Mechanical and morphological properties of chronically inactive cat tibialis anterior motor units.

Pierotti, David J.; Roy, Roland R.; Bodine, Sue C.; Hodgson, John A.; Edgerton, V. Reggie

doi:10.1113/jphysiol.1991.sp018872

Cited by 76 publications

(59 citation statements)

References 38 publications

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“…The majority of previous studies have focused on the role of activation levels in maintaining or modifying muscle mass and phenotype through perturbations of normal activity (Edgerton and Roy, 1996;Grossman et al, 1998;Lewis et al, 1997;Pette and Vrbova, 1999;Pierotti et al, 1991;Roy et al, 1991c;Salmons and Sreter, 1976;Windsich et al, 1998). However, a number of observations demonstrate that the level of activation alone does not determine either normal muscle mass or phenotype Pette et al, 1992).…”

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confidence: 94%

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Does daily activity level determine muscle phenotype?

Hodgson

Roy

Higuchi

et al. 2005

Journal of Experimental Biology

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SUMMARY The activation level of a muscle is presumed to be a major determinant of many mechanical and phenotypic properties of its muscle fibers. However, the relationship between the daily activation levels of a muscle and these properties has not been well defined, largely because of the lack of accurate and sustained assessments of the spontaneous activity levels of the muscle. Therefore, we determined the daily activity levels of selected rat hindlimb muscles using intramuscular EMG recordings. To allow comparisons across muscles having varying activity levels and/or muscle fiber type compositions,we recorded EMG activity in a predominantly slow plantarflexor (soleus), a predominantly fast plantarflexor (medial gastrocnemius, MG), a predominantly fast ankle dorsiflexor (tibialis anterior, TA) and a predominantly fast knee extensor (vastus lateralis, VL) in six unanesthetized rats for periods of 24 h. EMG activity levels were correlated with the light:dark cycle, with peak activity levels occurring during the dark period. The soleus was the most active and the TA the least active muscle in all rats. Daily EMG durations were highest for soleus (11–15 h), intermediate for MG (5–9 h) and VL (3–14 h) and lowest for TA (2–3 h). Daily mean EMG amplitudes and integrated EMG levels in the soleus were two- to threefold higher than in the MG and VL and seven- to eightfold higher than in the TA. Despite the three- to fourfold difference in activation levels of the MG and VL vs the TA, all three predominantly fast muscles have been reported to have a similar, very low percentage of slow fibers. Comparing these relative EMG levels to the published fiber type profiles of these muscles yields a very poor relationship between daily activity level and fiber type composition in the same muscles across several species. Although it is clear that changing the levels of activity can modulate the expression of the myosin phenotype,these results indicate that factors other than activation must play critical roles in determining and maintaining normal phenotypic properties of skeletal muscle fibers.

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mentioning

confidence: 94%

“…For other muscles containing slow fibers, such as the tibialis anterior (TA) in cats and Rhesus monkeys, even the most recruited motor units appear to be active for less than 1·h·day -1 , suggesting that prolonged periods of activation are not necessary to sustain even the slow fiber phenotype Hensbergen and Kernell, 1997;Pierotti et al, 1991).…”

mentioning

confidence: 99%

Does daily activity level determine muscle phenotype?

Hodgson

Roy

Higuchi

et al. 2005

Journal of Experimental Biology

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“…These findings also imply that muscles innervated from the epicenter are likely to be reinnervated, not normally innervated. While inactivity can reduce muscle fiber areas up to 50%, 33 motoneuron death and muscle denervation must contribute to the severe atrophy that is measured in muscles after spinal cord injury (e.g. 70% on average in triceps brachii and vastus lateralis).…”

