[Reversal of neuronal polarity in vitro]

The mechanisms for neuronal polarity are not well understood. We recently developed two experimental systems in which neuronal polarity is altered in vitro. (1) Cerebral cortical neurons of E18 rats were plated on a sheet of astroglial cells. A time-lapse analysis revealed that GABAergic neurons are highly motile. Migrating neurons often reversed their direction. The reversal of migration was accompanied with a disappearance of the growth cone at the leading process and an appearance of it at the trailing process. A translocation of the Golgi apparatus was often observed when migration was reversed. (2) To observe the reversal of neuronal polarity in vitro, we isolated neurons from the neonatal rat cerebral cortex. Neurons that exhibited an apical dendrite with a length of > 100 micro m were monitored for 3 days in culture. In 66% of the neurons examined, a new axon appeared to form from the tip of the original dendrite. The distal half of the original dendrite was converted into axons. Time-lapse video microscopy demonstrated that the axon regeneration from dendritic tips required a significantly longer time than axon regeneration from minor processes did. We hope these two experimental systems will be useful in investigating the mechanisms for neuronal polarity