Ontogeny of histochemical fiber types and muscle function in the masseter muscle of miniature swine

Abstract

In this study of masticatory maturation, the ontogeny of the histochemical fiber type composition of musculus masseter is examined in the omnivorous miniature swine (Sus scrofa). Fiber type characteristics are interpreted by comparison with electromyography (EMG) recorded during feeding behavior. Similar to locomotion studies, the results suggest a correspondence between the composition and arrangement of motor units and their recruitment pattern. Serial sections of masseter muscles from 10 minipigs, ranging from 2 weeks to slightly over 1 year of age, were stained for myosin adenosine triphosphatase (mATPase) activity to distinguish slow-twitch from fast-twitch fibers, and for nicotinamide adenosine dehydrogenase-tetrazolium reductase to assess the aerobic capacity of the same fibers. Although maintaining a uniformly high aerobic capacity throughout ontogeny and in adult animals, a transition is observed in the relative proportions of fast- and slow-twitch fibers. The primarily fast-twitch neonatal pig masseter eventually comprises approximately 25-30% slow-twitch fibers in adults, with a higher predominance of slow fibers in the deep (vs. superficial) and anterior (vs. posterior) regions of the muscle. Furthermore, while individual fibers of adult masseters generally stain for either alkaline- or acid-stable mATPase activity, a substantial proportion of cells in developing animals exhibits the presence of both isozymes. EMG results indicate functional heterogeneity within the masseter of adult pigs. During chewing, when pig chow is replaced by cracked corn, EMG activity in the deep portion of the muscle either decreases or increases slightly. In the superficial portion, however, muscle amplitudes become dramatically higher for corn, surpassing levels generated for chewing the less obdurate chow. These results are consistent with a behavioral transition from neonatal suckling to sustained mastication of foods of more complex textures eaten by adult pigs. The relationship between these fiber type and EMG results for pig masseter corresponds to those pertaining to motor unit recruitment in the extensor muscles of locomotion. Implications of this work for the evolutionary morphology of mastication also are discussed.

Modulation of mandibular loading and bite force in mammals during mastication

“…In mammalian masticatory muscles, as in the locomotor muscles, force modulation at low force amplitudes appears to be predominantly via muscle fiber recruitment rather than rate modulation (Goldberg and Derfler, 1977;Hannam and McMillan, 1994;Scutter and Türker, 1998). Mammalian masticatory muscles are not uniform in their fiber types (Anapol and Herring, 2000;Herring, 1994;Maxwell et al, 1979;Wall et al, 2006;Wall et al, 2005), and a large number of studies suggest that smaller, slower motor units are recruited before larger, faster motor units (Clark et al, 1978;Desmedt and Godaux, 1979;Goldberg and Derfler, 1977;LevTov et al, 1993;Lund et al, 1979;Miles and Türker, 1986;Miles et al, 1987;van Eijden and Turkawski, 2001;Van Wessel et al, 2005;Wall et al, 2006;Wall et al, 2005;Yemm, 1977). Thus, the evidence suggests that the generation of progressively higher bite forces during rhythmic mastication is achieved through increased recruitment of larger, faster motor units, resulting in increases in the rate of the generation of muscle force.…”

Rskα-actin/hIGF-1 transgenic mice with increased IGF-I in skeletal muscle and blood: Impact on regeneration, denervation and muscular dystrophy

“…Histochemical staining of skeletal muscle of transgenic and wild-type mice was independently performed by two laboratories, using nicotinamide adenine dinucleotide -nitro-blue tetrazolium (NADH-TR) or succinic dehydrogenase (SDH). Staining with NADH-TR and SDH yield comparable results [22] and are used to differentiate fast, intermediate and slow type myofibres [23,24]. Histochemistry with NADH-TR was performed on the limb muscle (EDL, TA and gastrocnemius) of 3-month old transgenic and wild type mice following described procedures [25].…”

Regional variation in IIM myosin heavy chain expression in the temporalis muscle of female and male baboons (Papio anubis)

“…A number of workers have hypothesized that the differential distribution of fast/type II fibers within chewing muscles, which tend to be concentrated in the superficial parts of muscles such as the masseter and temporalis, is a specialization for the rapid production of high occlusal force during the power stroke of mastication (Anapol and Herring, 2000; Gibbs et al, 1983; Herring, Grimm, and Grimm, 1979; Nielsen and Miller, 1988). The high occlusal force hypothesis is consistent with the suggestion that expression of type IIM (masticatory) MyHC, because of its high force generating ability relative to other fast MyHCs, is often correlated with dietary specializations that require high occlusal forces during prey capture or hard/tough object feeding (Hoh, 2002; Hoh et al, 2006; Yamaguchi, 2007; Reiser et al, 2009; Toniolo et al, 2008).…”