Characteristics of paravertebral muscles - fibre type distribution pattern in the pika, Ochotona rufescens (Mammalia: Lagomorpha)

Abstract

The evolution of the locomotor apparatus in vertebrates is marked by major reorganizations in trunk's musculature. The hypothesized functions of mammalian back muscles in the literature are discussed under consideration of the distribution and proportion of oxidative, type-I-fibres, oxidativeglycolytic, type-IIa-fibres and glycolytic, type-IIb-fibres in paravertebral muscles of a small mammal. The fibre type distribution was examined from a complete series of histological sections maintaining topographical relationships between the muscles as well as within the muscle, in order to establish the overall distribution pattern. The deep and short muscles showed the highest percentage of oxidative fibres. The larger, superficial paravertebral muscles contained the highest percentage of glycolytic fibres. Two muscles were intermediate in their proportion of fibre types. All epaxial muscles together can be interpreted as an antigravity muscle-complex counteracting enduringly against the rebound tendency caused by gravitation, comparable with antigravity muscles in limbs. A gradient from deep to superficial, or a clear regionalization of oxidative muscle fibres in central deep regions around a large intramuscular tendon was found in the m. spinalis and the m. quadratus lumborum, respectively. Concepts of the function of human back muscles as those of A. Bergmark (1989: Acta Orthop. Scand. 230, 1) or S.G.T. Gibbons & M.J. Comerford (2001: Orthop. Division Rev.March/April, 21) were exposed to be more general within mammals. Functional specializations of different muscles and muscle parts are discussed under the consideration of evolutionary reorganization of the paravertebral musculature in tetrapods.Along the cranio-caudal axis, the percentage of oxidative fibres was decreased in caudal direction within the same muscles, whereas the proportion of glycolytic fibres was increased. Therefore, classifications of muscles as ÔglycolyticÕ or ÔoxidativeÕ based on biopsies or analyses of single cross-sections may result in wrong interpretations. Changes in the proportions of the fibre type distribution pattern were mostly due to oxidative and glycolytic fibre types, whereas the percentage of oxidative-glycolytic fibres had only minor influence. A significant positive correlation between the cross-sectional area of the single fibre and its percentage in the area investigated were observed for oxidative fibres, whereby the size was positive correlated to the proportion of the oxidative fibres.

Distribution Pattern of Muscle Fiber Types in the Perivertebral Musculature of Two Different Sized Species of Mice

“…Concurrently, the muscular area containing Type I fibers, relative to the csa of the perivertebral musculature, increased caudad starting around the mid-lumbar region in both mice (laboratory mouse: L3: 0.4%, L6: 11%, harvest mouse: L3: 1.4%, L6: 14%). This overall cranio-caudal increase in the oxidative capacity is in contrast to previous observations in the pika, in which, for example, the percentage of Type I fibers decreased in the superficial muscles (Schilling, 2005). In the deep Type I rich muscles, a cranio-caudal increase of the Type I fiber proportion was observed in the pika as well but was less dramatic (only up to the twofold).…”

“…The region comprises the subvertebral muscles completely, with the most cranial slips of the m. quadratus lumborum inserting onto T12 and T12/13, respectively. Furthermore, comparable data exist for a whole series of small mammals from previous studies (Schilling, 2005;Schilling et al, 2005;Moritz et al, 2007;Schilling, 2009). Serial cross sections at the level of the intervertebral discs and the middle of the vertebrae were selected and digitized using a ColorView12 digital camera mounted to an Axioplan microscope (Zeiss V R ).…”

“…Similarly, a very high proportion of intermediate fibers for the m. soleus, a slow stabilizer of the ankle joint dominated by Type I fibers in other mammals (e.g., rat, guinea pig, cat : Close, 1972;guinea pig, rabbit: Peter et al, 1972;diverse: Pearson and Young, 1989) was reported for different shrew species (93%: Type IIA fibers in the Asian musk shrew, Suzuki, 1990; 98% Type IID fibers in the Eurasian common shrew, Savolainen and Vornanan, 1995; 100% IID fibers in the Etruscan shrew, Peters et al, 1999). In all muscles, including the ones that show clear regionalizations of the other two fiber types, Type IIA fibers were more or less homogeneously distributed throughout the cross section (Carlson, 1978;Schilling, 2005;Moritz et al, 2007;this study). This finding and the strikingly high proportion of Type IIA fibers particularly in the harvest mouse (ca.…”

“…Recording the muscle's activity during respiration, Boyd et al (1965) suggested that the m. quadratus lumborum stabilizes the last ribs to provide a punctum fixum for the contracting, flattening diaphragm during inspiration. The regionalization of the muscle has been discussed in relation to the possible function of the muscle in supporting lung ventilation in addition to mobilizing as well as stabilizing the vertebral column (Schilling, 2005;Schilling, 2009). The high proportion of fatigue resistant, oxidative fibers in the cranial part of the muscle is well suited to fulfill this function.…”

“…The mm. interspinales, the axial muscles with the overall highest Type I proportion, contained up to 88% Type I fibers in the pika (226 g: Schilling, 2005) and more than 90% in the rat (229 g: Schilling et al, 2005), but comprised only 63% in the laboratory mouse and not more than 20% in the harvest mouse. The maximum Type I fiber percentages were >90%, >90%, 47%, and 15%, respectively, in the deep region of the m. multifidus and >90%, >90%, 35%, and 7% in the mm.…”