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Myoneural interactions affect diaphragm muscle adaptations to inactivity
H Miyata1, W Z Zhan, Y S Prakash
1Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota 55905, USA.
Journal of Applied Physiology (Bethesda, Md. : 1985)
|November 1, 1995
Summary
Diaphragm muscle inactivity effects are reduced when both muscle fibers and motoneurons are inactive. Matching these inactive states in rats attenuated muscle adaptations to inactivity.
Area of Science:
- Physiology
- Muscle Biology
- Neuroscience
Background:
- Prolonged inactivity leads to diaphragm muscle dysfunction.
- The role of phrenic motoneuron activity in mediating these changes is not fully understood.
Purpose of the Study:
- To investigate how simultaneous phrenic motoneuron and diaphragm muscle inactivity affects muscle properties.
- To compare the effects of different inactivity models on diaphragm contractile and morphometric characteristics.
Main Methods:
- Three rat diaphragm inactivity models were used: spinal isolation, tetrodotoxin (TTX) nerve blockade, and denervation (Dnv).
- Contractile force, fatigue resistance, and fiber type proportions/cross-sectional areas were assessed after 2 weeks.
Main Results:
- Maximum tetanic force decreased in all groups, with greater reductions in TTX and Dnv groups.
- Fatigue resistance improved and shortening velocity slowed only in TTX and Dnv groups.
- Specific fiber type adaptations (hypertrophy/atrophy) varied across groups, with significant changes in TTX and Dnv.
Conclusions:
- Muscle adaptations to inactivity are attenuated when both muscle fibers and motoneurons are simultaneously inactive.
- Matching motoneuron and muscle inactivity (spinal isolation model) resulted in less severe diaphragm dysfunction compared to nerve blockade or denervation.