Regulation of neuronal differentiation by retinoic acid alone and in cooperation with thyroid hormone or hydrocortisone.

Cultures highly enriched in neurons obtained from embryonic mouse cerebra were used to demonstrate that: (1) at the optimum concentration of 10(-8) M retinoic acid stimulated the neurons to produce axon- and dendrite-like structures as determined by phase contrast and fluorescent microscopy; (2) the same concentration of retinoic acid stimulated acetyl cholinesterase and choline acetyltransferase activities; (3) treatment of neurons of either prenatal or neonatal equivalent age with retinoic acid produced a sustained stimulation of neuronal differentiation, and (4) retinoic acid cooperatively stimulated neuronal differentiation with either thyroid hormone or hydrocortisone.