Table of Contents:
After a phase of proliferation and differentiation many neurons die during the development of the neuronal system. This ontogenetic neuron death cam be shown at numerous neuron populations of the central and peripheral nervous system. Neuronal death is regulated by neurotrophic factors (NTFs) which are produced by the target organs of the respective neurons. They reach the neurons through specific retrograde axonal transport. The first discovered and best examined neurotrophic factor is the nerve growth factor (NGF). The ontogenetic cell death in the ciliary ganglion is not influenced by NGF. The ontogenetic cell death in the ciliary ganglion of the embryonic chicken takes place between the embryonic days E8 and E14. About 50% of previously produced neurons die. So far no neurotrophic factor was known for this neuro population. Basic fibroblast growth factor (bFGF) enhances the survival of neurons in the ciliary ganglion in vitro. BFGF does also reduce the physiological cell death in vivo, when applied at the time of the ontogenetic cell death. 66% of normally dying neurons survive. This reduction of the ontogenetic cell death occurs directly and not indirectly by influencing glial or target organ proliferation. Examining the target organ, in this case the ciliary muscle in the eye, and the glia of the ciliary ganglion, no differences could be found as far as morphology and proliferation rate in bFGF-treated chicken embryos and control animals are considered. The classification of bFGF as a neurotrophic factor is discussed. This indicates that bFGF does not only show a substantial mitogenetic and angiongenetic effect. It can also play an important role in the regulation of the physiological neuron death.