Basic fibroblast growth factor immunoreactivity in the peripheral motor system of the rat.

We have used immunohistochemistry and electron microscopy to investigate the distribution of basic fibroblast growth factor (bFGF) in the peripheral motor system of the adult rat. In the lumbar segments of the spinal cord, bFGF immunoreactivity (bFGF-I) was seen in motor neurons and glial cells but not in axons. The neuronal immunostaining was seen as two or three intensely fluorescent spots in the nuclei with weak and more diffuse staining of the perinuclear cytoplasm. In the sciatic nerve, bFGF-I was seen in Schwann cells with strong intensity at the nodes of Ranvier. Axonal immunostaining could not be detected. At the electron microscopic level, the intense nodal immunostaining of Schwann cells was confirmed and was found to be localized to the Schwann cell membrane at the nodal gap. The intensity of staining decreased with distance from the node. In the soleus and gastrocnemius muscles, bFGF-I was seen at the motor endplates in sites corresponding to the motor nerve terminals in addition to faint staining within the muscle fibers. Electron microscopy showed that bFGF-I was localized within the nerve terminals. Histochemical localization of bFGF in the peripheral motor system is compatible with the functions ascribed for this protein in this system.