Motor Unit in Old Age

Gutmann, E; Hanzlíková, V.

doi:10.1038/209921b0

Cited by 145 publications

(50 citation statements)

References 3 publications

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“…Wray (1969), who determined the number of motor units in the much larger baboon, encountered similar difficulties and often was forced to use de-efferentiation rather than deafferentiation. Nevertheless, Zelena and Hnik (1963), Gutmann andHanzlikova (19661, andCharron (1982, 1983) determined in rats the number of motor axons in deafferentiated nerves of the soleus and anterior tibial muscles, and in the deafferentiated sural nerve. Zelena and Hnik (1963) and Charron (1982, 1983) do not report technical difficulties.…”

Section: Discussionmentioning

confidence: 97%

Fiber composition of the rat sciatic nerve

1986

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The rat sciatic nerve originates from the spinal segments L4-L6. It is unifascicular at the trochanter; 5-7 mm distally, the nerve splits into two and then into four fascicles. The tibial portion gives rise to the tibial and the sural nerves, and the peroneal portion gives rise to the peroneal nerve and a cutaneous branch that perforates the lateral hamstring muscles to innervate the proximolateral face of the calf. The number and type of the axons in these branches were determined in light and electron micrographs of normal nerves, and after de-efferentation or sympathectomy. Deafferentation was technically not feasible because spinal ganglia and ventral roots were supplied by the same vascular plexus. The tibial nerve contained 1,000 motor and 3,500 myelinated afferent axons, 3,700 sympathetic axons, and 5,400 unmyelinated afferent axons. The peroneal nerve contained 600 motor and 1,300 myelinated afferent axons, 1,100 sympathetic axons and 3,000 unmyelinated afferent axons. The sural nerve contained 1,100 myelinated and 2,800 unmyelinated afferent axons; in addition, there were 1,500 unmyelinated sympathetic axons. The cutaneous branch consisted of 400 myelinated and 1,800 unmyelinated afferent axons. Thus, the entire sciatic nerve at midthigh is composed of about 27,000 axons; 6% are myelinated motor axons, 23% and 48% are myelinated and unmyelinated sensory axons, respectively, and 23% are unmyelinated sympathetic axons. The techniques used did not demonstrate sympathetic axons in the cutaneous branch and did not reveal the few motor axons contained in the sural nerve.

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Section: Discussionmentioning

confidence: 97%

Fiber composition of the rat sciatic nerve

1986

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“…Even more evident is the fact that, in the biopsies harvested from senior sportsmen, the slow type fibers are grouped in larger areas (mean 8.4 %, see Table 2), almost reaching the 92% in the extreme cases (Table 3). It has long been recognized that the histological changes seen in aging muscle suggest that denervation significantly contributes to muscle decay [8,25,28] and that immobility accelerates the deterioration process [6], while running activity sustained for decades (as that performed by master athletes) protects against the age-related loss of motor units [16,19,20] and, thereby, protects lean muscle mass [32]. However, the degree to which denervation causes muscle fiber transformation and loss of myofibers is an open issue in humans, since reinnervation events may compensate long-term for motor neuron loss in spinal cord and/or axonal abnormalities in peripheral nerves [1,7,14,15].…”

Section: Resultsmentioning

confidence: 99%

Reinnervation of Vastus lateralis is increased significantly in seniors (70-years old) with a lifelong history of high-level exercise

Mosole¹,

Rossini²,

Kern

et al. 2013

Eur J Transl Myol

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It has long been recognized that histological changes observed in aging muscle suggest that denervation contributes to muscle deterioration and that disuse accelerates the process while running activity, sustained for decades, protects against age-related loss of motor units. Here we show at the histological level that lifelong increased physical activity promotes reinnervation of muscle fibers. In muscle biopsies from 70-year old men with a lifelong history of high-level physical activity, we observed a considerable increase in fiber-type groupings (almost exclusively of the slow type) in comparison to sedentary seniors, revealing a large population of reinnervated muscle fibers in the sportsmen. Slow-type transformation by reinnervation in senior sportsmen seems to be a clinically relevant mechanism: the muscle biopsies fluctuate from those with scarce fiber-type transformation and groupings to almost fully transformed muscle, going through a process in which isolated fibers co-expressing fast and slow MHCs seems to fill the gaps. Taken together, our results suggest that, beyond the direct effects of aging on the muscle fibers, changes occurring in skeletal muscle tissue appear to be largely, although not solely, a result of sparse denervation. Our data suggest that lifelong exercise allows the body to adapt to the consequences of the age-related denervation and to preserve muscle structure and function by saving otherwise lost muscle fibers through recruitment to different, mainly slow, motor units. These beneficial effects on motoneurons and, subsequently on muscle fibers, serve to maintain size, structure and function of muscle fibers, delaying the functional decline and loss of independence that are commonly seen in late aging. Trial Registration: ClinicalTrials.gov: NCT01679977

