Denervation syndrome in the rat digastric muscle

Excitability parameters of m. digastricus muscle fibers were investigated in anesthetized (40 mg/kg of nembutal) rats 3-5 days after denervation. The number of fibers with high polarization level was increased as was the number of fibers with low and medium level in both bellies of m. digastricus. The differences in the level of polarization recorded in the muscle fibers of the abdominoposterior m. digastricus disappeared after denervation. It is suggested that denervation syndrome in m. digastricus deprived of spindle receptors was similar to that observed in other skeletal muscles.     

Change of digastric muscle length in feeding rabbits

An experiment was undertaken to measure directly the changing length of a jaw muscle during feeding in four intact, unanesthetized New Zealand White rabbits. Metal markers were implanted to define the anterior and posterior ends of the single belly of the digastric muscle and fluroscopic images were recorded on videotape while the animals fed on pelleted chow and carrot. Graphs of muscle length versus incisor separation were obtained by making measurements of single frames of the videotape record. The graphs revealed that when pelleted chow was being chewed the length of the diagastric muscle changed by no more than 9% of its greatest length; during the latter part of the closing stroke it changed very little. Incising and chewing carrot caused the digastric muscle to change in length continuously throughout the chewing cycle; incising carrot resulted in a 13% change in the length of the digastric muscle. The velocity of shortening is slightly less than one muscle length per second.     

Microelectrophysiological analysis of the fiber components of the rat digastric muscle

Membrane potential at rest (MP), action potential (AP), critical level of depolarization (CLD) and latent period (LP) of different muscle fibers were studied in two bellies of digastric muscle. Even and chaotic distribution of different muscle fibers was observed in the anterior and posterior belly, respectively. It is believed that electrophysiological data correspond to the results of histological analysis of muscle fibers in digastric muscle.     

Mechanism of paradoxical resistance of the digastric muscle to the action of tetanus toxin

Excitability parameters of m. masseter and m. digastricus fibers (resting minute potential--MP, action potential--AP, critical level of depolarization--CLD and rheobase currents) were determined in anesthetized rats (nembutal, 40 mg/kg) on days 3-4 and 10-15 after local intramuscular tetanus toxin injection (20 and 40 mouse Dlm, respectively). The development of local tetanus in m. masseter was characterized by typical excitability changes--a decrease in MP and AP. Local spasm in m. digastricus under analogous conditions of tetanus toxin injection was absent, while excitability tests demonstrated MP, AP and CLD augmentation. As m. digastricus motoneurons are devoid of inhibitory synaptic regions, these nervous cells are not affected by tetanus toxin.     

The fibre type composition of the striated muscle of the oesophagus in ruminants and carnivores

Summary The fibre type composition of the striated muscle layer of the oesophagus of the cow, sheep, donkey, dog and cat was examined with standard histochemical methods and immunohistochemical staining using type-specific antimyosin sera. The heavy chain and light chain composition of oesophageal myosin was also examined using electrophoretic peptide mapping and 2-dimensional gel electrophoresis respectively. In the ruminants and donkey the oesophagus was composed of fibre types I, IIA and IIC with immunohistochemical characteristics identical to those of the same fibre types found in control skeletal muscle. In the ruminants there was a gradient in the proportion of type I fibres from 1% (at the cervical end) to about 30% (at the caudal end).In the carnivores the oesophageal muscle was composed of a very small percentage of type I and IIC fibres, but the predominant type was very different hisotchemically and immunohistochemically from all the fibre types (I, IIA, IIB, IIC) present in the control muscles. This oesophageal fibre type (IIoes) had an acid- and alkaline-stable m-ATP-ase activity, a moderate histochemical Ca-Mg actomyosin ATPase activity, and reacted weakly with anti-IIA and antiIIB myosin sera. Although the light chains of the IIoes myosin were the same as the light chains of a mixture of IIA and IIB myosins, their respective heavy chains gave different peptide maps. Greater differences were obtained between the heavy chains of IIoes and other striated muscle myosins.These observations lead us to conclude that this predominant fibre type of the carnivore oesophageal striated muscle is of the fast type, and contains a distinct isoform of myosin similr but not identical to the other fast type myosins.     

The fibre type composition of the striated muscle of the oesophagus in ruminants and carnivores

The fibre type composition of the striated muscle layer of the oesophagus of the cow, sheep, donkey, dog and cat was examined with standard histochemical methods and immunohistochemical staining using type-specific antimyosin sera. The heavy chain and light chain composition of oesophageal myosin was also examined using electrophoretic peptide mapping and 2-dimensional gel electrophoresis respectively. In the ruminants and donkey the oesophagus was composed of fibre types I, IIA and IIC with immunohistochemical characteristics identical to those of the same fibre types found in control skeletal muscle. In the ruminants there was a gradient in the proportion of type I fibres from 1% (at the cervical end) to about 30% (at the caudal end). In the carnivores the oesophageal muscle was composed of a very small percentage of type I and IIC fibres, but the predominant type was very different histochemically and immunohistochemically from all the fibre types (I, IIA, IIB, IIC) present in the control muscles. This oesophageal fibre type ( IIoes ) had an acid- and alkaline-stable m-ATPase activity, a moderate histochemical Ca-Mg actomyosin ATPase activity, and reacted weakly with anti-IIA and anti-IIB myosin sera. Although the light chains of the IIoes myosin were the same as the light chains of a mixture of IIA and IIB myosins, their respective heavy chains gave different peptide maps. Greater differences were obtained between the heavy chains of IIoes and other striated muscle myosins. These observations lead us to conclude that this predominant fibre type of the carnivore oesophageal striated muscle is of the 'fast' type, and contains a distinct isoform of myosin similar but not identical to the other fast type myosins.     

