CNTF INDUCES RAPHE NEURONAL PRECURSORS TO SWITCH FROM A SEROTONERGIC TO A CHOLINERGIC PHENOTYPE IN-VITRO

Ciliary neurotrophic factor (CNTF) is a multifunctional cytokine that mediates survival and differentiation of neurons as well as many other cell types. In this study, CNTF and leukemia inhibitory factor (LIF) reduced the apparent number of primary serotonergic neurons in E14 rap he culture by 90% as determined by immunocytochemistry for serotonin ( 5HT). The reduction in 5HT cell number was not due to neuronal loss as removal of CNTF after 4 days in culture resulted in a partial restitu tion of the serotonergic phenotype. In the RN46A serotonergic cell lin e which is induced to become serotonergic by brain-derived neurotrophi c factor (BDNF), the addition of CNTF suppressed tryptophan hydroxylas e and 5HT synthesis and increased choline acetyl transferase (ChAT) ex pression by 6-fold and ChAT activity by 20- to 30-fold over 12 days. A s with the primary neurons, removal and replacement of CNTF with BDNF after 4 days resulted in a partial restitution of 5HT expression. More over, other members of the CNTF-cytokine family that use gp130 and/or LIF receptor beta as their signal transducing receptors-LIF, oncostati n M, interleukin 6, and interleukin 11-had similar effects on increasi ng ChAT activity and reducing 5HT expression in RN46A cells. Analysis of 5HT levels showed no significant difference in the amount of seroto nin between wild-type and CNTFR alpha knockout mice at birth, suggesti ng that the potential to switch phenotype mediated through CNTFR alpha is a latent property of neuroepithelial precursors in the raphe nucle us.