Alfred Maier

Properties of immobilized hind-limb muscles of the Galago senegalensis.

Abstract Morphological, biochemical, and physiological properties of longterm (6 mo) immobilized skeletal muscles of a nonhuman primate were studied in seven Galago senegalensis which were immobilized at the ankle and knee of one hind limb with an external brace. Electromyographic activity of the ipsilateral and contralateral quadriceps and muscles of the calf were assessed after 5 and 6 mo of immobilization. The EMG was markedly reduced in the immobilized muscles compared to the contralateral control when the brace was intact and the animal moving freely. Without exception, extensor muscles atrophied more than flexors. The soleus, a slow-twitch muscle atrophied more than any other muscle of the lower leg but the same was not true of the vastus intermedius the analogous muscle of the thigh. Slow-twitch oxidative fibers (SO) were atrophied more than fast-twitch oxidative glycolytic fibers (FOG), and FOG tended to atrophy more than fast-twitch glycolytic fibers (FG). The immobilized soleus and vastus intermedius had a smaller percentage of SO fibers than their controls, suggesting that they had faster contraction times. With respect to alterations in reduced nicotinamide adenine dinucleotide diaphorase activity, no consistent pattern was observed except for a greater coarseness of staining granules and more homogeneous dispersion of the granules throughout the cross-section of the fibers. No changes were found in phosphorylase, lactate dehydrogenase, or succinate dehydrogenase specific activity or in myoglobin concentration in homogenates of ankle flexors or the vastus lateralis. Myosin ATPase, but not actomyosin ATPase activity was significantly less in the immobilized gastrocnemius-plantaris muscles. No change in contractile properties related to speed were observed in the plantaris. This muscle did exert more twitch and tetanic tension per gram of muscle in the immobilized leg.

The effects on spindles of muscle atrophy and hypertrophy

Abstract The effects of decreased and increased use on the morphology, histochemistry and discharge of spindles in the cats medial gastrocnemius muscle were studied in chronic preparations in which one leg either had been immobilized in a cast or the synergist muscles had been denervated. Comparisons were also made of histochemically typed populations of extrafusal fibers in the experimental and the contralateral muscles. The cross-sectional areas of both nuclear bag and chain IF fibers were found to be reduced in the immobilized muscles and increased in the synergists-denervated series relative to the areas in contralateral muscles. Proportionately, however, the changes in IF fibers were less than those found among extrafusal fibers. In the immobilized series the bilateral difference in bag fiber areas was greater than that of the chain fibers, while among extrafusal fibers slow-twitch fibers were affected more than fast-twitch fibers. The discharge of spindle units monitored from dorsal root filaments at resting muscle length was elevated in the immobilized muscles, as was also the stretch sensitivity, i.e., increase in pulse rate per increment of gross muscle stretch. In muscles of the synergists-denervated series the background discharge was increased also, but the effect on stretch sensitivity was not clearly defined.

Differences in intrafusal fiber content of spindles in several muscles of the cat

Abstract The intrafusal fiber content observed in 850 spindles from seven kinds of limb muscles of the cat are presented. The tenuissimus had the smallest content, 6.14 fibers per spindle, and the extensor digitorum longus the largest, 7.91. Gastrocnemius spindles had more fibers than those in the soleus. The differences were attributable primarily to variation in number of nuclear chain fibers. No infallible correlation with anatomical or functional characteristics of the muscles was evident, although greater fiber content seemed to be associated with flexor action and fast contractility. The possible consequences of the spindle content of intrafusal fibers on static and dynamic sensitivity of its afferents are discussed in relation to available data on stretch sensitivity.

Types of muscle fibers in the extraocular muscles of birds

Abstract Eye muscles of the quail, pigeon, sparrow and canary were examined histologically to see if their fibers are differentiated into two or more types, as has been described for mammals. In each oblique and rectus muscle examined, an area along the orbital border was found to be occupied by fibers of small cross-sectional area, and a more extensive central portion predominantly by large-caliber fibers. These fiber populations were separable on the basis of levels of α-glycerophosphate dehydrogenase and reduced nicotinamide adenine dinucleotide diaphorase activity, and to a lesser degree by glycogen content. All fibers stained strongly with the myosin adenosine triphosphatase reaction, the level of the activity being comparable to that in fast-twitch, mammalian limb muscles. The differences in features of location, size and histochemical reaction indicate that the rectus and oblique muscles in birds contain at least two types of fibers. The quadratus and pyramidalis muscles, which serve to advance the nictitating membrane, did not show segregation into zones of fibers, although in the pyramidalis two intermixed fibers were generally of larger size in the pyramidalis. Both fiber types stained darkly with myosin adenosine triphosphatase, suggesting that they were fast-twitch fibers.

Histochemical profiles of guinea-pig intrafusal fibres in normal muscles and after denervation, cordotomy and tenotomy

SynopsisHistochemical profiles of intrafusal fibres were analysed in normal muscles and in denervated, cordotomized and tenotomized preparations. Based on ATPase activity at polar regions, normal intrafusal fibres were classified as (I) ATPase-light fibres showing low or low-moderate activity when pre-incubated in either an acid or alkaline medium; (2) ATPase-dark fibres demonstrating high activity when preincubated in either an acid or alkaline medium and (3) ATPase-reversing fibres displaying low to moderate activity when pre-incubated in an acid medium, but showing high activity when pre-incubated in an alkaline medium. Four weeks after nerve section contrasting responses were seen between intrafusal fibre types. The ATPase-reversing fibres showed large decreases in polar cross-sectional area and NADH-diaphorase (NADH-D) activity, whereas fibres of the ATPase-light and ATPase-dark types were less subject to atrophy and their NADH-D levels were frequently increased. This differential effect suggests that ATPase-reversing fibres are trophically more dependent on neural innervation than ATPase-light and ATPase-dark fibres. After cordotomy and tenotomy no such marked differential responses were noted between fibre types.

