Fine structure of nerve processes containing basic fibroblast growth factor in muscle spindles of the rat masseter muscle.

An antiserum against basic fibroblast growth factor (bFGF) was characterized by immunoblot analysis and used to investigate the fine structure of bFGF-containing processes in muscle spindles of the rat masseter muscle. The bFGF antiserum recognized purified bFGF and bFGF-like materials with the same molecular weight as bFGF in crude homogenate of the brainstem from which bFGF fibers in the masseter muscle spindles presumably originate. Immunoelectron micrographs demonstrated that both proprioceptive and motor nerve endings in contact with intrafusal fibers contain bFGF. These findings suggest that bFGF of central (possibly trigeminal mesencephalic and motor nucleus) origin is transported into the muscle spindles subserving mechanoreception.