Neurotrophic factors in the primary olfactory pathway

The number of identified growth factors continues to increase rapidly with many being implicated in the development of the nervous system, although fo r most of them the autocrine and paracrine pathways of cellular regulation still remain to be elucidated. The primary olfactory pathway, consisting of the olfactory epithelium and olfactory bulb, is presented here as a very u seful model for the analysis of growth factor function. Review of the avail able literature suggests that a large proportion of neuroactive growth fact ors and their receptors are present in the olfactory epithelium or olfactor y bulb. Furthermore, the primary olfactory pathway is one of the most plast ic in the nervous system with neurogenesis continuing to contribute new sen sory neurones in the olfactory epithelium and new interneurones in the olfa ctory bulb throughout adult life. The rich diversity of growth factors and their receptors in the olfactory system indicates that it will be useful in elucidating how these molecules regulate the formation of the nervous syst em. The olfactory epithelium in particular is proving useful as a model for the actions of growth factors in directing the neuronal lineage from stem cell to mature neurone. (C) 2000 Elsevier Science Ltd. All rights reserved.