Changes In Fiber Diameter Research Articles

Physiological and histochemical changes of the extensor digitorum longus and soleus muscles after lateral cordotomy in the albino rat

The physiological and histochemical effects of unilateral and bilateral cordotomy on the extensor digitorum longus and soleus muscles were studied in the albino rat. After unilateral cordotomy, the ipsilateral extensor digitorum longus and soleus muscles became slower and relatively faster, respectively, compared to the contralateral and normal muscles. No gross histological abnormalities were found, but changes in fiber diameter and typology were statistically significant in both muscle types compared to their contralateral muscles, and were in substantial agreement with the changes observed on the contractile force and kinetics of the isometric twitch. Bilateral cordotomy in adult animals, like unilateral cordotomy in immature animals, affected only the soleus muscle fiber types. The results have implications for the role of the upper motoneuron physiological and histochemical trophic influences in controlling slow and fast motor units.

Denervation and reinnervation of fast and slow muscles. A histochemical study in rats.

A histochemical study, using myosin-adenosine triphosphatase activity at pH 9.4, was conducted in soleus and plantaris muscles of adult rats, after bilateral crushing of the sciatic nerve at the sciatic notch. The changes in fiber diameter and per cent composition of type I and type II fibers plus muscle weights were evaluated along the course of denervation-reinnervation curve at 1, 2, 3, 4 and 6 weeks postnerve crush. The study revealed that in the early denervation phase (up to 2 weeks postcrush) both the slow and fast muscles, soleus and plantaris, resepctively, atrophied similarly in muscle mass. Soleus increased in the number of type II fibers, which may be attributed to "disuse" effect. During the same period, the type I fibers of soleus atrophied as much or slightly more than the type II fibers; whereas the type II fibers of plantaris atrophied significantly more than the type I fibers, reflecting that the process of denervation, in its early stages, may affect the two fiber types differentially in the slow and fast muscles. It was deduced that the type I fibers of plantaris may be essentially different in the slow (soleus) and fast (plantaris) muscles under study. The onset of reinnervation, as determined by the increase in muscle weight and fiber diameter of the major fiber type, occurred in soleus and plantaris at 2 and 3 weeks postcrush, respectively, which confirms the earlier hypotheses that the slow muscles are reinnervated sooner than the fast muscles. It is suggested that the reinnervation of muscle after crush injury may be specific to the muscle type or its predominant fiber type.

Selection for clean fleece weight in Merino sheep. II.* Correlated responses to selection

Correlated responses to selection for high and low clean fleece weight (W) in the Peppin Merino (Fleece plus and Fleece minus flocks respectively) are presented together with estimates of realized genetic correlations where appropriate. There were strong positive correlations between W and greasy fleece weight and between W and clean scoured yield, and a strong negative correlation between Wand crimp frequency. There was no consistent association between W and body weight. Selection for W caused little change in wool colour, a slight improvement in wool character, and an improvement in wool handle in the rams, but not in the ewes. There was an increase in face cover score and a decrease in birthcoat score in the Fleece minus flock, but there was no change in either trait in the Fleece plus flock. Possible reasons for these asymmetries are discussed. Most of the response in W in the Fleece plus flock arose through increases in fibre density, fibre diameter and staple length. Staple length was the major component associated with response in W in the Fleece minus flock. Decreases also occurred in fibre density and wrinkle score but there was no change in fibre diameter. Continued response in W in the Fleece minus flock was through staple length and, to a lesser extent, wrinkle score. The response in fibre density in both flocks arose through change in the ratio of secondary to primary fibres. Two-year-old and lifetime reproductive performances are reported for the two selection flocks. The Fleece minus 2-year-old ewes weaned significantly more lambs than their Fleece plus counterparts over the period studied. The lifetime reproductive performance of ewes was similar in both flocks, although there were significantly more multiple births in the Fleece plus flock. An examination of the divergence between the two flocks revealed no significant time trends. The asymmetrical pattern of response in W in these flocks is discussed in the light of the present data. __________________ *Part I, Aust. J. Agric. Res., 25: 643 (1974).

