Differential expression and regulation of the high-affinity choline transporter CHT1 and choline acetyltransferase in neurons of superior cervical ganglia

Previous studies revealed that leukemia inhibitory factor (LIF) and retinoic acid (RA) induce a noradrenergic to cholinergic switch in cultured sympathetic neurons of superior cervical ganglia (SCG) by up-regulating the coordinate expression of choline acetyltransferase (ChAT) and the vesicular acetylcholine transporter. Here, we examined the effect of both factors on high-affinity choline uptake (HACU) and on expression of the high-affinity choline transporter CHT1. We found that HACU and CHT1-mRNA levels are up-regulated by LIF and down-regulated by RA in these neurons. Thus, in contrast to LIF, RA differentially regulates the expression of the presynaptic cholinergic proteins. Moreover, we showed that untreated SCG neurons express HACU and CHT1-mRNAs at much higher levels than ChAT activity and transcripts. In intact SCG, CHT1-mRNAs are abundant and synthesized by the noradrenergic neurons themselves. This study provides the first example of CHT1 expression in neurons which do not use acetylcholine as neurotransmitter.