Density of nerve fibres and expression of substance P, NR2B-receptors and nerve growth factor in healthy human masseter muscle: An immunohistochemical study

Abstract

Background: In skeletal muscle, free nerve endings are mostly located within the connective tissue. However, the distribution of sensory afferent fibres in healthy human masseter muscle tissues has not been studied. Objectives: Primarily to investigate human masseter muscle nerve fibre densities as well as expression of NR2B receptors, substance P (SP) and nerve growth factor (NGF), and secondarily to compare this between a) nerve fibres associated with myocytes and within connective tissue; b) sexes; and c) ages. Methods: Microbiopsies of the masseter muscle were obtained from 60 sex- and age-matched healthy participants. Biopsy sections were analysed using immunohistochemistry and were visualised with a Leica TCS SPE confocal microscope. The Mann-Whitney U test was used for statistical analyses. Results: The density of nerve fibres within connective tissue was significantly greater than in nerve fibres associated with myocytes (P