alpha-Bungarotoxin blocks nicotinic transmission in the avian ciliary ganglion

Abstract

alpha-Bungarotoxin binds to nicotinic receptors in skeletal muscle, blocking neuromuscular transmission. Because this toxin has recently been shown to bind to chicken ciliary ganglia, an attempt has been made to determine whether it also blocks nicotinic transmission in this ganglion, alpha-Bungarotoxin (1 micrometer) completely blocked nicotinic transmission in both the ciliary and choroid neurons of chicken and pigeon ciliary ganglia. The effect of the toxin could be partially reversed by prolonged washing (2--8 hr). Incubation of ganglia with d-tubocurarine (0.1 mM) prior to the addition of alpha-bungarotoxin significantly decreased the duration of the washout period necessary to restore transmission. These results suggest that d-tubocurarine and alpha-bungarotoxin are interacting with the same receptor. Under similar conditions, alpha-bungarotoxin did not block nicotinic transmission in the rat superior cervical ganglion, in agreement with previous reports. The avian ciliary ganglion is the only vertebrate autonomic ganglion in which both alpha-bungarotoxin binding and alpha-bungarotoxin blockade of transmission have been shown to occur. This ganglion therefore provides a model system for using alpha-bungarotoxin to study neuronal nicotinic receptors.