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Science 311 (5758): 233-235

Copyright © 2006 by the American Association for the Advancement of Science

Excitatory Effect of GABAergic Axo-Axonic Cells in Cortical Microcircuits

János Szabadics,1* Csaba Varga,1* Gábor Molnár,1* Szabolcs Oláh,1 Pál Barzó,2 Gábor Tamás1{delta}

Abstract: Axons in the cerebral cortex receive synaptic input at the axon initial segment almost exclusively from {gamma}-aminobutyric acid–releasing (GABAergic) axo-axonic cells (AACs). The axon has the lowest threshold for action potential generation in neurons; thus, AACs are considered to be strategically placed inhibitory neurons controlling neuronal output. However, we found that AACs can depolarize pyramidal cells and can initiate stereotyped series of synaptic events in rat and human cortical networks because of a depolarized reversal potential for axonal relative to perisomatic GABAergic inputs. Excitation and signal propagation initiated by AACs is supported by the absence of the potassium chloride cotransporter 2 in the axon.

1 Department of Comparative Physiology, University of Szeged, Közèp fasor 52, Szeged, H-6726, Hungary.
2 Department of Neurosurgery, University of Szeged, Közèp fasor 52, Szeged, H-6726, Hungary.

* These authors contributed equally to this work.

{delta} To whom correspondence should be addressed. E-mail: gtamas{at}

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