Is there an endogenous bungarotoxin-like molecule in the vertebrate central nervous system?

It has been postulated that there is an endogenous bungarotoxin-like ligand in rat brain which can inhibit the binding of α-bungarotoxin (α-BGT) to its target nicotinic acetylcholine (ACh) receptor. We have examined this further by testing the ability of rat and chick brain and spinal cord extracts to inhibit the binding of α-BGT to ACh receptors in cultured chick and rat myotubes. We find no evidence for inhibition by any of these extracts, and thus cannot support the hypothesis of an endogenous α-BGT-like ligand.