IMMUNOHISTOCHEMICAL CHARACTERIZATION OF HUMAN MASSETER MUSCLE-SPINDLES

An enzyme- and immunohistochemical study has been performed on human m asseter muscle spindles. Antibodies selective for different myosin hea vy chain (MHC) isoforms and M-band proteins (M-protein, myomesin, and MM-CK) were used. The expression of these proteins was determined in t he different intrafusal fiber types. Nuclear bag(2) and nuclear bag(2) fibers expressed predominantly slow-twitch and slow-tonic MHCs. The b ag(2) fibers in addition contained fetal MHC. Nuclear chain fibers coe xpressed embryonic, fetal, and fast-twitch MHCs. The bag, and chain fi bers contained all three M-band proteins, whereas the bag, fibers cont ained only myomesin. In general the MHC expression in the human masset er intrafusal fiber types was similar to that previously reported for limb muscles in man as well as for limb and masseter muscles in other species. However, the number of intrafusal fibers per spindle was unus ually high (up to 36). This reinforces the idea that masseter muscle s pindles have a strong proprioceptive impact during the control of jaw movements. (C) 1994 John Wiley and Sons, Inc.