Morphological aspects of rabbit masseter muscle after cervical sympathectomy

Abstract

The objective of this paper was to study the effect of sympathetic innervation on morphological and histochemical aspects of skeletal muscle tissue. Rabbit masseter muscle was studied using histochemical and immunohistochemical methods for periods of up to 18 months post-sympathectomy. The morphological and enzymatic characteristics of control masseter muscles were similar on both the left and right sides. The main features were muscle fibres with a mosaic pattern and a predominance of type IIa fibres, followed by type I. Type IIb fibres showed very low frequency. Sympathectomized animals showed varying degrees of metabolic and morphological alterations, especially 18 months after sympathectomy. The first five groups showed a higher frequency of type I fibres, whilst the oldest group showed a higher frequency of type IIb fibres. In the oldest group, a significant variation in fibre diameter was observed. Many fibres showed small diameter, atrophy, hypertrophy, splitting, and necrosis. Areas with fibrosis were observed. Thus cervical sympathectomy induced morphological alterations in the masseter muscles. These alterations were, in part, similar to both denervation and myopathy. These findings indicate that sympathetic innervation contributes to the maintenance of the morphological and metabolic features of masseter muscle fibres.

Figure 1

Control masseter muscle. a – Normal fibres. HE, × 80. b and c – Three types of muscle fibre (I, IIa, IIb) with mosaic pattern. NADH-TR, × 100 and Non-specific Esterase, × 80, respectively. d – Predominance of type IIa fibre. m-ATPase, pH 4.6, × 60. e and f – Immunohistochemical reaction with monoclonal antibody for slow myosin, × 80, and fast IIa myosin, respectively, × 80.

Figure 2

Masseter muscle after sympathectomy. a – Atrophic (A) and hypertrophic (H) fibres. Fibrosis (F). Splitting (arrow). HE, × 80. b – Necrotic fibres (N). Internal nucleus (Nu). HE, × 80. c – Atrophic (A) fibres. Adipose tissue (Ad). Gomori Stain, × 60. d – Fibre clusters with intense oxidative enzyme activity (*), and fibres with alteration in oxidative enzyme activity (arrow head). Atrophic fibre (f). NADH-TR. X60. e – Angulated atrophic fibre (f). Non-specific esterase, × 60. f – Clusters of type I (I) fibre. m-ATPase, pH 4.6. × 40.