Reaction of striated fibers of human skeletal muscles to long-term anti-orthostatic hypokinesia

Eight men have been kept under a strict bed rest. The lower end of the bed has been elevated by 6 degrees. During the whole effect of the antiorthostatic hypokinesia (AOH) in biopsy of the skeletal muscle tissue no gross morphological changes and essential changes in relation of the muscle fiber (MF) types have been found. On the 120th day of AOH without application of any physical loading concentration of RNA, protein metabolism, glycogen, activity of the energetic metabolism enzymes, MF size decrease. Both contractile and energetic apparatus suffers essentially. This demonstrates certain atrophic processes in both types of the MF. Physical loading against the background of AOH, on the 120th day, prevents development of the atrophic processes in MF. This is demonstrated as maintenance of certain metabolic level and less pronounced changes of ultrastructure. On the 360th day of the experiment in the group without any loading, an essential atrophy of MF, a noticeable++ decrease in metabolism are observed. In the test group against the background of AOH the changes in the biopsy fibers are less pronounced and not so uniform. Application of physical loadings contributes to the development of certain adaptive reactions; their positive effect to the skeletal muscle fiber morphology depends on the structural background, against which it acts and their intensity. The earlier the load begins to act and the higher its intensity, the more pronounced is the delay in development of profound atrophic changes.     

Carbonic anhydrase isozyme distribution and characterization in metabolic fiber types of the dorsal levator muscle of the blue crab, Callinectes sapidus

Carbonic anhydrase (CA) distribution and characterization were examined in white and light pink fibers of the dorsal levator muscle of the blue crab. White fibers were structurally and metabolically characterized as fast twitch glycolytic, while the light pink fibers were fast oxidative. All subcellular fractions of both fiber types had significant levels of CA activity; cytoplasmic and microsomal activity was significantly higher in light pink vs white fibers. Cytoplasmic CA from both fiber types was highly sensitive to the inhibitors acetazolamide and chlorzolamide, with Ki values of approximately 2 and 0.4 nM, respectively. Further analysis confirmed that cytoplasmic CA from both fiber types was kinetically similar to the high turnover Type II isoform. It appears that the evolution of the CA Type III isoform, found in vertebrate red muscle, did not occur with the differentiation of metabolic fiber types in crustaceans. Membrane-associated CA, which was also kinetically similar to the Type II isoform, was 20-fold higher in light pink fibers, suggesting a physiological role in facilitated CO2 efflux from the muscle fiber during periods of prolonged maximal activity.     

Morphofunctional changes in the long tubular bones of animals which have developed while readapting after physical loads

The investigation has been performed on 120 white male rats of Wistar line. By means of the morphometry, electron microscopy and chemical methods dynamics of readaptive changes have been studied in long tubular bones during the period, when the effect of physical loadings both of dynamic and static character and of various intensity has been stopped, up to the old periods of the animals' life. Readaptation after moderate dynamic and static loadings is occurring for a long time and steadily. The changes caused by static loadings are nearly completely restored in a year. Morphofunctional rearrangements of the long tubular bones in the readaptation process after moderate dynamic loadings is characterized by residual manifestations. Prolonged readaptation after intensive physical loadings does not result in a complete restoration of all the parameters studied concerning growth and skeletal development. An intensive dynamic loading produces more stable changes, that are not subjected to a complete correction even after a passive readaptation for a year. Readaptation morphofunctional rearrangements of the long tubular skeletal bones depend on conditions of the previous regimen of the motor activity.     

Ultrastructural changes in the skeletal muscles after physical exertion in rats of various ages

The white rats of the age 1, 3 and 12 months ran in the treadmill at a speed 45 m/min for 20, 40, 60 and 90 days. There is not any linear dependence of muscular transformations and the intensity of physical loading. Changes of the material components of muscular fibers are of undulated character, depending on the age, increase in quantity of myofibrils is always accompanied with a decrease in the quantity of mitochondria. When the total share of myofibrils and mitochondria increases, the quantity of other ultrastructural elements of the muscular fibers and hyaloplasm decreases.     