Expression of unique and developmental myosin heavy chain isoforms in adult human digastric muscle.

Digastric muscle (DGM) is a powerful jaw-opening muscle that participates in chewing, swallowing, breathing, and speech. For better understanding of its contractile properties, five pairs of adult human DGMs were obtained from autopsies and processed with immunocytochemistry and/or immunoblotting. Monoclonal antibodies against alpha-cardiac, slow tonic, neonatal, and embryonic myosin heavy chain (MHC) isoforms were employed to determine whether the DGM fibers contain these MHC isoforms, which have previously been demonstrated in restricted specialized craniocervical skeletal muscles but have not been reported in normal adult human trunk and limb muscles. The results showed expression of all these MHC isoforms in adult human DGMs. About half of the fibers reacted positively to the antibody specific for the alpha-cardiac MHC isoform in DGMs, and the number of these fibers decreased with age. Slow tonic MHC isoform containing fibers accounted for 19% of the total fiber population. Both the alpha-cardiac and slow tonic MHC isoforms were found to coexist mainly with the slow twitch MHC isoform in a fiber. A few DGM fibers expressed the embryonic or neonatal MHC isoform. The findings suggest that human DGM fibers may be specialized to facilitate performance of complex motor behaviors in the upper airway and digestive tract.     

Evolution of skull shape in carnivores 1. Representative modern carnivores

Fifteen variables, selected primarily to reflect functionally significant aspects of cranial morphology, were measured on one skull each of 62 species of modern carnivores, including viverrids, canids, mustelids and felids. To allow comparisons between species of different sizes without the potentially confounding effects of allometric shape changes, the measurements were transformed to dimensionless variables, based on the residuals from allometric equations. Fourteen out of 15 of the transformed variables distinguish one or more of the four family groups and the rotated first two axes of a principal components analysis distinguish all four families from each other. The following functional hypotheses are proposed: mustelids and felids have the most powerful bites and canids the weakest among the four family groups studied; mustelids and, to a lesser degree, felids have more powerful neck musculature than do canids and viverrids; and visual abilities are best developed among felids and least developed among mustelids. The first two functional hypotheses suggest possible differences in killing behaviour, which are supported by a preliminary survey of the literature on such behaviour. Allometric analysis of the 15 cranial measures shows that the neurocranial components scale with negative allometry, while most of the other measures scale approximately isometrically.     

Evolution of skull shape in carnivores 2. Additional modern carnivores

Fifteen functionally significant aspects of skull morphology were measured on skulls of 36 additional species of carnivores to complete a survey of skull shape in modern fissiped (land) carnivores that includes most of the living genera. The measurements were transformed to dimensionless variables based on the residuals from allometric equations, and were analysed singly and in a 10 variable principal components analysis. An initial study of 62 species of viverrids, canids, mustelids and felids had shown those families to be distinguished from each other by the functionally significant measurements. However, among the additional 36 species, some procyonids, ursids and mustelids display a range of diversity of skull morphology that overlaps that of the other families and diminishes the potential value of the measurements as taxonomic characters. Intraspecific variation is presented for 12 species, and is low enough to allow use of some features as species level diagnostic characters. The lack of correlation between diet and functionally significant aspects of skull morphology among omnivorous carnivores, and the absence of certain skull shapes among carnivores are discussed.     

The effect of rate of distraction osteogenesis on structure and function of anterior digastric muscle fibers

