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The Journal of Neuroscience, September 28, 2005, 25(39):8917-8923; doi:10.1523/JNEUROSCI.2154-05.2005

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Behavioral/Systems/Cognitive
How Much Afterhyperpolarization Conductance Is Recruited by an Action Potential? A Dynamic-Clamp Study in Cat Lumbar Motoneurons

Marin Manuel, Claude Meunier, Maud Donnet, and Daniel Zytnicki

Neurophysique et Physiologie du Système Moteur, Unité Mixte de Recherche 8119, Centre National de la Recherche Scientifique, and Université René Descartes, 75270 Paris Cedex 06, France

We accurately measured the conductance responsible for the afterhyperpolarization (medium AHP) that follows a single spike in spinal motoneurons of anesthetized cats. This was done by using the dynamic-clamp method. We injected an artificial current in the neurons that increased the AHP amplitude, and we made use of the fact that the intensity of the natural AHP current at the trough of the voltage trajectory was related linearly to the AHP amplitude. We determined at the same time the conductance and the reversal potential of the AHP current. This new method was validated by a simple theoretical model incorporating AHP and hyperpolarization-activated (I_h) currents and could be applied when the decay time constant of the AHP conductance was at least five times shorter than the estimated I_h activation time. This condition was fulfilled in 33 of 44 motoneurons. The AHP conductance varied from 0.3 to 1.4 µS in both slow- and fast-type motoneurons, which was approximately the same range as the input conductance of the entire population. However, AHP and input conductances were not correlated. The larger AHP in slow-type motoneurons was mainly attributable to their smaller input conductance compared with fast motoneurons. The likeness of the AHP conductance in both types of motoneurons is in sharp contrast to differences in AHP decay time and explains why slow- and fast-type motoneurons have similar gain.

Key words: discharge properties; afterhyperpolarizing current; synaptic integration; spinal cord; dynamic clamp; I_h current

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Received May 27, 2005; revised August 8, 2005; accepted August 10, 2005.

This article has been cited by other articles:

				M. Manuel, C. Iglesias, M. Donnet, F. Leroy, C. J. Heckman, and D. Zytnicki Fast Kinetics, High-Frequency Oscillations, and Subprimary Firing Range in Adult Mouse Spinal Motoneurons J. Neurosci., September 9, 2009; 29(36): 11246 - 11256. [Abstract] [Full Text] [PDF]

				A. S. Hyngstrom, M. D. Johnson, and C. J. Heckman Summation of Excitatory and Inhibitory Synaptic Inputs by Motoneurons With Highly Active Dendrites J Neurophysiol, April 1, 2008; 99(4): 1643 - 1652. [Abstract] [Full Text] [PDF]

				M. Manuel, C. Meunier, M. Donnet, and D. Zytnicki Resonant or Not, Two Amplification Modes of Proprioceptive Inputs by Persistent Inward Currents in Spinal Motoneurons J. Neurosci., November 21, 2007; 27(47): 12977 - 12988. [Abstract] [Full Text] [PDF]

				M. Manuel, C. Meunier, M. Donnet, and D. Zytnicki The afterhyperpolarization conductance exerts the same control over the gain and variability of motoneurone firing in anaesthetized cats J. Physiol., November 1, 2006; 576(3): 873 - 886. [Abstract] [Full Text] [PDF]

				J.-M. Goaillard and E. Marder Dynamic Clamp Analyses of Cardiac, Endocrine, and Neural Function Physiology, June 1, 2006; 21(3): 197 - 207. [Abstract] [Full Text] [PDF]

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