Regulation of biosynthesis of secondary metabolites

The biosynthetic activity of mutants with altered morphological and biochemical characteristics, obtained from two strains ofStreptomyces aureofaciens by means of physical and chemical mutagens, was studied. The majority of mutants formed pigments different from pigments of the parent strains, which did not usually give fluorescence in UV-light and, in addition, differed as to the solubility in organic solvents. The production of further secondary metabolites was investigated chromatographically in the extracts from mycelium and in the fermentation fluid of submerged cultures. According to the results of chromatographical analysis, the obtained mutants can be divided into 12 metabolic types. In most of them the production of substances was found which are different both mutually and from the metabolites of parent strains in physical and chemical properties. A direct correlation was observed between the character of colonies and biosynthetic properties of mutants.     

Investigation of the functional characteristics of reticulo-spinal fibers of the ventral funiculus

Functional characteristics of single reticulo-spinal fibers of the ventral funiculi were studied at the level of the 10th thoracic segment of the spinal cord in anesthetized (with chloralose and pentobarbital) and decerebrate cats after removal of the cerebellum. The reticulospinal tract of the ventral funiculus consists of a broad spectrum of rhythmically active and "silent" fibers, divided into three groups: fibers with a high (65–110 m/sec), medium (45–60 m/sec), and low (20–40 m/sec) conduction velocity. Spontaneous rhythmic activity is more characteristic of the fibers of the last two groups. The quantitative ratio between rhythmically active and silent fibers was about twice as high in the decerebrate as in the anesthetized animals. Depending on the character of distribution of interspike intervals the spontaneous activity of the reticulo-spinal fibers of the animals of both groups could be classified in three types: I) with a uniform distribution of interval; II) with a tendency toward grouping of spikes into volleys; III) with marked grouping of the intervals. Fibers with low and medium conduction velocities more often had spontaneous activity of types I and II, while fibers with a high conduction velocity more often had activity of types II and III. The possible functional significance of the reticulo-spinal fibers of the ventral funiculi with different conduction velocities and types of spontaneous activity is discussed.     

Effects of hindlimb suspension on soleus muscle fibers and their spinal motoneurons in Wistar Hannover rats

Cross-sectional areas and succinate dehydrogenase (SDH) activities of soleus muscle fibers and their spinal motoneurons in male Wistar Hannover rats were determined after 16 days of hindlimb suspension. A decreased percentage of type I fibers and an increased percentage of type I+II fibers were observed after hindlimb suspension. Cross-sectional areas of all types of fibers were smaller in the hindlimb suspended than control rats. SDH activities of all types of fibers did not change after hindlimb suspension. Numbers, cross-sectional areas, or SDH activities of spinal motoneurons did not change after hindlimb suspension. It is suggested that spinal motoneurons innervating the rat soleus muscle are not affected by decreased neuromuscular activity on Earth and that gravity itself is important for maintaining of spinal motoneuron metabolic properties.     

Expression of muscle anabolic and metabolic factors in mechanically loaded MLO-Y4 osteocytes

Lack of physical activity results in muscle atrophy and bone loss, which can be counteracted by mechanical loading. Similar molecular signaling pathways are involved in the adaptation of muscle and bone mass to mechanical loading. Whether anabolic and metabolic factors regulating muscle mass, i.e., insulin-like growth factor-I isoforms (IGF-I Ea), mechano growth factor (MGF), myostatin, vascular endothelial growth factor (VEGF), or hepatocyte growth factor (HGF), are also produced by osteocytes in bone in response to mechanical loading is largely unknown. Therefore, we investigated whether mechanical loading by pulsating fluid flow (PFF) modulates the mRNA and/or protein levels of muscle anabolic and metabolic factors in MLO-Y4 osteocytes. Unloaded MLO-Y4 osteocytes expressed mRNA of VEGF, HGF, IGF-I Ea, and MGF, but not myostatin. PFF increased mRNA levels of IGF-I Ea (2.1-fold) and MGF (2.0-fold) at a peak shear stress rate of 44Pa/s, but not at 22Pa/s. PFF at 22 Pa/s increased VEGF mRNA levels (1.8- to 2.5-fold) and VEGF protein release (2.0- to 2.9-fold). Inhibition of nitric oxide production decreased (2.0-fold) PFF-induced VEGF protein release. PFF at 22 Pa/s decreased HGF mRNA levels (1.5-fold) but increased HGF protein release (2.3-fold). PFF-induced HGF protein release was nitric oxide dependent. Our data show that mechanically loaded MLO-Y4 osteocytes differentially express anabolic and metabolic factors involved in the adaptive response of muscle to mechanical loading (i.e., IGF-I Ea, MGF, VEGF, and HGF). Similarly to muscle fibers, mechanical loading enhanced expression levels of these growth factors in MLO-Y4 osteocytes. Although in MLO-Y4 osteocytes expression levels of IGF-I Ea and MGF of myostatin were very low or absent, it is known that the activity of osteoblasts and osteoclasts is strongly affected by them. The abundant expression levels of these factors in muscle cells, in combination with low expression in MLO-Y4 osteocytes, provide a possibility that growth factors expressed in muscle could affect signaling in bone cells.     

