A hierarchy of determining factors controls motoneuron innervation

Quail leg buds were grafted in place of chick leg buds or chick wing buds and vice versa at stages 18 to 21 after colonization by muscle precursor cells had been completed. Motor endplate pattern in the plantaris muscle of the grafts was analyzed before hatching by means of esterase and acetylcholinesterase staining techniques. Muscle fibre types were made visual using the myosin ATPase reaction. Investigations are based on the species-specific endplate pattern of the plantaris muscle: multiply innervated fibres in the chick and focally innervated fibres in the quail. Muscle pieces isolated from the adjacent medial gastrocnemius muscle of the grafted legs were histologically examined to judge their species-specific composition. Horseradish peroxidase was injected into the plantaris muscles of both the grafted and the opposite leg as well as in the plantaris muscle of normal quail embryos, in order to be sure that the plantaris muscle of the graft is innervated by appropriate motoneurons. This procedural design offers for the first time a possibility to test experimentally the influences of motoneurons on endplate pattern formation under conditions corresponding to those in normal ontogenesis. It is shown that such appropriate motoneurons of one species which project to the plantaris muscle of the other species dictate the endplate pattern. When the plantaris muscle is innervated by inappropriate motoneurons, the endplate pattern inherent in the muscle primordium itself becomes realized. A sequence of hierarchically acting factors is proposed to bring different results in line. According to this, the neuronally set programme has priority compared with that set in the muscle. This is true for the normal development and might generate the high neuro-muscular specificity. If under experimental conditions the neuronal programme and the peripheral programme differ, the axons and muscle fibres selectively interact with respect to their inherent characteristics and the muscle-specific programme becomes expressed. If there is a lack of a certain axon type, muscle fibres might become innervated by non-corresponding motoneurons which alter the muscle fibre type.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47522/1/429_2004_Article_BF00309770.pd

Morphologic Differences in Skeletal Muscle with Age in Normally Active Human Males and Their Well-Trained Counterparts

In this study we elucidate the interaction of physical activity with aging as regards skeletal muscle fiber distribution and size. Thirty-three male athletes and 42 normally active counterparts served as subjects. They were assigned to younger (\u3c25.5 years) and older (\u3e25.5 years) subgroups. Serial cross-sections from muscle biopsy samples (musculus vastus lateralis) were stained to distinguish fiber type: fast glycolytic (type IIb), fast oxidative-glycolytic (type Ha), or slow oxidative (type I). We also measured fiber diameters. A greater mean diameter of type I fibers was seen in older as opposed to younger athletes. Older controls had a smaller mean diameter of type IIb fibers than did younger controls. Athletes had a smaller mean percentage of type Ha fibers and a greater mean percentage of type I fibers than did controls. There was a greater mean percentage of type I fibers in older as opposed to younger controls, but this was not the case in athletes. Athletes may have larger fibers and a greater percentage of type I fibers at the expense of type Ha fibers. Atrophy of fibers with aging might be retarded by training, which might also reduce the age-associated rate of type IIb percentage loss and type I percentage gain

Is muscle power output a key factor in the age-related decline in physical performance? A comparison of muscle cross section, chair-rising test and jumping power

Ageing compromises locomotor capacity and is associated with an increased risk of falls. Several lines of evidence indicate that both changes in muscle mass and performance are causative. Most studies, however, do not discern between effects of ageing, sedentarism and comorbidity. The present study compares the age effects in muscle cross section, force and power in physically competent self-selected subjects of different age groups. A total of 169 women and 89 men between 18 and 88 years, without any disease, impairment or medication affecting the musculoskeletal system were enrolled in this study. Calf muscle cross-sectional area was assessed by computed tomography. Muscle force and power were assessed by jumping mechanography. No significant correlation between muscle cross section and age was found in the men. A weak correlation in the women disappeared after correction for height. Close correlations with age, however, were found for peak force and peak power. Correction for muscle cross section or body weight further increased these correlation coefficients, particularly for peak power specific to body weight (r = 0.81 in women and r = 0.86 in men). The non-sedentarian population investigated here depicted a reduction of >50% between the age of 20 and 80 without a reduction in muscle cross section. This suggests a crucial role for muscular power in the ageing process. Possibly, the jumping mechanography as a measurement of anti-gravitational power output is a promising extension of the chair-rising test, known to be predictive for immobilization and the risk of falls

Efeito da natação associado a diferentes dietas sobre o músculo tibial anterior do rato: estudo morfológico e histoquímico Efecto de la natación asociado a diferentes dietas sobre el músculo tibial anterior del ratón: estudio morfológico e histo-químico Effect of swimming associated with diet on the anterior tibial muscle of rats: morphological and hystochemical study

