Retinoic acid regulates the morphological development of sympathetic neurons

Interactions between all-trans-retinoic acid (RA) and bone morphogenetic pr oteins (BMPs) affect the expression of neurotrophin receptors in sympatheti c neurons (Kobayashi et al., 1998), In this study, we examined the possibil ity that similar interactions might regulate the morphological development of these neurons. Under control conditions, embryonic rat sympathetic neuro ns formed axons but not dendrites; cells exposed to RA had a similar appear ance. Profuse dendritic growth was observed upon exposure to BMP-7, and thi s was reduced by similar to 70% by RA. This inhibitory effect of RA was med iated primarily by retinoic acid receptors (RARs) and it exhibited substant ial specificity because it was not associated with changes in either axonal elongation or cell survival. Moreover, mRNAs for enzymes required for synt hesis of RA were expressed in the sympathetic neurons and retinoid activity was released from superior cervical ganglia, These observations suggest th at retinoids may function as endogenous morphogens and regulate neural cell shape and polarity in developing sympathetic ganglia, (C) 2000 John Wiley & Sons, Inc.