Absence of muscle spindles in avian extraocular muscles

Abstract Complete serial sections of extraocular muscles from a quail, pigeon, English sparrow and canary were examined for the presence of muscle spindles. Oblique and rectus muscles of the eyeball, and the pyramidalis and quadratus muscles which activate the nictitating membrane were searched in each species. No spindles or other encapsulated endings were found, although such organs were easily detected in limb muscles from these birds.

Ionizing irradiation on development of the muscle spindle

Abstract Intrafusal (IF) fibers in leg muscles of the rat increase in number from two at birth, to three at day 3, and to the adult four fibers by the sixth day. The question of whether this multiplication and the attainment of the adult complement of fiber nuclei involves mitotic division was approached by subjecting one leg of rat pups to x-irradiation in single doses up to 1200 R, and comparing treated and control plantaris muscles on complete histological serial sections taken at 1 month of age. The mitotic process is particularly susceptible to ionizing irradiation and since periods for multiplication of IF fibers are fairly precisely scheduled, irradiation even in a single dose might be expected to disrupt future development. However, no effects were detected on number of spindles per muscle, on spindle complement of nuclear bag and chain fibers, or configuration of the nucleated region. Irradiation of gravid rats in the latter half of pregnancy with a single dose that was near lethal for the fetuses was also without obvious effect. Muscle spindles in several rat pups given single doses of colchicine were unaffected. Failure of these procedures to disturb spindle development supports the likelihood that the multiplication of IF fibers and allotment of nuclei that takes place in late natal and early postnatal periods is an amitotic process.

Adaptation to long-term stretch in the passive discharge of muscle spindles ☆

Abstract The effect of long-term stretch on the discharge of muscle spindles was studied by placing a cast on one hindlimb of cats so as to keep the calf region under moderate extension and after 2 to 6 weeks comparing responses of gastrocnemius afferents on casted and unrestrained sides to step wise extension of the muscle. The mean slope of the frequency-length relationship for populations of afferent fibers from immobilized limbs showed mixed effects. The slope was less in three animals, greater in three, and not significantly different in four. Three cats in which the calf region had been under stretch for only 3 to 5 days also demonstrated reduced sensitivity. In contrast, all cats in an earlier series in which the leg had been casted for 2 to 7 weeks with the calf muscles at resting length, showed greater stretch sensitivity. It is concluded that the spindle receptor adapts to long-term stretch of the muscle with a decrease in stretch sensitivity.

Effects of long-term increased gravitational load on intrafusal fibers on the avian muscle spindle.

Study of the effects of use-disuse on the muscle spindle began in 1897 when Morpurgo s examined spindles in the sartorius muscles of two dogs which had been exercised for 8 weeks on a treadmill. The few intrafusal fibers measured in biopsies taken in the control period and after exercise showed no difference in diameter, although means for extrafusal fibers differed by 40 ~ . Maynard and Tipton 7, with adequate sampling, found no significant difference in diameters of nuclear bag or chain intrafusal fibers in teres minor muscles f rom untrained rats and those exercised on a treadmill for 11 weeks. A decrease of 15 ~ , rather than an increase, in crosssectional area of one of the three histochemically identified intrafusal fiber types and no change in the other types was found by Botterman and Edgerton 1 in the soleus muscles of rats which ran for 17 weeks on a treadmill. On the other hand, Maier et al. 6, using tenotomy of synergistic muscles to elicit increased use, obtained a mild hypert rophy of intrafusal fibers in the cats gastrocnemius muscle. The mean diameter of nuclear bag fibers was increased by an average of 12 ~ in three animals, and extrafusal fibers by 34 ~ . Although in all of the above studies the extrafusal fibers had clearly hypertrophied, only with increased weight bearing due to tenotomy of synergists was an increase in intrafusal fiber size detected, and even in that study the percentage increase in intrafusal fiber area was much less than in extrafusal fibers. When, therefore, the opportunity arose to examine muscles which had been subjected to what ostensibly seems to be an even more rigorous form of loading, we thought it worthwhile to examine the spindles. These were leg muscles f rom chickens prepared by Burton et al. 3 in the course of study about the effects of chronic whole-body centrifugation on muscle maintenance. The adductor profundus femoris, an antigravity extensor muscle in the chicken,

Effects on Muscle Spindle Development of Multiple and Single Exposure to X-Irradiation

The effect on muscle spindle development of multiple exposure to x-irradiation was studied in the soleus and plantaris muscles of young rats. Growth in muscle volume and extrafusal fiber cross-sectional area was strongly reduced following exposures of 2400 to 4100 rad given within two weeks after birth. Spindles also demonstrated reduction in size of the nuclear bag and chain intrafusal fibers in the irradiated as compared to the contralateral muscle, but the difference was relatively less than that of the extrafusal fibers. The intracapsular space was reduced in some heavily irradiated spindles to the point where virtually no space was seen beneath the capsule wall. The number of clearly recognizable spindles was less in the heavily irradiated muscles. Essentially similar results were found in one rat given a single exposure to 4000 rad. The effects on the fibers are interpreted to indicate relative resistance to irradiation in development of the intrafusal musculature as compared to extrafusal fibers.