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This Article Full Text Full Text (PDF) All Versions of this Article: 101/2/519    most recent 90382.2008v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Diwakar, S. Articles by D'Angelo, E. Search for Related Content PubMed PubMed Citation Articles by Diwakar, S. Articles by D'Angelo, E.

Axonal Na⁺ Channels Ensure Fast Spike Activation and Back-Propagation in Cerebellar Granule Cells

¹Department of Physiological and Pharmacological Sciences, University of Pavia, Pavia, Italy; ²Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, Pavia Unit, Pavia, Italy; ³Department of Mathematics, University of Milan, Milan, Italy; ⁴and Department of Biological Sciences, Hunter College of City University, New York, New York

Submitted 20 March 2008; accepted in final form 19 November 2008

In most neurons, Na⁺ channels in the axon are complemented by others localized in the soma and dendrites to ensure spike back-propagation. However, cerebellar granule cells are neurons with simplified architecture in which the dendrites are short and unbranched and a single thin ascending axon travels toward the molecular layer before bifurcating into parallel fibers. Here we show that in cerebellar granule cells, Na⁺ channels are enriched in the axon, especially in the hillock, but almost absent from soma and dendrites. The impact of this channel distribution on neuronal electroresponsiveness was investigated by multi-compartmental modeling. Numerical simulations indicated that granule cells have a compact electrotonic structure allowing excitatory postsynaptic potentials to diffuse with little attenuation from dendrites to axon. The spike arose almost simultaneously along the whole axonal ascending branch and invaded the hillock the activation of which promoted spike back-propagation with marginal delay (<200 µs) and attenuation (<20 mV) into the somato-dendritic compartment. These properties allow granule cells to perform sub-millisecond coincidence detection of pre- and postsynaptic activity and to rapidly activate Purkinje cells contacted by the axonal ascending branch.