O objetivo deste estudo foi investigar o efeito da associação de diferentes freqüências de programas de natação e dietas nas características do músculo tibial anterior. Foram utilizados 24 ratos machos Wistar. Estes foram aleatoriamente divididos em três grupos: não treinados (controle), grupo treinado (2x/sem) e grupo treinado (5x/sem). Cada grupo foi dividido em dois grupos, os quais receberam uma das dietas: normal ou hipercalórica. Depois do período de treinamento, amostras do músculo foram coletadas e congeladas a -70ºC. Cortes histológicos (8µm) obtidos em um micrótomo criostato (-20º) foram submetidos aos métodos HE e NADH-TR, m-ATPase (pH 4,4) e Sudan Black. A morfologia e o grau de hipertrofia foram avaliados usando o método do menor diâmetro. Os dados foram submetidos ao teste de variância (ANOVA-one way). As fibras musculares foram classificadas como SO, FOG e FG, apresentando um padrão de distribuição em mosaico em todos os grupos. As fibras musculares revelaram leve hipertrofia em todos os grupos. Os pesos inicial e final foram significativamente diferentes nos grupos treinados. Nos grupos treinados, especialmente no grupo de 5x/sem, as fibras musculares revelaram hipertrofia e splitting com alguns mionúcleos internos. Algumas fibras revelaram-se atrofiadas e esta observação sugeriu desnervação. O metabolismo oxidativo foi mais intenso nas fibras SO e FOG; não houve alterações na habilidade contrátil do músculo e o teor de lipídios foi intenso nas fibras SO, moderado nas FOG e fraco nas FG. O presente estudo, com este protocolo, treinamento de 2x/sem e 5x/sem, causou diferentes tipos de lesões morfológicas nas fibras. A dieta hipercalórica não causou resultados estatisticamente significantes em comparação com a dieta normal.<br>El objetivo de ese estudio fue investigar el efecto de la asociación de frecuencias diferentes de programas de natación y dietas en las características del músculo tibial anterior. Se usaron 24 ratones masculinos Wistar. Éstos fueron aleatoriamente divididos en 3 grupos: no especializado (control), el grupo especializado (2 x/sem) y el grupo 2 especializado (5 x/sem). Cada grupo era dividido en 2 grupos que recibieron uno de las dietas: normal o hipercalórica. Después del periodo de entrenamiento las muestras del músculo fueron recogidas y reunido congeladas a -70ºC. Los cortes histológicos (8µm) obtenidos con un micrótomo de criostato (-20º) los mismos fueron sometidos a los métodos HE y NADH-TR, m-ATPase (pH 4,4) y Negro de Sudán. Se estimaron la morfología y el grado de la hipertrofia usando el método del diámetro más pequeño. Los datos se sometieron a prueba variable (ANOVA-one way). Las fibras musculares fueron clasificadas como SÓ, FOG y FG, presentando una distribución "de modelo en mosaico" en todos los grupos. Las fibras musculares revelaron una hipertrofia ligera en todos los grupos. Los pesos inicial y final fueron significativamente diferentes en los grupos especializados. Sobre todo en el grupo de 5 x/sem, de los grupos especializados, las fibras musculares revelaron hipertrofia, splitting, e con algunos mionúcleos internos. Algunas fibras se revelaron atróficas, y esta observación hizo pensar en una denervación. La oxidación del metabolismo SÓ era más intensa en las fibras y en el FOG; no había alteraciones en la habilidad contráctil del músculo y el tenor de lípidos en el grupo SÓ era intenso en las fibras, moderado en el FOG y débil en FG. El estudio presente, con este protocolo, en los grupos entrenados de 2 x/sem y 5 x/sem, causó tipos diferentes de lesiones morfológicas en las fibras. Los de dieta hipercalórica no provocaron resultados estadísticamente significativos comparados con los de la dieta normal.<br>The objective of this study was to investigate the effect of the association of different swimming program frequencies and diets on the characteristics of the anterior tibial muscle of 24 Wistar male rats. These rats were randomly assigned into three groups: untrained (control), trained group (two days/week) and trained group (five days/week). Each group was divided into two groups, which received one of the two normal or high calorie diets. After the training period, muscle samples were collected and frozen at -70ºC. Serial cryostat sections (8 mum) were sectioned and submitted to HE stain and to NADH-TR, m-ATPase (pH 4.4) and Sudan Black histochemical methods. The morphology was analyzed and the degree of fiber enlargement (on hypertrophy) evaluated using the lesser fiber diameter method. The data were submitted to analysis of variance (one way ANOVA). Muscle fibers were classified as SO, FOG and FG, presenting a mosaic distribution pattern, which were unchanged in all groups. Muscle fibers revealed a very low hypertrophy in all groups. Initial and final body weight were significantly different in trained groups. In the trained groups, especially in five days/week, muscle fibers revealed higher diameter, splitting and some internal myonucleus. Some atrophic fibers were observed and this observation was suggestive of denervation. The oxidative metabolism was higher in SO and FOG fibers. No significant alterations were observed in muscle contraction ability and the lipids content was intense in SO fibers, moderate in FOG fibers and low in FG fibers. The present study, with this protocol of two days/week and five days/week training caused different types of morphological lesions in fibers. The high calorie diet did not cause statistically significant results in comparison with the normal diet

Variability in fibre properties in paralysed human muscles and effects of training

Item does not contain fulltextA spinal cord injury usually leads to an increase in contractile speed and fatigability of the paralysed quadriceps muscles, which is probably due to an increased expression of fast myosin heavy chain (MHC) isoforms and reduced oxidative capacity. Sometimes, however, fatigue resistance is maintained in these muscles and also contractile speed is slower than expected. To obtain a better understanding of the diversity of these quadriceps muscles and to determine the effects of training on characteristics of paralysed muscles, fibre characteristics and whole muscle function were assessed in six subjects with spinal cord lesions before and after a 12-week period of daily low-frequency electrical stimulation. Relatively high levels of MHC type I were found in three subjects and this corresponded with a high degree of fusion in 10-Hz force responses (r=0.88). Fatigability was related to the activity of succinate dehydrogenase (SDH) (r=0.79). Furthermore, some differentiation between fibre types in terms of metabolic properties were present, with type I fibres expressing the highest levels of SDH and lowest levels of alpha-glycerophosphate dehydrogenase. After training, SDH activity increased by 76+/-26% but fibre diameter and MHC expression remained unchanged. The results indicate that expression of contractile proteins and metabolic properties seem to underlie the relatively normal functional muscle characteristics observed in some paralysed muscles. Furthermore, training-induced changes in fatigue resistance seem to arise, in part, from an improved oxidative capacity