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This Article Full Text Full Text (PDF) All Versions of this Article: 91/5/887    most recent expphysiol.2005.033076v1 Alert me when this article is cited Alert me if a correction is posted 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 Google Scholar Google Scholar Articles by Celichowski, J. Articles by Slawinska, U. Search for Related Content PubMed PubMed Citation Articles by Celichowski, J. Articles by Slawinska, U. Related Collections Muscle

Jan Celichowski¹, Wodzimierz Mrówczyski¹, Piotr Krutki¹, Teresa Górska², Henryk Majczyski² and Urszula Sawiska²

¹ Department of Neurobiology, University School of Physical Education, Poznañ, Poland ² Nencki Institute of Experimental Biology, Warsaw, Poland

The effects of complete transection of the spinal cord at the level of Th9/10 on contractile properties of the motor units (MUs) in the rat medial gastrocnemius (MG) muscle were investigated. Our results indicate that 1 month after injury the contraction time (time-to-peak) and half-relaxation time were prolonged and the maximal tetanic force in most of the MUs in the MG muscle of spinal rats was reduced. The resistance to fatigue also decreased in most of the MUs in the MG of spinal animals. Moreover, the post-tetanic potentiation of twitches in MUs diminished after spinal cord transection. Criteria for the division of MUs into three types, namely slow (S), fast fatigue resistant (FR) and fast fatigable (FF), applied in intact animals, could not be directly used in spinal animals owing to changes in contractile properties of MUs. The ‘sag’ phenomenon observed in unfused tetani of fast units in intact animals essentially disappeared in spinal rats and it was only detected in few units, at low frequencies of stimulation only. Therefore, the MUs in spinal rats were classified as fast or slow on the basis of an adjusted borderline of 20 ms, instead of 18 ms as in intact animals, owing to a slightly longer contraction time of those fast motor units with the ‘sag’. We conclude that all basic contractile properties of rat motor units in the medial gastrocnemius muscle are significantly changed 1 month after complete spinal cord transection, with the majority of motor units being more fatigable and slower than those of intact rats.

(Received 15 December 2005; accepted after revision 18 May 2006; first published online 25 May 2006)
Corresponding author J. Celichowski: Department of Neurobiology, University School of Physical Education, 55 Grunwaldzka Street, 60-352 Poznan, Poland. Email: celichowski{at}awf.poznan.pl