AGE-DEPENDENT NEUROTRANSMITTER PLASTICITY OF CILIARY GANGLION NEURONS

We have examined neurotransmitter plasticity in postmitotic cholinergi c neurons isolated from 6.5- to 11-day-old embryonic quail ciliary gan glia. Purified neurons were labeled with Dil, transplanted into the tr unk of young chick embryos, and assayed for catecholamine content and [H-3]thymidine uptake 4 to 5 days later. For ciliary neurons derived f rom 6.5- to 8-day-old embryos, as many as 25% (average of 9% overall) expressed catecholamines in the host sympathetic ganglia, migratory st ream, aortic plexuses, and adrenal medulla. In contrast, neurons from >8-day-old ganglia did not acquire or produce detectable catecholamine s, indicating a limited time period over which phenotypic conversion c an occur in vivo. As a control, ciliary neurons were also injected int o the head mesenchyme of young embryos; no catecholamine expression wa s observed. Interestingly, after transplantation some Dil-labeled post mitotic ciliary neurons took up [H-3]thymidine with or without phenoty pic change. These results suggest that phenotypic plasticity in ciliar y neurons is age-dependent, is location-dependent, and may involve res umption of DNA replication, a characteristic feature of some different iating adrenergic sympathetic neurons. Apoptosis of a few proliferatin g transplanted cells may be induced independently or in association wi th transmitter change.