COMPARATIVE LOCALIZATION OF FIBROBLAST GROWTH-FACTOR RECEPTOR-1, RECEPTOR-2, AND RECEPTOR-3 MESSENGER-RNAS IN THE RAT-BRAIN - IN-SITU HYBRIDIZATION ANALYSIS

The present study provides a detailed comparative description in the a dult rat brain of areas that express mRNAs coding for the fibroblast g rowth factor subtype receptors 1-3 (FGFR1-3). One observation in this analysis was a widespread expression in the brain of all three FGFR mR NAs, according to the following rank order: FGFR1, diencephalon < tele ncephalon < mesencephalon and metencephalon < myelencephalon; FGFR2 an d FGFR3, telencephalon < diencephalon < mesencephalon and metencephalo n < myelencephalon. Another observation was an apparent cellular speci ficity in their basal expression. Thus, the FGFR1 mRNA was expressed m ainly in large and weakly stained cells, whereas FGFR2 transcripts wer e expressed primarily in small and strongly stained cells and in cells of brain regions devoid of neuronal cells, such as the white matter. FGFR3 mRNA was always detected in small and strongly stained cells wit h scattered distribution and was not expressed in the white matter. Ho wever, FGFR2 mRNA was weakly expressed also in large cells localized i n some nuclei of the lower brainstem, in the diagonal band, and in the septum. Furthermore, in the medial habenula and in the nuclei of the pens, there exists a high density of cells expressing both FGFR1 and F GFR2 (60-100%). With neurotoxic lesions involving 6-hydroxy-dopamine m icroinjections in the substantia nigra, reactive glial cells in the le sioned area and surrounding the cannula tract showed an increase in th e expression of both FGFR1 and FGFR2 mRNAs, whereas no increased expre ssion was found for FGFR3 mRNA. Taken together, these findings showed that these three FGF receptors exist in all subtypes of cells of each brain region. Their apparent cellular specificity suggests that these receptor subtypes can have a differential trophic role in the brain, r eflecting the various biological activities shown by the ligands of th e FGF family. (C) 1997 Wiley-Liss, Inc.