The authors hypothesized that distraction at a rate of 3 mm/day, compared with mandibular distraction at a rate of 1 mm/day, would produce a maladaptive response in adjacent muscles of mastication. The authors further hypothesized that the maladaptive response would manifest at the single fiber level by means of increased sarcomeric heterogeneity, decreased maximum force output, and increased susceptibility to stretch-induced injury. In an ovine model, distraction osteogenesis of the right hemimandible was performed at either 1 mm/day for 21 days (n = 2) or 3 mm/day for 7 days (n = 2) to achieve a total distraction distance of 21 mm. The left hemimandibles served as controls. After a consolidation period of 2 days, the anterior digastric muscles were harvested; in six randomly selected single fibers from each muscle, maximum calcium-activated force (Po) was measured at optimal sarcomere length. The amount of damage to the sarcomeres in each fiber was assessed microscopically. To test susceptibility to contraction-induced injury, each fiber was given an activated stretch of 20 percent. Compared with control fibers and fibers distracted at 1 mm/day, maximum tetanic force (Po) was significantly lower in fibers distracted at 3 mm/day. Compared with control fibers, specific Po (Po/cross-sectional area) was lower in fibers distracted at 3 mm/day. The number of sarcomeres appearing damaged in fibers distracted at 3 mm/day was significantly higher than in control fibers or in fibers distracted at 1 mm/day. A greater deficit in Po was observed after a single activated stretch in fibers distracted at 3 mm/day than in control fibers or in fibers distracted at 1 mm/day. The authors conclude that distraction of the anterior digastric muscle in sheep at 3 mm/day produces a maladaptive response in the muscle fibers but a rate of 1 mm/day is tolerated by the muscle fibers. These data are consistent with the hypothesis that distraction of skeletal muscle at high rates results in increased heterogeneity of sarcomere lengths and that this increase in heterogeneity is the most likely potential mechanism resulting in whole muscle force deficits and in increased susceptibility to stretch-induced injury in distracted muscles.     

Analysis of histochemically and morphometrically in the anterior belly digastric muscle of osteopetrotic (op/op) mice.

The fibers of the anterior belly digastric muscle of mice, fed a granulated diet for various periods, have been studied histochemically and morphometrically. The diameters of the anterior belly digastric fibers in normal mice fed only a granulated diet were smaller than those in mice fed a solid diet. Differences in the succinate dehydrogenase (SDH) activity of muscle fibers between op/op and normal mice gradually appeared in the anterior belly digastric muscle and, by the age of 90 days, under-development of muscle fibers was observed in the mild-belly region of the anterior belly digastric muscle of op/op mice fed a granulated diet. These results indicate mechanical stress in mastication plays an important role in the development of the anterior belly digastric muscle structures.     

Comparative myology of the hominoid cranial base. I. The muscular relationships and bony attachments of the digastric muscle

This paper aims to document accurately the soft tissue anatomy and bony attachments of the posterior belly of the digastric muscle and other closely related muscles in the mastoid region of extant hominoids and fossil hominids. Five wet specimens including individuals of Pan, Gorilla and Pongo were dissected and described. Eight casts of fossil hominid cranial bases were also studied along with measurements and notes made from the same original fossil hominid specimens to assess their soft tissue markings in the light of the findings for the three great apes. The results indicate that whereas the attachment of the posterior belly of the digastric muscle in Homo sapiens is associated with a deep groove or fossa, it originates from a widened area and leaves no bony markings on the cranial base of the three great apes. Following a change in the position of the foramen magnum and the occipital condyles in hominids and H. sapiens the insertion of the posterior belly of the digastric has remained posteriorly positioned but has become compressed into a deep groove. It is likely that this has come about by the displacement of the more medial soft tissue structures which have been moved laterally away from the occipital condyles.     

microRNA在肌肉发育中的功能研究进展

microRNA(miRNA)是一类非编码的小RNA分子,它通过对靶mRNA的翻译抑制和降解对基因表达起负调节作用。现在人们已经清楚地知道miRNA参与了增殖、分化、凋亡、发育等许多生物过程。一些miRNA在肌肉中特异表达,参与肌肉发育。该文重点介绍了参与肌肉发育的miRNA。已有证据表明肌肉miRNA在肌肉的增殖和分化过程中起了重要的调节作用,miRNA的调节异常和肌肉疾病有关。因此,miRNA是一类新的肌肉调控因子,它有可能成为畜禽肉产量提高和肌肉相关疾病治疗的新型靶标。     

Anatomical anomaly of human digastric muscles

In the submandibular region an anatomical anomaly of muscle arrangement was found. Between the left and right digastric muscles, asymmetric accessory digastric muscles were detected, which all arose from the mandible and were attached to the hyoid bone. Furthermore, the right anterior digastric muscle had an accessory belly. These anomalies of digastric muscles may be anatomical manifestations of a functional support of the mylohyoid muscle.     

Serosurvey of small carnivores in the Bolivian Chaco

Five species of Bolivian carnivores, including nine Geoffroy's cats (Oncifelis geoffroyi), ten ocelots (Leopardus pardalis), one jaguarundi (Herpailurus yaguarondi), nine pampas foxes (Pseudalopex gymnocercus), and five crab-eating foxes (Cerdocyon thous) were sampled between March 2001 and April 2005 and tested for antibodies to common pathogens of domestic carnivores. Carnivores were trapped in three areas: a village, the region between human settlements and a protected area, and within Kaa-Iya National Park, Bolivia. Antibodies to canine distemper virus were detected in ocelots and pampas foxes. Antibodies to canine parvovirus were detected in pampas foxes and crab-eating foxes. Geoffroy's cats and all of the ocelots tested positive for antibodies to feline calicivirus (FCV), while fewer than half of Geoffroy's cats and no ocelots had antibodies to feline panleukopenia (FPV). These results confirm that these species of Bolivian carnivores are not na?ve to common pathogens of domestic carnivores, and seropositive animals were found in villages as well as in the national park.