Localization of bFGF and FGF-receptor in the developing nervous system of the embryonic and newborn rat.

We examined the localization of basic fibroblast growth factor (bFGF) in the developing embryonic and newborn rat nervous system using 2 anti-bFGF antibodies. Embryonic (E13, E14, E15, E16, E17, and E18) and newborn tissues were examined. Between E16 and E17 strong bFGF immunoreactivity (IR) was detectable in the cortex and striatum and, in addition, in almost all neurons of the brainstem, spinal cord, and spinal ganglia. In contrast, in the newborn rat bFGF-IR was found in neuronal subpopulations of brainstem nuclei, ventral spinal cord, and spinal ganglia as it is known for the respective postnatal/adult parts of the nervous system. At E16 7.0 kb and 3.7 kb bFGF mRNA were present. The identification of bFGF-responsive cells was performed using immunocytochemistry (anti-flg antibody) and 125I bFGF for binding studies. The neuronal localization of FGF-receptor suggests that bFGF mediates its effects in an autocrine or paracrine manner. At the time of strongest bFGF-staining (E16/17), proliferation of neurons is almost completed in most of the nervous system areas. Therefore, it could also be suggested from previous biological experiments that the physiological functions of bFGF could include trophic and/or differentiating effects on developing neurons rather than mitogenic effects. The change of the bFGF-staining pattern after birth could indicate a change in the physiological function of bFGF, i.e., different bFGF effects in the immature and mature nervous systems.