Morphological and physiological measures of trophic dependence in a crustacean muscle

Tenotomy of crayfish opener muscles, or severing of the opener motor innervation while motor terminals may remain intact (decentralization), produces no change in fiber resting potential or input resistance within 75 to 245 days. Immobilization or “decentralization” of the same muscle mass produces no significant change in fiber diameter within 237 or 172 days, respectively, although some atrophy was noted after “denervation” for 267 days, at which time most severed nerve terminals have probably degenerated. Tenotomization produces a 15–35% shortening of the muscle resting length and leads to a significant decrease in fiber diameter within 15 days. Progressive atrophy following tenotomy is associated with a progressive decrease in fiber resting length. These results suggest that fiber diameter is heavily dependent upon the maintenance of a minimum resting length rather than upon muscle fiber activity (“use”) or upon a neurotrophic substance. Conversely, the maintenance of membrane resting potential and input resistance do not necessarily depend upon neurotrophic substances, muscle activity, or muscle resting length.

Trophic dependence of fiber diameter in a crustacean muscle

Denervation or immobilization of crayfish opener muscles produces little or no atrophic change in fiber diameter within 250 days whereas tenotomy of the same muscle leads to significant fiber atrophy within 50 days. The observations that opener nerve terminals probably degenerated 40–90 days prior to sampling denervated muscles, and that opener muscle fibers are 10–30% shorter in tenotomized muscles than for muscles immobilized in the fully open position, lead to the conclusion that opener fiber diameter is much more dependent on muscle length (or passive tension) than upon neurotrophic factors or muscle activity. These results differ from those reported for most vertebrate twitch muscles which undergo significant atrophy after denervation, immobilization, or tenotomy. These data from a polyneuronal, multiterminal, tonic muscle of a crayfish closely resemble results obtained from avian muscles having similar innervation patterns and suggest that one or more of their common functional properties may determine their similar trophic dependencies.

The effect of fibre diameter on the dynamic properties of glass-fibre-reinforced polyester resin

The effect of fibre diameter on the mechanical properties of unidirectional composites was investigated using a glass/polyester system. The specimens were vibrated in flexure and longitudinal shear, and finally tested to destruction in interlaminar shear.To allow for changes in fibre diameter at constant fibre volume fraction, the surface area of fibre per unit volume, Af, was defined.It was found that the fibre diameter had no significant effect on Young's modulus in flexure, nor on the longitudinal shear modulus and damping. However, there was a pronounced variation of flexural damping with fibre diameter and fibre volume fraction, and hence with Af. The interlaminar shear strength was low for small values of Af, but rapidly tended to an average of about 56 MN m−2.

Effects of divergent selection for body weight on fibre number and diameter in two mouse muscles

SUMMARYThe effects of selection for increased or decreased body weight in mice, at 5 or 10 weeks of age, on the fibre number, fibre diameter and weight of the m. sternomastoideus and m. anterior tibialis muscles were studied. Unselected control mice were also included. Significant effects were detected in the case of each of the traits. However, the magnitude of any particular correlated response to selection varied between muscles and between selection ages in an unsystematic fashion. Most of the changes in muscle weight resulting from selection were attributable to positively correlated changes in fibre number but they were also accompanied by changes in fibre diameter in some cases.The correlated responses described indicate the difficulty of predicting how selection for body weight changes will influence cellular structure of any given muscle.Phenotypic correlations between muscle fibre number and diameter were essentially zero. The phenotypic correlations between muscle weight and fibre number and fibre diameter were positive.Sex had no effect on fibre number but had an effect on fibre diameter which depended on the particular muscle and the age of the animal.

