Growth factors and their receptors in the olfactory system

The olfactory epithelium is unique in the mammalian nervous system as it is a site of continual neurogenesis. Constant turnover of primary sensory neurons in the periphery results in continuous remodeling of neuronal circuits and synapses in the olfactory bulb throughout life. Most of the specific mechanisms and factors that control and modulate this process are not known. Recent studies suggest that growth factors, and their receptors, may play a crucial role in the development and continuous regeneration of olfactory neurons, i.e. particularly in neuronal proliferation, neurite outgrowth, fasciculation and synapse formation of the olfactory system. The potential role of the following factors and their receptors in different species are reviewed: Nerve growth factor (NGF); insulin-like growth factors (IGFs); fibroblast growth factors (FGFs); epidermal growth factor (EGF); transforming growth factor alpha (TGF alpha); amphiregulin (AR) and transforming growth factors beta (TGFs beta).