INCREASE OF BASIC FIBROBLAST GROWTH-FACTOR (BFGF, FGF-2) MESSENGER-RNA AND PROTEIN FOLLOWING IMPLANTATION OF A MICRODIALYSIS PROBE INTO RATHIPPOCAMPUS

In vivo microdialysis is an established tool for sampling extracellula r fluid compartments. However, microdialysis faces the problem that th e implantation of the probe damages the microenvironment from which me asurements are derived. In this study, we examined the expression of b asic fibroblast growth factor mRNA and protein at the cellular level a fter implantation of a microdialysis probe into the dorsal hippocampus and found that 8 h after inserting the probe bFGF mRNA was markedly i ncreased in a relatively large area centered around the probe, involvi ng both the dorsal hippocampus and the overlying cerebral cortex, as r evealed by radioactive in situ hybridization. Using nonradioactive in situ hybridization with digoxigenin-labelled riboprobes, combined with immunohistochemistry for glial fibrillary acidic protein we demonstra ted that bFGF mRNA was exclusively increased in astrocytes at the prob e insertion site. Using immunohistochemistry we also found that bFGF-l ike immunoreactivity was increased after implantation of the probe clo se to the lesion site: as shown by an increased number of bFGF immunor eactive nuclear glial profiles. These results provide evidence that th e implantation of a microdialysis probe into the brain induces activat ion of bFGF gene expression in astrocytes associated with nuclear bFGF -like immunoreactivity. We conclude that lesion-induced effects have t o be considered when evaluating microdialysis data, and that mechanica l trauma to the brain will activate astroglial trophism, as seen from the increased density of astroglial profiles demonstrating bFGF mRNA a nd protein levels.