The avian olfactory system as a model for the analysis of apoptosis and cellular regeneration.

A reliable model, usable in vitro and in vivo, is necessary for analysis of processes engaged during cell death, regeneration and differentiation, The peripheral olfactory system is an attractive model for studying these proc esses through its dynamic neurogenesis that occurs continually throughout t he lifetime. Study aim: The aim of this study was the analysis of these processes on an animal model. Material and methods: We performed axotomy of the nerve olfactory on young animals and chicken embryos E17. Then we infused IGF-I (insulin-like growth factor-I) in the lesioned site. Death, regeneration and differenciation of cells were studied by immunocytology. Results: After hatching, the section of the olfactory nerve induced a rapid neuronal apoptosis at the 24th hour followed by a wave of mitosis 24 hours later. In prenatal stages, the response to the axotomy was rather similar to a dedifferentiation. In postnatal stages, the IGF-I infusion at the lesioned site had a triple f unction: survival of mature neurons, maintenance of differentiation and sti mulation of mitosis. The neoneurogenesis, which occured from neuronal stem cells would depend on the maturation and environment of the olfactory neuro ns protected from apoptosis by IGF-I. Conclusion: The avian olfactory epithelium is a good model for analysis of cell death, regeneration and differentiation. The capacity of these neurona l stem cells to dedifferentiate makes then more primitive than the pluripot ent cells, closer to totipotent embryonic stem cells. (C) 2001 Editions sci entifiques et medicales Elsevier SAS.