MRNAs encoding muscarinic and substance p receptors in cultured sympathetic neurons are differentially regulated by LIF or CNTF

Leukemia inhibitory factor (LIF) and ciliary neurotrophic factor (CNTF) have previously been shown to regulate neuronal choice of neurotransmitter. In this present study, these factors were shown to specifically and differentially regulate levels of both muscarinic (subtypes m1, m2, m3, m4, and m5) and substance P receptor (SPR) mRNAs in sympathetic neurons of the rat superior cervical ganglion (SCG) using solution hybridization/RNase protection analysis. In vivo, neonatal rat SCG expressed predominantly m2 (10.31 ± 0.43 pg mRNA/μg total RNA) and some m1 (1.54 ± 0.84 pg/μg) muscarinic receptor mRNA, which increased developmentally to adult levels (m2 mRNA levels being 60% higher than those in neonates). By contrast, m3, m4, and m5 subtype mRNAs were much less abundant at all time points measured. A similar developmental regulation was found in dissociated SCG neurons in vitro. After 16 days in culture, m2 mRNA increased 334% to 15.76 ±0.68 pg/μg, while m1 mRNA changed little (2.03±1.00 pg/μg). However, LIF or CNTF treatment (5 ng/ml, 14 days) in sister cultures completely blocked this developmental increase. Further, LIF treatment blocked the normal muscarinic receptor-mediated increase in intracellular calcium (fura-2 imaging), indicating a functional change in receptor phenotype. By contrast, levels of SPR mRNA, which were low in untreated cultures (0.037 ± 0.025 pg SPR mRNA/μg total RNA), were elevated by LIF or CNTF treatment, to 0.866 ± 0.034 pg/μg and 0.662 ± 0.148 pg/μg, respectively. These observations indicate that muscarinic and SPR receptor expression are differentially regulated by the same factors in SCG neurons and that neuronal choice of receptor phenotype may be, at least in part, specifically regulated by cytokines/growth factors in the cellular milieu.