendrites are relatively compact with 50% maximal somatic current loss for synaptic inputs arriving at distal dendritic regions. Distal dendrites could generate small and fast local spikes, but they had little impact on the soma, indicating that they are only weakly active. In contrast to the neocortex, we found no evidence for dendritic Ca²⁺ or NMDA spikes though these dendrites actively supported action potential backpropagation with concomitant entry of Ca²⁺ ions. Based on experiments and simulations we suggest that regardless of dendritic location, olfactory bulb inputs have nearly uniform potency and are distributed diffusely over the distal apical tree (layer Ia), thereby minimizing sublinear summation effects. This indicates that any stimulus feature extraction performed by these cells will occur at the soma and is based on the nearly linear sum of olfactory bulb inputs, rather than on explicitly designed clusters of functionally related synapses in the dendritic tree.

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Received March 5, 2009; revised Aug. 5, 2009; accepted Aug. 9, 2009.

Correspondence should be addressed to Matthew E. Larkum, Department of Physiology, University of Bern, Bühlplatz 5, CH-3012 Bern, Switzerland. Email: larkum{at}pyl.unibe.ch

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