HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Free Full Text (PDF) Free All Versions of this Article: 102/3/1041    most recent 01148.2006v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science 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 Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Button, D. C. Articles by Gardiner, P. F. Search for Related Content PubMed PubMed Citation Articles by Button, D. C. Articles by Gardiner, P. F.

Spike frequency adaptation of rat hindlimb motoneurons

Spinal Cord Research Center, Department of Physiology, University of Manitoba, Winnipeg, Manitoba, Canada

Submitted 12 October 2006 ; accepted in final form 30 November 2006

The objective of our study was to resolve two issues pertaining to motoneuron (MN) spike frequency adaptation (SFA): 1) to develop an index of SFA that is sensitive to a wide range of adaptation patterns and would correlate well with MN excitability and 2) to determine whether SFA pattern is stimulus current dependent. Sprague-Dawley rats (250–350 g) were anesthetized (ketamine-xylazine) before electrophysiological properties from sciatic nerve MNs located in the lumbar spinal cord were recorded. SFA was measured by 30-s square-wave current injections at 1.5, 3.0, and 5.0 nA above estimated rhythmic firing threshold. Discharges per second were significantly (P < 0.001) higher for 5-nA than for 1.5- and 3-nA currents > rhythmic firing threshold in the first 2 s. SFA was quantified by using ratios of the final to initial number of discharges with 1-, 2-, and 5-s bins. The best index of SFA was the percent decline in the number of spikes fired in the fifth 5-s bin relative to the first 5-s bin [1 – (bin 5/bin 1)]. With the use of this index, we found that SFA was significantly correlated with several measures of MN excitability, including estimated persistent inward current amplitude (r = –0.76) and rheobase current (r = 0.71), and tended to correlate with input resistance (r = –0.43) and frequency-current slope (r = –0.57). This index also showed the widest range of SFA among MNs. In conclusion, an SFA pattern can be ascertained for each MN and becomes more pronounced as MN excitability decreases. Finally, for the first time, we report evidence of a relationship between persistent inward current and SFA.

spinal cord; square-wave pulse injection; persistent inward current

This article has been cited by other articles:

				J. M. Kalmar, D. C. Button, K. Gardiner, F. Cahill, and P. F. Gardiner Caloric Restriction Does Not Offset Age-Associated Changes in the Biophysical Properties of Motoneurons J Neurophysiol, February 1, 2009; 101(2): 548 - 557. [Abstract] [Full Text] [PDF]

				D. C. Button, J. M. Kalmar, K. Gardiner, T. Marqueste, H. Zhong, R. R. Roy, V. R. Edgerton, and P. F. Gardiner Does elimination of afferent input modify the changes in rat motoneurone properties that occur following chronic spinal cord transection? J. Physiol., January 15, 2008; 586(2): 529 - 544. [Abstract] [Full Text] [PDF]