Drought feeding of sheep. 3. The relative importance of components of wool growth in explaining the wool growth differences between strains and diets

This paper reports the changes in wool components with differences in wool growth resulting from differences in strain of sheep and diet, and the importance of these in relation to selecting a strain of Merino for the drier pastoral areas. Measurements of body weight, fold score, staple length, fibre diameter and follicle density were taken from Collinsville, Peppin and Bungaree ewes grazing natural pasture at Trangie and also when given a maintenance ration containing different grains, different protein supplements and formaldehyde treatment of these protein supplements. At pasture the Collinsville strain produced more wool with little increase in fibre diameter, when compared with the Peppins, and this resulted in the Collinsville strain being more profitable under pasture conditions than either the Peppins or Bungarees. When given a survival ration, similar changes in wool growth and the components occurred in each strain helping to maintain the profitable advantage of the Collinsvilles. The effect of the dietary treatments on wool growth occurred mainly through changes in fibre diameter and length. It is concluded that the choice of a particular strain of sheep for use in drier areas should not be influenced by the nutritional environment under which they are chosen.

Cycles of wool follicle activity in some shetland sheep

SUMMARYThe wool growth cycle in three rams and three ewes was studied by taking monthly wool and skin samples for periods up to 3 years. The percentage of inactive follicles and of medullated fibres was recorded, fleece length was measured and change in fibre diameter and pigmentation between summer and winter was investigated.Casting of the fleece appeared to depend more on the thinning of fibres than on the proportion with brush ends, casting in some instances taking place with only 30% brush ends, while not in others with as much as 70% follicle inactivity.Follicles began to become inactive in both sexes in September following the autumnal equinox. The secondary follicles had a greater proportion of inactivity (mean of 45% compared with 20% in the primaries) but tended to regrow earlier, and regrowth in the rams tended to begin before that in the ewes. Regrowth as a whole began from January to March. Subsidiary cycles of inactivity of about 2 months' duration were evident.Maximum growth in length occurred between April and October. A difference in mean diameter of only a few microns could be detected between summer and winter. Maximum medullation occurred in July in the rams and August in the ewes. Decrease in pigmentation in winter was brought about by a lowering of the density of pigment granules within the fibres.

The effect of substrate on Reinforced Pyrolytic Graphite

Reinforced Pyrolytic Graphite, RPG † † Registered trademark for Reinforced Pyrolytic Graphite, fabricated by the Super-Temp Company, a Division of Ducommun, Incorporated, 11120 South Norwalk Boulevard, Santa Fe Springs, California 90670. , was prepared from various substrates including rayon, nylon, wool, cotton, and polyurethane foam. In all cases, the ultimate flexure or compressive strength increases with the final bulk density of the RPG. Most of the experiments were done with rayon where it was found that for a given final density, the strength increased as the fiber length or the initial rayon density decreased, but that the strength was not noticeably affected by changes in fiber diameter or carbonization process. RPG produced from wool gave the highest flexural strength for a given density. The carbons resulting from nylon and cotton were, in general, mechanically inferior to carbons from wool or rayon. The carbon from polyurethane foam was not infiltrated and thus had very low final densities and compressive strengths, and these were independent of pore size in the foam. However, this material is primarily for use as a thermal insulator and direct comparisons of strength with rayon and wool carbons were not intended.

The effect of exercise on skeletal muscle fibres

1. 1. The duration of the exercise was found to be important in producing fibre hypertrophy than the intensity. 2. 2. Long duration exercise caused significant fibre hypertrophy whereas short duration exercise caused significant hypotrophy. 3. 3. These changes in fibre diameter were accomplished after 19 days. 4. 4. Swimming exercises caused no significant changes in fibre diameter. 5. 5. The increment in oxygen consumption was used as an indication of the the work done during exercise.

The effect of thyroxine implantation on wool growth

1. An experiment was carried out to determine the effect of L-thyroxine implantation upon the wool production and live-weight change of Corriedale and Suffolk × Border Leicester-Merino sheep.2. Groups fed hay in restricted amounts gave approximately 12% more wool when treated with thyroxine. Since there was no change in fibre diameter, this was presumably due to an increase in staple length.3. Groups fed hay ad lib. gave no significant increase in wool production when treated with thyroxine, nor did their rate of food consumption alter. Their level of wool production over the 5-month period was approximately the same as that of the thyroxine treated, restricted fed, sheep.4. All thyroxine-treated groups lost approximately 10% of their live weight. This was in the nature of a steady decrease from the second to the seventh week after treatment. Live weights then remained at about the same level for a further 8–10 weeks when they commenced to return gradually to their original weights.