Differential regulation of muscarinic and nicotinic cholinergic receptors and their mRNAs in cultured sympathetic neurons.

Mechanisms regulating expression of neuronal muscarinic and nicotinic receptors were examined in cultures of neonatal rat sympathetic neurons. Two factors known to stimulate cholinergic transmitter development in sympathetic neurons were examined for their effects on cholinergic receptor expression. A membrane associated factor (MANS46) and a diffusible factor produced by cultured rat fibroblasts (RFCM) each decreased muscarinic receptor number. By contrast, neither treatment altered levels of nicotinic receptors. Levels of muscarinic (m2) receptor mRNA were decreased by MANS but not by RFCM, indicating that effects of the two treatments were mediated by different mechanisms. Neither MANS nor RFCM altered levels of nicotinic alpha 3 or beta 2 mRNAs, consistent with the lack of change in numbers of nicotinic receptors. These observations indicate that receptor phenotype in developing neurons is subject to regulation by multiple epigenetic factors. Further, the same signals which regulate transmitter development may also regulate receptor expression in sympathetic neurons.