Morphological aspects of rabbit masseter muscle after cervical sympathectomy

The objective of this paper was to study the effect of sympathetic innervat ion on morphological and histochemical aspects of skeletal muscle tissue. R abbit masseter muscle was studied using histochemical and immunohistochemic al methods for periods of up to 18 months post-sympathectomy. The morpholog ical and enzymatic characteristics of control masseter muscles were similar on both the left and right sides. The main features were muscle fibres wit h a mosaic pattern and a predominance of type IIa fibres, followed by type I. Type IIb fibres showed very low frequency. Sympathectomized animals show ed varying degrees of metabolic and morphological alterations, especially 1 8 months after sympathectomy. The first five groups showed a higher frequen cy of type I fibres, whilst the oldest group showed a higher frequency of t ype IIb fibres. In the oldest group, a significant variation in fibre diame ter was observed. Many fibres showed small diameter, atrophy, hypertrophy, splitting, and necrosis. Areas with fibrosis were observed. Thus cervical s ympathectomy induced morphological alterations in the masseter muscles. The se alterations were, in part, similar to both denervation and myopathy. The se findings indicate that sympathetic innervation contributes to the mainte nance of the morphological and metabolic features of masseter muscle fibres .