Chronic Low-Frequency Stimulation Transforms Cat Masticatory Muscle Fibers into Jaw-Slow Fibers

Abstract

SummaryCat masticatory muscle during regeneration expresses masticatory-specific myofibrillar proteins upon innervation by a fast muscle nerve but acquires the jaw-slow phenotype when innervated by a slow muscle nerve. Here, we test the hypothesis that chronic low-frequency stimulation simulating impulses from the slow nerve can result in masticatory-toslow fiber-type transformation. In six cats, the temporalis muscle was continuously stimulated directly at 10 Hz for up to 12 weeks using a stimulator affixed to the skull. Stimulated muscles were analyzed by immunohistochemistry using, among others, monoclonal antibodies against masticatory-specific myosin heavy chain (MyHC), myosin binding protein-C, and tropomyosins. Under the electrodes, stimulation induced muscle regeneration, which generated slow fibers. Deep to the electrodes, at two to three weeks, two distinct populations of masticatory fibers began to express slow MyHC: 1) evenly distributed fibers that completely suppressed masticatory-specific proteins but transiently co-expressed fetal MyHCs, and 2) incompletely transformed fibers that express slow and masticatory but not fetal MyHCs. SDS-PAGE confirmed de novo expression of slow MyHC and β-tropomyosin in the stimulated muscles. We conclude that chronic low-frequency stimulation induces masticatory-to-slow fiber-type conversion. The two populations of transforming masticatory fibers may differ in their mode of activation or lineage of their myogenic cells. (J Histochem Cytochem 59:849-863, 2011)

Developmental, Physiological and Phylogenetic Perspectives on the Expression and Regulation of Myosin Heavy Chains in Craniofacial Muscles

“…The induction of β-slow MyHC and the suppression of masticatory MyHC in regenerated cat temporalis muscle innervated by the limb slow nerve [97,98] suggest that these changes are brought about by CLFS mediated by the tonic motoneurons innervating slow limb muscle. This has been confirmed by the transformation of masticatory fibres into jaw slow fibres through CLFS of the cat temporalis muscle [220]. It is likely that the molecular mechanism involved here is the same as that which transforms limb fast fibres into β-slow fibres.…”

“…Neural impulse patterns regulate MyHC expression in craniofacial muscles as in somitic muscles, enabling them to adjust their properties to changing functional demands during the lifetime of the animal. CLFS, which leads to the expression of β-slow MyHC in susceptible limb muscle allotypes, also induces β-slow MyHC expression in masticatory fibres of jaw muscles [220] and in sheep laryngeal muscle [300]. The different impulse patterns for the regulation of specific fast MyHCs in limb muscles probably also apply to craniofacial muscles competent in expressing these MyHCs.…”

Myosin heavy chains in extraocular muscle fibres: Distribution, regulation and function

“…174 A muscle's repertoire for MyHC expression is thus determined by the lineage of its myogenic cells, while the neural impulse pattern specifies the isoform expressed within this repertoire. 175 Myogenic regulation of MyHC expression is further supported by cross-innervation studies between muscles of different allotypes. Rat thyroarythenoid, a laryngeal muscle derived from sixth branchial arch which expresses only the fast 2X, 2B and EO MyHCs, while the sternohyoid, a somite-derived muscle has a limb MyHC profile.…”

“…However, masticatory MyHC is also expressed in aneural jaw muscle regenerates 173 and in cultures of satellite cells from masticatory muscle 174 . A muscle's repertoire for MyHC expression is thus determined by the lineage of its myogenic cells, while the neural impulse pattern specifies the isoform expressed within this repertoire 175 …”

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