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Excitability of cortical neurons depends upon a powerful tonic conductance in inhibitory networks

Published online by Cambridge University Press:  19 January 2007

Esther I. Krook-Magnuson  and
Molly M. Huntsman
Esther I. Krook-Magnuson
Affiliation:
Dept of Pharmacology and Interdisciplinary Program in Neuroscience, Georgetown University Medical Center, USA
Molly M. Huntsman
Affiliation:
Dept of Pharmacology and Interdisciplinary Program in Neuroscience, Georgetown University Medical Center, USA
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Abstract

Layer 4 of the mouse somatosensory (barrel) cortex has a diversity of interneuron cell types. Tonic inhibition in other regions is cell type-specific and mediated, in part, by δ-subunit containing, extrasynaptic, GABAA receptors. We have investigated tonic inhibition in LTS cells, a major type of inhibitory neuron, and excitatory cells in layer 4 of the mouse barrel cortex using 4,5,6,7-tetrahydroisothiazolo-[5,4-c]pyridine-3-ol (THIP), a superagonist of these receptors. Bath application of 20 µM THIP produced baseline shifts, which indicates activation of tonic inhibition of both excitatory and LTS cells. The baseline shift was significantly larger in LTS cells. This finding of greater induced current in LTS cells was paralleled by a significantly greater increase in conductance with THIP application in LTS cells. The increase in conductance resulted in LTS cells requiring more current to reach threshold. Because of the differential effects of tonic inhibition on LTS cells and excitatory cells, bath application of THIP increased the network excitability, measured by multi-unit recordings. Thus, the network effect of tonic inhibition in horizontal layer 4 circuits is a paradoxical increase in excitation.

Keywords

barrelsomatosensoryTHIPtonic inhibitioninterneurons
Type
Research Article
Information
Thalamus & Related Systems , Volume 3 , Issue 2 , June 2005 , pp. 115 - 120
Copyright
© 2007 Cambridge University Press

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