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This Article Full Text Full Text (PDF) Supplemental data All Versions of this Article: 576/3/873    most recent jphysiol.2006.117002v2 jphysiol.2006.117002v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Manuel, M. Articles by Zytnicki, D. Search for Related Content PubMed PubMed Citation Articles by Manuel, M. Articles by Zytnicki, D. Related Collections Integrative

¹ Laboratoire de Neurophysique et Physiologie, UMR 8119, CNRS and Université René Descartes, 45 rue des Saints-Pères, 75270 Paris Cedex 06, France

Does the afterhyperpolarization current control the gain and discharge variability of motoneurones according to the same law? We investigated this issue in lumbar motoneurones of anaesthetized cats. Using dynamic clamp, we measured the conductance, time constant and driving force of the AHP current in a sample of motoneurones and studied how the gain was correlated to these quantities. To study the action of the AHP on the discharge variability and to compare it to its action on the gain, we injected an artificial AHP-like current in motoneurones. This increased the natural AHP. In three motoneurones, we abolished most of the natural AHP with the calcium chelator BAPTA to investigate the condition where the discharge was essentially controlled by the artificial AHP. Our results demonstrate that both the gain and the coefficient of variation of the firing rate are inversely proportional to the magnitude and to the time constant of the artificial AHP conductance. This indicates that the AHP exerts the same control over the gain and the variability. This mechanism ensures that the variability of the discharge is modulated with the gain. This guarantees a great regularity of the discharge when the motoneurone is in a low excitability state and hence good control of the force produced.

(Received 13 July 2006; accepted after revision 17 August 2006; first published online 24 August 2006)
Corresponding author D. Zytnicki: Laboratoire de Neurophysique et Physiologie, UMR 8119, CNRS and Université René Descartes, 45 rue des Saints-Pères, 75270 Paris Cedex 06, France. Email: daniel.zytnicki{at}univ-paris5.fr

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