Localization of Basic Fibroblast Growth Factor (bFGF)-like Immunoreactivity in Neural Circuits Innervating the Gastrocnemius Muscle, with Reference to the Direction of bFGF Transport

An antiserum against basic fibroblast growth factor (bFGF), characterized by immunoblot, was firstly used to immunolocalize bFGF-like materials in dorsal root ganglion (DRG) neurons, spinal motoneurons and their processes innervating the gastrocnemius muscle, and then secondly to determine the direction of bFGF transport in the processes by nerve ligation or nerve section experiments. Light and electron-microscopic immunohistochemistry revealed that significant numbers of DRG neurons (mainly of the large type), spinal motoneurons and their processes supplying the muscle are immunoreactive for bFGF, and that the bFGF neurons have diffuse immunoreaction deposits over the entire cytoplasmic areas except for the Golgi complex, mitochondria and microfilaments. Nerve terminals and glial processes with bFGF were rarely seen in contact with or in close apposition to the immunopositive neurons. At sixteen hours, 3 days and 7 days after unilateral ligation or transection of the sciatic nerve, bFGF fibers accumulated in a time-dependent way in the proximal but not in the distal stump; nerve transection caused a more intense accumulation of bFGF-immunoreactive fibers than did nerve ligation. These findings suggest that bFGF in large DRG neurons and motoneurons is transported anterogradely into the peripheral tissue, possibly without being incorporated into secretory granules or synaptic vesicles. They raise the possibility that bFGF within the transected nerve fibers is more actively conveyed during regeneration than in the ligated nerve fibers.