Journal of Comparative Physiology A

, Volume 191, Issue 2, pp 135–146

Afterhyperpolarization–firing rate relation of turtle spinal neurons

  • E. K. Stauffer
  • D. G. Stuart
  • J. C. McDonagh
  • T. G. Hornby
  • R. M. Reinking
Original Paper

DOI: 10.1007/s00359-004-0583-7

Cite this article as:
Stauffer, E.K., Stuart, D.G., McDonagh, J.C. et al. J Comp Physiol A (2005) 191: 135. doi:10.1007/s00359-004-0583-7


This study addressed the afterhyperploarization–firing rate relationship of unanesthetized turtle spinal motoneurons and interneurons. The afterhyperploarization of their solitary action potential at rheobase was compared to that during the cells’ minimum and maximum firing rates. Like previous mammalian findings, afterhyperpolarization duration and area at rheobase were 32 and 19% less for high- versus low-threshold motoneurons. Contrariwise, maximum firing rate was two times less for the high-threshold group. Other new findings were that for high- versus low-threshold interneurons, afterhyperpolarization duration and area were 25 and 95% less, and maximum firing rate 21% higher for the high-threshold group. For combined motoneurons versus interneurons, there were no differences in afterhyperpolarization duration and area at rheobase, whereas maximum firing rate was 265% higher for the interneurons. For high-threshold motoneurons alone, there were significant associations between minimum firing rate and afterhyperpolarization duration and area measured at rheobase. In summary, this study showed that (1) the afterhyperploarization values of both turtle spinal motoneurons and interneurons at rheobase provided little indication of their corresponding values at the cells’ minimum and maximum firing states, and (2) the evolution of afterhyperploarization from rheobase to maximum firing state differed both qualitatively and quantitatively for motoneurons versus interneurons.


Afterhyperpolarization Current–frequency relation Motoneuron Interneuron Turtle spinal cord 





Action potential

f/I slope

Slope of the If relation


Peak AP spike-frequency of If relation


Spike frequency at Imin


High threshold

I-f relation

Stimulus current–spike frequency relation


Stimulus current at fmax


Threshold stimulus current for repetitive AP discharge




Low threshold




Interspike interval

Copyright information

© Springer-Verlag 2004

Authors and Affiliations

  • E. K. Stauffer
    • 1
  • D. G. Stuart
    • 2
  • J. C. McDonagh
    • 3
  • T. G. Hornby
    • 4
  • R. M. Reinking
    • 5
  1. 1.Department of Physiology University of MinnesotaDuluthUSA
  2. 2.Department of Physiology University of ArizonaTucsonUSA
  3. 3.Program in Physical TherapyArizona School of Health SciencesMesaUSA
  4. 4.UIC Department of Physical TherapyChicagoUSA
  5. 5.Program in Applied MathematicsUniversity of ArizonaTucsonUSA

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