Specific down-regulation of the alpha-bungarotoxin binding component on chick autonomic neurons by ciliary neuronotrophic factor

Abstract

Chick ciliary ganglion neurons have a cholinergic membrane component that binds alpha-bungarotoxin with high affinity but has no known function. The component is different from the nicotinic ACh receptor on the neurons that mediates cholinergic transmission through the ganglion. Ciliary neuronotrophic factor (CNTF) has been shown to enhance the survival of ciliary ganglion neurons in cell culture and has been postulated to act as a target-derived trophic factor for the neurons in vivo. We show here that a factor indistinguishable from CNTF specifically down-regulates alpha-bungarotoxin binding sites on the neurons while increasing cell growth and the number of ACh receptors on the cells. Similar effects, though reduced in magnitude, are seen with chick sympathetic neurons. CNTF has no effect on the number of ACh receptors found on chick myotubes in culture. The down-regulation of alpha-bungarotoxin binding sites on neurons caused by CNTF occurs with a half-time of about 19 hr and is largely reversed within a 4 d period following CNTF removal. It is distinct from the down-regulation caused by cholinergic agonists. Nerve growth factor and fibroblast growth factor have no apparent effect on the number of alpha-bungarotoxin binding sites on the neurons, though fibroblast growth factor does stimulate neuronal growth. The results indicate that the effects of CNTF on the alpha-bungarotoxin binding component are both novel for a growth factor and specific, and they suggest a relationship between the component and the regulation of growth by the target tissue.

Reciprocal Regulation of Ciliary Neurotrophic Factor Receptors and Acetylcholine Receptors during Synaptogenesis in Embryonic Chick Atria

“…Nonspecific binding was determined in the presence of 10 M atropine. Nicotinic acetylcholine receptors were quantified on intact ciliary ganglion neurons using 125 I-␣-bungarotoxin as described previously (Halvorsen and Berg, 1989).…”

“…These effects are much more specific for C N TF on ciliary ganglion neurons than is assessing cell survival (Halvorsen and Berg, 1989;Eckenstein et al, 1990). Treatment of ciliary ganglion neurons with heart extracts produced an increase in cell growth and a downregulation of 125 I-␣-bungarotoxin binding (Fig.…”

“…CNTF also has survival activity for motor, sensory, sympathetic, and hippocampal neurons, regulates nicotinic acetylcholine receptors on autonomic neurons, and regulates neurotransmitter expression in sympathetic and central neurons (Halvorsen and Berg, 1989;Oppenheim et al, 1991;Ip and Yancopoulos, 1994;Lewis et al, 1994;Sendtner et al, 1994;Sun et al, 1994). CNTF and LIF may have important effects on skeletal neuromuscular junction development, maintenance, and regeneration (English and Schwartz, 1995;Ip et al, 1995;Li et al, 1995;Stoop and Poo, 1995;Jordan, 1996;Pennica et al, 1996;Kurek et al, 1997).…”

“…used as a source of putative C N TF-containing 20 -25 kDa material and were tested on cultured ciliary ganglion neurons for stimulation of cell growth and regulation of ␣-bungarotoxinbinding nicotinic acetylcholine receptors (Halvorsen and Berg, 1989;Koshlukova et al, 1996). These effects are much more specific for C N TF on ciliary ganglion neurons than is assessing cell survival (Halvorsen and Berg, 1989;Eckenstein et al, 1990).…”

Regulatory mechanisms that govern nicotinic synapse formation in neurons

“…Ciliary neurotrophic factor (CNTF), a trophic factor expressed in the muscles innervated by CG neurons, specifically downregules ␣7-nAChR protein levels, but upregulates ␣3-nAChR protein levels (Halvorsen and Berg, 1989;Finn and Nishi, 1996). A soluble 50-kDa fraction isolated from embryonic eye tissue increases both ␣3-nAChR and ␣7-nAChR protein levels, and ACh-induced currents in cultured CG neurons (Halvorsen et al, 1991).…”