Section: Motoneuron Death Occurs Irrespective Of the Level Or Cause Omentioning

confidence: 99%

Motoneuron Death after Human Spinal Cord Injury

Grumbles

Thomas

2017

Journal of Neurotrauma

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The severe muscle weakness and atrophy measured after human spinal cord injury (SCI) may relate to chronic muscle denervation due to motoneuron death and/or altered muscle use. The aim of this study was to estimate motoneuron death after traumatic human SCI. The diameter and number of myelinated axons were measured in ventral roots post-mortem because ventral roots contain large diameter (> 7 lm) myelinated axons that typically arise from motoneurons and innervate skeletal muscle. In four cases (SCI levels C7, C8, T4, and L1) involving contusion (n = 3) or laceration (n = 1), there was a significant reduction in the number of large diameter myelinated axons at the lesion epicenter (mean -standard error [SE]: 45 -11% Uninjured), one level above (51 -14%), and one (27 -12%), two (45 -40%), and three (54 -23%) levels below the epicenter. Reductions in motoneuron numbers varied by side and case. These deficits result from motoneuron death because the gray matter was destroyed at and near the lesion epicenter. Muscle denervation must ensue. In seven cases, ventral roots at or below the epicenter had large diameter myelinated axons with unusually thin myelin, a sign of incomplete remyelination. The mean -SE g ratio (axon diameter/fiber diameter) was 0.60 -0.01 for axons of all diameters in five above-lesion ventral roots, but increased significantly for large diameter fibers ( ‡ 12 lm) in three roots at the lesion epicenter. Motoneuron death after human SCI will coarsen muscle force gradation and control, while extensive muscle denervation will stifle activity-based treatments.

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“…The spinal cord was completely transected at the junctions of T12-T13 and again at L7-S1. These procedures result in near inactivity of the hindlimb muscles for prolonged periods in cats (Eldridge et al, 1981;Pierotti et al, 1991) and rats (Roy et al, 2007). The procedures for the postsurgical care of spinal-injured cats are detailed in Roy et al .…”

Section: Materials and Methods Surgical And Motor Unit Isolation Procmentioning

confidence: 99%

“…The lumbar region of the spinal cord of nine adult female cats (body weight, 2.3-3.8·kg) was isolated surgically as described by Pierotti et al (Pierotti et al, 1991). Under deep pentobarbital anesthesia (35·mg·kg -1 ) and aseptic conditions, a partial laminectomy was performed from T12 to S2 and a bilateral dorsal rhizotomy was performed intradurally between T12 and S2.…”

Section: Materials and Methods Surgical And Motor Unit Isolation Procmentioning

confidence: 99%

Persistence of motor unit and muscle fiber types in the presence of inactivity

Roy

Pierotti

Garfinkel

et al. 2008

Journal of Experimental Biology

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SUMMARYThe clarity of categorizing skeletal muscle fibers in individual motor units into phenotypes based on quantitative single fiber enzyme activities and as a function of neuromuscular activity level was examined. Neuromuscular activity was eliminated in adult cat hindlimb muscles by spinal cord isolation (SI), i.e. complete spinal cord transection at a low thoracic and a high sacral level with bilateral dorsal rhizotomy between the transection sites. One motor unit was isolated via ventral root teasing procedures from the tibialis anterior (TA) muscle of each hindlimb in control and SI cats, and physiologically tested and glycogen depleted through repetitive stimulation; fibers comprising each motor unit were visualized through glycogen staining. Each motor unit was composed of fibers of the same myosin immunohistochemical type. Myofibrillar adenosine triphosphatase, succinate dehydrogenase and ␣-glycerophosphate dehydrogenase activities were determined for a sample of motor unit and non-motor unit fibers, providing a measure of three enzyme activities often used to characterize fiber phenotype within a single unit. Although normal enzyme activities were altered after 6·months of inactivity, the relationships among the three enzymes were largely maintained. These data demonstrate that it is not the diversity in any single enzyme property but the profile of several metabolic pathways that underlies the significance of fiber phenotypes. These profiles must reflect a high level of coordination of expression of selected combinations of genes. Although neuromuscular activity level influences fiber phenotype, the present results demonstrate that activity-independent mechanisms remain important sources of the control of phenotype establishment in the near absence of activity.

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Mechanical and morphological properties of chronically inactive cat tibialis anterior motor units.

Cited by 76 publications

References 38 publications

Does daily activity level determine muscle phenotype?

Does daily activity level determine muscle phenotype?

Motoneuron Death after Human Spinal Cord Injury

Persistence of motor unit and muscle fiber types in the presence of inactivity

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