Histopathological changes and oxidative damage in type I and type II muscle fibers in rats undergoing paradoxical sleep deprivation

Backgroundprevious studies have shown that muscle atrophy is observed after sleep deprivation (SD) protocols; however, the mechanisms responsible are not fully understood. Muscle trophism can be modulated by several factors, including energy balance (positive or negative), nutritional status, oxidative stress, the level of physical activity, and disuse. The metabolic differences that exist in different types of muscle fiber may also be the result of different adaptive responses. To better understand these mechanisms, we evaluated markers of oxidative damage and histopathological changes in different types of muscle fibers in sleep-deprived rats.MethodsTwenty male Wistar EPM-1 rats were randomly allocated in two groups: a control group (CTL group; n = 10) and a sleep deprived group (SD group; n = 10). The SD group was submitted to continuous paradoxical SD for 96  h; the soleus (type I fibers) and plantar (type II fiber) muscles were analyzed for histopathological changes, trophism, lysosomal activity, and oxidative damage. Oxidative damage was assessed by lipid peroxidation and nuclear labeling of 8-OHdG.ResultsThe data demonstrated that SD increased the nuclear labeling of 8-OHdG and induced histopathological changes in both muscles, being more evident in the soleus muscle. In the type I fibers there was signs of tissue degeneration, inflammatory infiltrate and tissue edema. Muscle atrophy was observed in both muscles. The concentration of malondialdehyde, and cathepsin L activity only increased in type I fibers after SD.ConclusionThese data indicate that the histopathological changes observed after 96 h of SD in the skeletal muscle occur by different processes, according to the type of muscle fiber, with muscles predominantly composed of type I fibers undergoing greater oxidative damage and catabolic activity, as evidenced by a larger increase in 8-OHdG labeling, lipid peroxidation, and lysosomal activity.     

CYTOLOGICAL STUDIES OF FIBER TYPES IN SKELETAL MUSCLE : A Comparative Study of the Mammalian Diaphragm

A comparative investigation of the mammalian diaphragm has revealed a correlation between certain cytological aspects of red and white muscle fibers and functional activity. This skeletal muscle presents the advantage of a similar and constant function among the mammals, but its functional activity varies in a quantitative manner. Both the rate of breathing (and hence the rate of contraction of the diaphragm) and metabolic activity are known to be inversely related to body size; and this study has demonstrated a relationship between cytological characteristics of the diaphragm and body size of the animal. Small fibers rich in mitochondria (red fibers) are characteristic of small mammals, which have high metabolic activity and fast breathing rates; and large fibers with relatively low mitochondrial content predominate in large mammals, which have lower metabolic activity and slower breathing rates. In mammals with body size intermediate between these two groups (including the laboratory rat), the diaphragm consists of varying mixtures of fiber types. In general, the mitochondrial content of diaphragm fibers is inversely related to body size. It appears, then, that the red fiber reflects a high degree of metabolic activity or a relatively high rate of contraction within the range exhibited by this muscle.     

Training-induced alterations in young and senescent rat diaphragm muscle.

The current study sought to examine the effects of chronic endurance treadmill running on oxidative capacity and capillary density in specific diaphragm muscle fiber types in young (5 mo) and senescent (greater than or equal to 23 mo) female Fischer 344 rats. Both young and senescent animals trained at approximately 75% of maximal O2 consumption for 1 h/day 5 days/wk for 10 wk. Plantaris citrate synthase activity was significantly increased (P less than 0.01) in both young and old trained groups. Densitometric analysis of succinate dehydrogenase (SDH) activity in diaphragm type I, IIa, and IIb muscle fibers was done using a computerized image-processing system. There were no age-related differences in SDH activity between the young and old groups for any of the fiber types. In addition, SDH activity was found to be significantly increased (P less than 0.05) in all three fiber types in both the young and senescent trained animals compared with their sedentary counterparts. Fiber size and capillary density did not differ between young and senescent rats, nor did exercise affect this measure. Each fiber, irrespective of type, had an average of approximately four capillaries in contact with it. However, type IIb fibers had a significantly lower capillary density per unit area than type I or IIa muscle fibers. The results indicate that the senescent costal diaphragm maintains its ability to adapt to an increased metabolic demand brought about by locomotor exercise. Of further interest is the finding that training adaptations occurred in all three fiber types, suggesting that increased work of breathing from moderate exercise leads to recruitment of all three fiber types.(ABSTRACT TRUNCATED AT 250 WORDS)     

