Leukemia Inhibitory Factor and Ciliary Neurotrophic Factor Regulate Expression of Muscarinic Receptors in Cultured Sympathetic Neurons

Abstract

Regulation of muscarinic receptor expression was studied in cultured sympathetic neurons of the neonatal rat superior cervical ganglion (SCG). Leukemia inhibitory factor (LIF) and ciliary neurotrophic factor (CNTF), both previously shown to regulate neurotransmitter development in cultured SCG neurons (Yamamori et al., 1989; Saadat et al., 1989), were examined for effects on receptor expression. Exposure of SCG neurons to LIF or CNTF (5 ng/ml) prevented the normal developmental increase in muscarinic receptors as measured by whole cell binding of N -methyl[ 3H]scopolamine. Reduction in receptor binding was detected within 2 to 4 days of treatment, with a 65-80% reduction after 16 days. Scatchard analysis demonstrated a reduction in total receptor number ( B max) with no significant change in receptor affinity ( K d). Concentrations of 1 ng/ml of either factor reduced receptor expression with near-maximal effectiveness at doses of 10 ng/ml. The decrease in muscarinic receptors was not blocked by atropine, indicating that it was not agonist induced. Treatment with LIF or CNTF did not affect the survival of cultured neurons. Further, effects on receptor expression were reversible after discontinuance of treatment. Finally, treatment with either factor increased overall protein synthesis, indicating the integrity of cellular metabolism of cultures and hence the specificity of the decrease in muscarinic receptor number. LIF and CNTF thus regulate receptor as well as neurotransmitter development and could therefore play a role during synaptogenesis in the developing nervous system.