Olfactory receptor neurons exist as distinct subclasses of immature and mature cells in primary culture

The processes of neuronal differentiation and survival are key questions in neurobiology. The olfactory system possesses unique regenerative capacity, as its neurons are continually replaced throughout adulthood from a mainta ined population of precursor cells. Primary cultures of olfactory epitheliu m enriched in olfactory neurons would provide a useful model to study the p rocesses of neurogenesis, differentiation and senescence. To determine whet her immature olfactory neurons could be isolated in primary culture and to investigate the mechanisms underlying these processes, culture conditions w hich selectively favored the presence of immature olfactory neurons were op timized. Using low plating densities, a population of cells was identified which, by reverse transcription-polymerase chain reaction, demonstrated mes sages for olfactory neuronal markers, including G(olf,), olfactory cyclic n ucleotide-gated channel and olfactory marker protein, as well as the p75 lo w-affinity nerve growth factor receptor. Immunocytochemical analysis showed that these putative immature olfactory neurons possessed immunoreactivity to G(olf,), neuron-specific tubulin, neural cell adhesion molecule, synapto physin and neurofilament. These neurons were defined as olfactory receptor neuron-1 cells. Under these conditions, a separate class of rarely occurrin g cells with different morphology demonstrated immunoreactivity to mature m arkers, such as adenylyl cyclase III and olfactory marker protein. Electrop hysiologically, these cells displayed properties consistent with those of a cutely dissociated olfactory receptor neurons. Another class of rarer cells which represented less than 2% of cells in culture demonstrated immunoreac tivity to glial fibrillary acidic protein. These cultures can serve as a model for in vitro analysis of olfactory rece ptor neuronal development and maintenance, and provide a potential substrat e for the development of cell lines. (C) 1999 IBRO. Published by Elsevier S cience Ltd.