IN-VITRO INDUCTION OF APOPTOSIS OR DIFFERENTIATION BY DOPAMINE IN AN IMMORTALIZED OLFACTORY NEURONAL CELL-LINE

A new neuronal cell line was generated by transfection of rat olfactor y epithelium with immortalizing recombinant oncogene E1A of adenovirus -2. The resulting 13.S.1.24 line of transformed cells expressed an ant igenic phenotype of olfactory neuronal progenitors. Addition of dopami ne to 13.S.1.24 cultures induced reduction of cell number within 2 day s. Two hallmarks of apoptosis were detected in dopamine-treated cultur es: internucleosomal DNA fragmentation and nuclear condensation. Dopam ine did not alter the cell proliferation rate, as assessed by [H-3]thy midine incorporation. Dopamine also stimulated differentiation of surv iving 13.S.1.24 cells into bipolar olfactory marker protein-immunoreac tive neurons, Time-dependency assessments over 1 week of treatment ind icated that apoptosis and differentiation induced by dopamine were con comitant, Both apoptosis and differentiation triggered by dopamine wer e dose-dependent, half-maximal effects being obtained with similar to 10 mu M dopamine. Mediation of both effects by dopaminergic D2 recepto rs was supported by several observations: active dopamine doses in mic romolar ranges, quinpirole agonism and eticlopride antagonism, D2-char acteristic rank order of potency among the three agonists tested, and specific binding of a selective D2-like radioligand to 13.S.1.24 cells . The present data altogether indicated that dopamine commits immortal ized olfactory neuronal cells in vitro either to apoptosis or to olfac tory-like differentiation via D2 dopaminergic receptors.