Possible coordinated gene expressions for FGF receptor, FGF-5, and FGF-2 following seizures.

We have examined the influence of afferent activity that may trigger a coordinated response between ligands and their signal transduction receptors, as part of the regulation of the fibroblast growth factor (FGF) system. Epileptiform activity was induced by kainic acid injection, and in situ hybridization was used to assess the progress of changes in distribution and intensities of FGF receptor 1 (FGFR-1), FGF-5, and FGF-2 mRNAs. Our results showed that at early stages (3 h) afferent activity triggered a transient increase in both of the ligand mRNAs, whereas the receptor mRNA response was increased only in the dentate gyrus. At later stages, the FGFR-1 mRNA response was more complex, in which the various regions examined exhibited a broader range of values within the same time-points. This contrasted with the uniform pattern of FGF-5 and FGF-2 mRNAs responses, which in most of the brain regions examined showed a peak by 12 h following seizure induction and returned to normal values by 24 h. Immunohistochemistry showed an induction of FGFR-1 and FGF-2, 6 h postseizure induction which remained elevated up to 24 h later. The distinctive pattern of the FGFR-1 mRNA response appears to indicate that FGFR-1 is a factor in the modulation of the cellular response for FGF-5 and FGF-2. These results demonstrate that brain activity exerts influences at the gene expression levels of FGFR-1 and its ligands FGF-5 and FGF-2.