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“…Both a slow loss of neuromuscular contact due to degeneration at the end-plate region and a loss of entire motoneurones have been suggested. Gutmann & Hanzlikova (1966) concluded that the age-related fibre loss in rat soleus muscle, between adult (4 months) and old (24 months) animals, was secondary to a degeneration of motor end-plates, which was found to cause a 33 % decrease in motor unit innervation ratio but no change in the number of motor units. This conclusion was based on measurements of the number of myelinated nerve fibres in the motor nerve to soleus and the total number of muscle fibres in soleus together with morphological studies of end-plate structures.…”

Section: Discussionmentioning

confidence: 99%

Effects of age on contractile and enzyme‐histochemical properties of fast‐ and slow‐twitch single motor units in the rat.

Edström

Larsson

1987

The Journal of Physiology

137

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SUMMARY1. Contractile, enzyme-histochemical and morphometrical properties of muscle fibres were studied in single motor units of tibialis anterior (t.a.) and soleus muscles in young (3-6 months) and old (20-24 months) male albino rats. The technique of measuring glycogen depletion as a marker of previous muscle contraction was used for direct correlation of enzyme-histochemical and contractile parameters within single motor units of the fast-and slow-twitch type.2. In t.a., the fast-twitch motor units covered 18 + 9 and 22 + 16 % (P = not significant, n.s.) of t.a. cross-sections, included 148 + 65 and 162 + 63 muscle fibres per unit (P = n.s.) and had a cross-sectional area of 0-50+0-32 and 0-44+0-22 mm2 (P = n.s.) in the young and old animals, respectively (means+ S.D.).3. In soleus, the slow-twitch motor units covered 53 + 11 and 71 + 12 % (P = n.s.), included 55 + 10 and 83 + 13 muscle fibres per unit (P < 0-01) and had a total crosssectional area of 0 14 + 0-02 and 0-22 + 0-06 mm2 (P < 0-01) in the young and the old animals, respectively. The calculated number of motor units in soleus accordingly decreased (P < 0'01) from 49+ 10 in the young to 29+ 10 in the old animals resulting in a loss of muscle fibres and an increased innervation ratio in old age (mean + S.D.).4. Clusters of more than three muscle fibres were rarely seen in any of the glycogendepleted motor units in either the young or the old animals. However, in the slowtwitch motor units of old animals the muscle fibres were less randomly distributed within the motor unit territory (P < 0 05), indicating a denervation-reinnervation process.5. The contraction and half-relaxation times of the isometric twitch were significantly prolonged in old age. In 274 randomly isolated single motor units of t.a. the contraction time increased from 13 +1 in young animals to 17 + 3 ms in old ones and the half-relaxation time from 12 + 2 to 16 + 5 ms (P < 0-01 in both cases). In 236 randomly isolated soleus single motor units, the contraction and half-relaxation times increased (P < 0-001) from 24 + 5 to 31 + 7 ms and from 26 + 8 to 35 + 9 ms, respectively (means+ S.D.).Authors' names are in alphabetical order. * To whom reprint requests should be addressed. L. EDSTROM AND L. LARSSON 6. The results show that the age-related decrease in the number of muscle fibres is due to a loss of whole motor units and that in old age reinnervation of previously denervated muscle fibres is incomplete.7. It is concluded that the reduced speed of isometric contraction during ageing is primarily related to changes in the contractile properties of both fast-and slowtwitch motor units, and that the age-related decrease in the number of type II muscle fibres observed in soleus is of less importance in this respect.

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Motor Unit in Old Age

Cited by 145 publications

References 3 publications

Fiber composition of the rat sciatic nerve

Fiber composition of the rat sciatic nerve

Reinnervation of Vastus lateralis is increased significantly in seniors (70-years old) with a lifelong history of high-level exercise

Effects of age on contractile and enzyme‐histochemical properties of fast‐ and slow‐twitch single motor units in the rat.

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