Metabolic capacity of individual muscle fibers from different anatomic locations.

We studied muscle fibers by quantitative biochemistry to determine whether metabolic capacity varied among fibers of a given type as a function of their anatomic location. Muscles were selected from both contiguous and diverse anatomic regions within the rats studied. The individual fibers, classified into myosin ATPase fiber types by histochemical means, were assessed for fiber diameters and analyzed for the activities of enzymes representing major energy pathways: malate dehydrogenase (MDH, oxidative), lactate dehydrogenase (LDH, glycolytic), and adenylokinase (AK, high-energy phosphate metabolism). We found that neither the average activities of each of the three enzymes nor the fiber diameters varied in Type I or Type IIa fibers selected from superficial to deep portions of the triceps surae of the hindlimb. However, the IIb fibers in the deep region of this muscle group had significantly greater oxidative capacity, less glycolytic capacity, and smaller diameters than the superficially situated IIb fibers. Type IIa fibers in lateral gastrocnemius, extensor digitorum longus, psoas, diaphragm, biceps brachii, superficial masseter, and superior rectus muscles were highly variable in both diameter and enzyme profiles, with a correlation between MDH activity and fiber diameter. Therefore, our results show that both intermuscular and intramuscular metabolic variations exist in muscle fibers of a given type.     

乳液法神经生长因子（NGF）电纺纤维的体外研究

目的：使用乳液法制备含有神经生长因子（NGF）的电纺纤维,研究其外观形貌和机械强度等物理性能,以及制备过程中NGF活性的变化,纤维中NGF的担载量和纤维体外释放动力学,评价其能否成为理想的神经修复材料,为进一步将NGF电纺纤维应用于周围神经修复奠定基础。方法：将NGF水溶液分散于PLLA溶液,通过W／O乳液法制备静电纺丝缓释纤维,对纤维的外观形貌等物理性能等进行表征,使用Elisa方法测定制备过程中NGF活性的保持以及体外释放动力学。结果：NGF电纺纤维具备类似细胞外基质（ECM）的良好外观形貌和一定的机械强度,其中NGF活性保持19．58％士6．05％,体外有效释放11天。结论：本文制备的乳液法NGF电纺纤维具备良好的物理性能,能够持续缓释有效剂量的NGF,适合作为神经修复材料进行进一步研究。     

Changes in the activity of succinate dehydrogenase in muscle fibers of functionally different muscles in the rat after a reduction in exertion--hypodynamia

In 105 male rats of Wistar strain distal parts of one of the thoracic extremities are amputated with keeping intact the places where the brachial muscle is fixed. This does not restrict the volume of the brachium movements but essentially decreases their dynamic component (power loading). For 45 days dynamics of succinate-dehydrogenase (SDG) activity is being revealed in muscle fibers (MF) of functionally different muscles: m. brachialis, m. serratus ventralis and m. triceps brachii (the medial head). Average tendency of the process, changes in the distribution margins, asymmetry and kurtosis are taken into account. Under hypodynamia reconstruction of the MF has a wavy character with a gradually longer period of fluctuations. In all the muscles appear MF with a greater than in the control SDG activity. In the medial head of the m. triceps brachii the fibers with the lowest SDG activity disappear. The amount of MF with the lowest activity decreases, while those with the higher--increases, the process being more pronounced in the m. triceps brachii. The amount of MF with middle activity of the enzyme remains nearly unchanged. MF with different initial enzymatic activity do not change simultaneously. The degree of the changes in the fibers and the power leading are connected with each other, the fibers with the low initial SDG activity including into the reaction at a sharper decrease of the latter. The changes in quantitative ratio of MF with different SDG activity are not the same in every muscle studied.     

