Maintenance of Intermediolateral Spinal Cord Neurons by Fibroblast Growth Factor Administered to the Medullectomized Rat Adrenal Gland: Dependence on Intact Adrenal Innervation and Cellular Organization of Implants

We have previously shown that basic fibroblast growth factor (bFGF; 2 microg), when administered in gelfoams implanted to medullectomized adult rat adrenal glands, maintains target-deprived preganglionic neurons located in the intermediolateral column (IML) of the spinal cord. We show now that administration of 600 or 60 ng/implant/organ of the biologically active recombinant protein also maintains IML-neurons. The effects depend on an intact organ nerve supply since administration of bFGF-implants to the medullectomized and denervated (splanchnicotomized) organ abolishes the maintenance effects for IML-neurons. A possible regeneration of cholinergic nerve fibres was assessed by quantitative determination of choline acetyltransferase (ChAT)-activity and ultrastructurally under various treatments. When compared to a cytochrome-(Cyto)-C treatment, bFGF significantly increased ChAT-activity in the innervated adrenal gland after 4 weeks, suggesting that sprouting of cholinergic nerve fibres and/or recovery of enzyme activity had occurred. Electron microscopically, unmyelinated axons associated with Schwann cells were only found in bFGF, but not in Cyto-C-implants. We conclude that exogenous bFGF or a yet unidentified trophic molecule possibly induced by bFGF in the adrenal gland acts as a retrogradely transported messenger serving for the maintenance of spinal cord IML-neurons in vivo. By stimulating axonal sprouting, bFGF might facilitate access of trophic material to nerve fibres.