The effect of long-term immobilization on the motor unit population of the cat medial gastrocnemius muscle
| Autor: | Kanda K, Walmsley Bw, J. Toop, R. E. Burke, Hodgson Ja, Mayer Rf |
|---|---|
| Rok vydání: | 1981 |
| Předmět: |
Movement
Population Medial gastrocnemius Isometric exercise Immobilization medicine Animals education Motor Neurons education.field_of_study CATS Electromyography business.industry Muscles General Neuroscience Anatomy musculoskeletal system Muscle atrophy Hindlimb Motor unit medicine.anatomical_structure Cats Excitatory postsynaptic potential Female Ankle medicine.symptom business Muscle Contraction |
| Zdroj: | Neuroscience. 6:725-739 |
| ISSN: | 0306-4522 |
| Popis: | The properties of medial gastrocnemius and soleus muscles and of individual medial gastrocnemius motor units were evaluated after chronic (3–29 weeks) unilateral immobilization of ankle and knee joints in 10 adult female cats. Joint fixation markedly impaired the mobility of the pinned limb and, when prolonged (> 17 weeks; 8 animals), produced marked muscle atrophy and some shortening of whole muscle isometric twitch contraction times (mean contraction time of pinned medial gastrocnemius was 83.3 percent of the contralateral muscle). However, the immobilized muscles were not truly disused, since the patterns of medial gastrocnemius and soleus electromyographic activity during posture and locomotion were qualitatively normal in the 4 animals examined. Despite severe whole muscle atrophy, all but 3 of the 239 individual medial gastrocnemius motor units studied were readily classified into one of the 4 motor unit types (types FF, F(int), FR and S) found in the normal muscle. The histochemical mosaic of immobilized muscles was also the same as in contralateral unoperated muscles. When compared to data from normal cats, there was a highly significant loss of maximum twitch and tetanic force output in all unit types after long-term immobilization (17–29 weeks; N = 187), most marked among the fatigue-resistant unit groups (types FR and S), and mean isometric twitch contraction times were shorter than expected in all unit type groups. The most surprising finding in the present work was that the mean homonymous (medial gastrocnemius) and heteronymous (lateral gastrocnemius-soleus) group Ia excitatory postsynaptic potentials were significantly smaller than expected in all motor unit groups in both short-term and long-term immobilization. The mean axonal conduction velocity of medial gastrocnemius motor axons was unchanged from the normal sample. These results indicate that the essential features that define the motor unit types in normal medial gastrocnemius muscles are resistant to change despite long-term immobilization. We conclude that the motor units types found in normal muscles are robust and essentially unaltered despite severe muscle atrophy. The effects on group Ia excitatory postsynaptic potentials suggest that limb immobilization produces altered patterns of impulse traffic in group Ia afferents that induce significant decreases in synaptic efficacy, although it is unclear whether or not Ia traffic is increased or decreased by immobilization. |
| Databáze: | OpenAIRE |
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