Eye muscles of the pike (Esox lucius) fiber types and their actomyosin ATPase and SDH activity

The eye muscles of the pike are organized in two distinct populations of fibers arranged in semicircular layers. The distal layer, consisting of small diameter muscle fibers, is mainly made up of type I and tonic (slow) fibers. The central and proximal (facing the eyeball) parts of the eye muscles are occupied by IIB and IIC (fast) fibers. As a main criterion for identification of muscle fiber types, the reaction for actomyosin ATPase activity has been used: metabolic characterization of these fibers has been carried out on the basis of SDH activity.     

Changes in the electrical activity of the rabbit proximal colon in vivo by stimulation of the vagus and splanchnic nerves]

1. Using extracellular electrodes placed on the serosa, we recorded the modifications of the electrical activity of the colonic muslce fibers caused by the stimulation of vagal and splanchnic nerve fibers. 2. Vagal stimulation produces two types of junction potentials: excitatory junction potentials (EJPs) and inhibitory junction potentials (IJPs). The IJPs are elicited by stimulation of vagal fibers which innervate intramural non-adrenergic inhibitory neurons. 3. The conduction velocity of the nerve impulse along the vagal pre-ganglionic fibers is 1.01 m/sec for excitatory fibers and 0.5. m/sec for inhibitory fibers. 4. Splanchnic fiber stimulation causes EJP disappearance, blocking transmission between preganglionic fibers and intramural excitatory neurons, and a decrease in IJP amplitude that most likely indicates a previous hyperpolarization of the smooth muscle. 5. IJP persistence during splanchnic stimulation proves that sympathetic inhibition does not modify the transmission of the vagal influx onto the non-adrenergic inhibitory neurons of the intramural plexuses. 6. Through a comparative study of proximal and distal colonic innervation, we are able to show that there is a similar organization of both regions, that is a double inhibitory innervation: an adrenergic one of a sympathetic origin, and a non adrenergic one of a parasympathetic origin.     

A theory of steady-state activity in nerve-fiber networks: I. Definitions and preliminary lemmas

As an essay towards the determination of the effect of structural relations among nerve fibers upon the character of their activity, preliminary consideration is given to the steady-state activity of some simple neural structures. It is assumed as a first approximation that while acted upon by a constant stimulus, each fiber reaches a steady-state activity whose intensity is a linear function of the applied stimulus. It is shown by way of example that for a simple two-fiber circuit of inhibitory neurons knowledge of the stimuli applied to the separate fibers does not necessarily suffice to determine uniquely the activity that will result. On the other hand, there are deduced certain restrictions on the possible types of activity that may be consistent with a given pattern of applied stimulation.     

Myofibrillar distribution of succinate dehydrogenase activity and lipid stores differs in skeletal muscle tissue of paraplegic subjects

Lack of physical activity has been related to an increased risk of developing insulin resistance. This study aimed to assess the impact of chronic muscle deconditioning on whole body insulin sensitivity, muscle oxidative capacity, and intramyocellular lipid (IMCL) content in subjects with paraplegia. Nine subjects with paraplegia and nine able-bodied, lean controls were recruited. An oral glucose tolerance test was performed to assess whole body insulin sensitivity. IMCL content was determined both in vivo and in vitro using (1)H-magnetic resonance spectroscopy and fluorescence microscopy, respectively. Muscle biopsy samples were stained for succinate dehydrogenase (SDH) activity to measure muscle fiber oxidative capacity. Subcellular distributions of IMCL and SDH activity were determined by defining subsarcolemmal and intermyofibrillar areas on histological samples. SDH activity was 57 ± 14% lower in muscle fibers derived from subjects with paraplegia when compared with controls (P < 0.05), but IMCL content and whole body insulin sensitivity did not differ between groups. In muscle fibers taken from controls, both SDH activity and IMCL content were higher in the subsarcolemmal region than in the intermyofibrillar area. This typical subcellular SDH and IMCL distribution pattern was lost in muscle fibers collected from subjects with paraplegia and had changed toward a more uniform distribution. In conclusion, the lower metabolic demand in deconditioned muscle of subjects with paraplegia results in a significant decline in muscle fiber oxidative capacity and is accompanied by changes in the subcellular distribution patterns of SDH activity and IMCL. However, loss of muscle activity due to paraplegia is not associated with substantial lipid accumulation in skeletal muscle tissue.