Kappa-bungarotoxin blocks nicotinic transmission at an identified invertebrate central synapse

A comparison was made between the effects of kappa-bungarotoxin and alpha-bungarotoxin upon nicotinic cholinergic transmission at an identified synapse (the cereal afferent, giant interneurone 2 synapse) in the central nervous system of the cockroach (Periplaneta americana). kappa-Bungarotoxin, a snake venom kappa-neurotoxin, completely blocked nicotinic unitary excitatory postsynaptic potentials (EPSPs) and evoked composite EPSPs when applied at a concentration of 1.0 x 10(-7) moll-1. No recovery was observed after a 2h wash in normal saline. kappa-Bungarotoxin produced a decrease in acetylcholine-induced nicotinic responses which paralleled decreases in nicotinic synaptic potentials and currents, indicating that kappa-bungarotoxin blocked postsynaptic nicotinic receptors. This blockade appeared to be specific as resting membrane potential, input resistance and the ability to elicit an action potential in response to direct stimulation of giant interneurone 2 were unchanged following prolonged toxin exposures. Samples of alpha-bungarotoxin which were free from kappa-neurotoxin contamination were also found to be potent antagonists of cockroach neuronal nicotinic receptors. It is concluded that the cockroach receptor is the first reported example of a neuronal nicotinic receptor which is sensitive to blockade by both kappa-neurotoxins and alpha-neurotoxins.